Apache HttpClient - Quick Guide

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Apache HttpClient - Overview

The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. This is the foundation for data communication for the World Wide Web (i.e., Internet) since 1990. HTTP is a generic and stateless protocol which can be used for other purposes as well using extensions of its request methods, error codes, and headers.

Basically, HTTP is a TCP/IP based communication protocol, that is used to deliver data (HTML files, image files, query results, etc.) on the World Wide Web. The default port is TCP 80, but other ports can be used as well. It provides a standardized way for computers to communicate with each other. HTTP specification defines how clients' request data will be constructed and sent to the server, and how the servers respond to these requests.

What is Http Client

Http client is a transfer library, it resides on the client side, sends and receives HTTP messages. It provides up to date, feature-rich and, efficient implementation which meets the recent HTTP standards.

In addition to this using client library, one can build HTTP based applications such as web browsers, web service clients, etc.

Features of Http Client

Following are the prominent features of Http client −

  • HttpClient library implements all the available HTTP methods.

  • HttpClient library provides APIs to secure the requests using the Secure Socket Layer protocol.

  • Using HttpClient, you can establish connections using proxies.

  • You can authenticate connections using authentication schemes such as Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session etc.

  • HttpClient library supports sending requests through multiple threads. It manages multiple connections established from various threads using ClientConnectionPoolManager.

  • Using Apache HttpClient library, you can set connection timeouts.

Apache HttpClient - Environment Setup

In this chapter, we will explain how to set an environment for HttpClient in Eclipse IDE. Before proceeding with the installation, make sure that you already have Eclipse installed in your system. If not, download and install Eclipse.

For more information on Eclipse, please refer to our Eclipse Tutorial.

Step 1 - Download the dependency JAR file

Open the official homepage of the HttpClient (components) website and go to the download page

HttpComponents Downloads

Then, download the latest stable version of HttpClient. Here, throughout the tutorial, we are using the version 4.5.6 hence download the file 4.5.6.zip.

Within the downloaded folder, you will find a folder named lib and this contains the required Jar files that are to be added in the classpath of your project, to work with HttpClient.

Step 2 - Create a project and set build path

Open eclipse and create a sample project. Right click on the project select the option Build Path → Configure Build Path as shown below.

Build Path

In the Java Build Path frame in the Libraries tab, click on Add External JARs.

Add External Jars

And select all the jar files in the lib folder and, click on Apply and Close.

Jar Files

You are all set to work with HttpClient library in eclipse.

Apache HttpClient - Http Get Request

The GET method is used to retrieve information from the given server using a given URI. Requests using GET should only retrieve data and should have no other effect on the data.

The HttpClient API provides a class named HttpGet which represents the get request method.

Follow the steps given below to send a get request using HttpClient library

Step 1 - Create a HttpClient object

The createDefault() method of the HttpClients class returns a CloseableHttpClient object, which is the base implementation of the HttpClient interface.

Using this method, create an HttpClient object as shown below −

CloseableHttpClient httpclient = HttpClients.createDefault();

Step 2 - Create an HttpGet Object

The HttpGet class represents the HTTPGET request which retrieves the information of the given server using a URI.

Create a HTTP GET request by instantiating this class. The constructor of this class accepts a String value representing the URI.

HttpGet httpget = new HttpGet("http://www.howcodex.com/");

Step 3 - Execute the Get Request

The execute() method of the CloseableHttpClient class accepts a HttpUriRequest (interface) object (i.e. HttpGet, HttpPost, HttpPut, HttpHead etc.) and returns a response object.

Execute the request using this method as shown below −

HttpResponse httpresponse = httpclient.execute(httpget);

Example

Following is an example which demonstrates the execution of the HTTP GET request using HttpClient library.

import java.util.Scanner;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class HttpGetExample {
 
   public static void main(String args[]) throws Exception{
 
      //Creating a HttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();

      //Creating a HttpGet object
      HttpGet httpget = new HttpGet("https://www.howcodex.com/ ");

      //Printing the method used
      System.out.println("Request Type: "+httpget.getMethod());

      //Executing the Get request
      HttpResponse httpresponse = httpclient.execute(httpget);

      Scanner sc = new Scanner(httpresponse.getEntity().getContent());

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());
      while(sc.hasNext()) {
         System.out.println(sc.nextLine());
      }
   }
}

Output

The above program generates the following output −

Request Type: GET
<!DOCTYPE html>
<!--[if IE 8]><html class = "ie ie8"> <![endif]-->
<!--[if IE 9]><html class = "ie ie9"> <![endif]-->
<!--[if gt IE 9]><!-->
<html lang = "en-US"> <!--<![endif]-->
<head>
<!-- Basic -->
<meta charset = "utf-8">
<title>Parallax Scrolling, Java Cryptography, YAML, Python Data Science, Java
i18n, GitLab, TestRail, VersionOne, DBUtils, Common CLI, Seaborn, Ansible,
LOLCODE, Current Affairs 2018, Apache Commons Collections</title>
<meta name = "Description" content = "Parallax Scrolling, Java Cryptography, YAML,
Python Data Science, Java i18n, GitLab, TestRail, VersionOne, DBUtils, Common
CLI, Seaborn, Ansible, LOLCODE, Current Affairs 2018, Intellij Idea, Apache
Commons Collections, Java 9, GSON, TestLink, Inter Process Communication (IPC),
Logo, PySpark, Google Tag Manager, Free IFSC Code, SAP Workflow"/>
<meta name = "Keywords" content = "Python Data Science, Java i18n, GitLab,
TestRail, VersionOne, DBUtils, Common CLI, Seaborn, Ansible, LOLCODE, Gson,
TestLink, Inter Process Communication (IPC), Logo"/>
<meta http-equiv = "X-UA-Compatible" content = "IE = edge">
<meta name = "viewport" content = "width = device-width,initial-scale = 1.0,userscalable = yes">
<link href = "https://cdn.muicss.com/mui-0.9.39/extra/mui-rem.min.css"
rel = "stylesheet" type = "text/css" />
<link rel = "stylesheet" href="/questions/css/home.css?v = 3" />
<script src = "/questions/js/jquery.min.js"></script>
<script src = "/questions/js/fontawesome.js"></script>
<script src = "https://cdn.muicss.com/mui-0.9.39/js/mui.min.js"></script>
</head>
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
</script>
</body>
</html>

Apache HttpClient - Http Post Request

A POST request is used to send data to the server; for example, customer information, file upload, etc., using HTML forms.

The HttpClient API provides a class named HttpPost which represents the POST request.

Follow the steps given below to send a HTTP POST request using HttpClient library.

Step 1 - Create an HttpClient Object

The createDefault() method of the HttpClients class returns an object of the class CloseableHttpClient, which is the base implementation of the HttpClient interface.

Using this method, create an HttpClient object.

CloseableHttpClient httpClient = HttpClients.createDefault();

Step 2 - Create HttpPost Object

The HttpPost class represents the HTTP POST request. This sends required data and retrieves the information of the given server using a URI.

Create this request by instantiating the HttpPost class and pass a string value representing the URI, as a parameter to its constructor.

HttpGet httpGet = new HttpGet("http://www.howcodex.com/");

Step 3 - Execute the Get Request

The execute() method of the CloseableHttpClient object accepts a HttpUriRequest (interface) object (i.e. HttpGet, HttpPost, HttpPut, HttpHead etc.) and returns a response object.

HttpResponse httpResponse = httpclient.execute(httpget);

Example

Following is an example which demonstrates the execution of the HTTP POST request using HttpClient library.

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class HttpPostExample {
 
   public static void main(String args[]) throws Exception{
 
      //Creating a HttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();

      //Creating a HttpGet object
      HttpPost httppost = new HttpPost("https://www.howcodex.com/");

      //Printing the method used
      System.out.println("Request Type: "+httppost.getMethod());

      //Executing the Get request
      HttpResponse httpresponse = httpclient.execute(httppost);

      Scanner sc = new Scanner(httpresponse.getEntity().getContent());

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());
      while(sc.hasNext()) {
         System.out.println(sc.nextLine());
      }
   }
}

Output

The above program generates the following output.

Request Type: POST
<!DOCTYPE html>
<!--[if IE 8]><html class = "ie ie8"> <![endif]-->
<!--[if IE 9]><html class = "ie ie9"> <![endif]-->
<!--[if gt IE 9]><!--> 
<html lang = "en-US"> <!--<![endif]-->
<head>
<!-- Basic -->
<meta charset = "utf-8">
<title>Parallax Scrolling, Java Cryptography, YAML, Python Data Science, Java
i18n, GitLab, TestRail, VersionOne, DBUtils, Common CLI, Seaborn, Ansible,
LOLCODE, Current Affairs 2018, Apache Commons Collections</title>
<meta name = "Description" content = "Parallax Scrolling, Java Cryptography, YAML,
Python Data Science, Java i18n, GitLab, TestRail, VersionOne, DBUtils, Common
CLI, Seaborn, Ansible, LOLCODE, Current Affairs 2018, Intellij Idea, Apache
Commons Collections, Java 9, GSON, TestLink, Inter Process Communication (IPC),
Logo, PySpark, Google Tag Manager, Free IFSC Code, SAP Workflow"/>
<meta name = "Keywords" content="Python Data Science, Java i18n, GitLab,
TestRail, VersionOne, DBUtils, Common CLI, Seaborn, Ansible, LOLCODE, Gson,
TestLink, Inter Process Communication (IPC), Logo"/>
<meta http-equiv = "X-UA-Compatible" content = "IE = edge">
<meta name = "viewport" conten t= "width = device-width,initial-scale = 1.0,userscalable = yes">
<link href = "https://cdn.muicss.com/mui-0.9.39/extra/mui-rem.min.css"
rel = "stylesheet" type = "text/css" />
<link rel = "stylesheet" href = "/questions/css/home.css?v = 3" />
<script src = "/questions/js/jquery.min.js"></script>
<script src = "/questions/js/fontawesome.js"></script>
<script src = "https://cdn.muicss.com/mui-0.9.39/js/mui.min.js"></script>
</head>
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
</script>
</body>
</html>

Apache HttpClient - Response Handlers

Processing the HTTP responses using the response handlers is recommended. In this chapter, we are going to discuss how to create response handlers and how to use them to process a response.

If you use the response handler, all the HTTP connections will be released automatically.

Creating a response handler

The HttpClient API provides an interface known as ResponseHandler in the package org.apache.http.client. In order to create a response handler, implement this interface and override its handleResponse() method.

Every response has a status code and if the status code is in between 200 and 300, that means the action was successfully received, understood, and accepted. Therefore, in our example, we will handle the entities of the responses with such status codes.

Executing the request using response handler

Follow the steps given below to execute the request using a response handler.

Step 1 - Create an HttpClient Object

The createDefault() method of the HttpClients class returns an object of the class CloseableHttpClient, which is the base implementation of the HttpClient interface. Using this method create an HttpClient object

CloseableHttpClient httpclient = HttpClients.createDefault();

Step 2 - Instantiate the Response Handler

Instantiate the response handler object created above using the following line of code −

ResponseHandler<String> responseHandler = new MyResponseHandler();

Step 3 - Create a HttpGet Object

The HttpGet class represents the HTTP GET request which retrieves the information of the given server using a URI.

Create an HttpGet request by instantiating the HttpGet class and by passing a string representing the URI as a parameter to its constructor.

ResponseHandler<String> responseHandler = new MyResponseHandler();

Step 4 - Execute the Get request using response handler

The CloseableHttpClient class has a variant of execute() method which accepts two objects ResponseHandler and HttpUriRequest, and returns a response object.

String httpResponse = httpclient.execute(httpget, responseHandler);

Example

Following example demonstrates the usage of response handlers.

import java.io.IOException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

class MyResponseHandler implements ResponseHandler<String>{
 
   public String handleResponse(final HttpResponse response) throws IOException{

      //Get the status of the response
      int status = response.getStatusLine().getStatusCode();
      if (status >= 200 && status < 300) {
         HttpEntity entity = response.getEntity();
         if(entity == null) {
            return "";
         } else {
            return EntityUtils.toString(entity);
         }

      } else {
         return ""+status;
      }
   }
}

public class ResponseHandlerExample {
   
   public static void main(String args[]) throws Exception{
 
      //Create an HttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();

      //instantiate the response handler
      ResponseHandler<String> responseHandler = new MyResponseHandler();

      //Create an HttpGet object
      HttpGet httpget = new HttpGet("http://www.howcodex.com/");

      //Execute the Get request by passing the response handler object and HttpGet object
      String httpresponse = httpclient.execute(httpget, responseHandler);

      System.out.println(httpresponse);
   }
}

Output

The above programs generate the following output −

<!DOCTYPE html>
<!--[if IE 8]><html class = "ie ie8"> <![endif]-->
<!--[if IE 9]><html class = "ie ie9"> <![endif]-->
<!--[if gt IE 9]><!-->
<html lang = "en-US"> <!--<![endif]-->
<head>
<!-- Basic -->
<meta charset = "utf-8">
<meta http-equiv = "X-UA-Compatible" content = "IE = edge">
<meta name = "viewport" content = "width = device-width,initial-scale = 1.0,userscalable = yes">
<link href = "https://cdn.muicss.com/mui-0.9.39/extra/mui-rem.min.css"
rel = "stylesheet" type = "text/css" />
<link rel = "stylesheet" href = "/questions/css/home.css?v = 3" />
<script src = "/questions/js/jquery.min.js"></script>
<script src = "/questions/js/fontawesome.js"></script>
<script src = "https://cdn.muicss.com/mui-0.9.39/js/mui.min.js"></script>
</head>
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
<script>
window.dataLayer = window.dataLayer || [];
function gtag() {dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'UA-232293-17');
</script>
</body>

Apache HttpClient - Closing Connection

If you are processing HTTP responses manually instead of using a response handler, you need to close all the http connections by yourself. This chapter explains how to close the connections manually.

While closing HTTP connections manually follow the steps given below −

Step 1 - Create an HttpClient object

The createDefault() method of the HttpClients class returns an object of the class CloseableHttpClient, which is the base implementation of the HttpClient interface.

Using this method, create an HttpClient object as shown below −

CloseableHttpClient httpClient = HttpClients.createDefault();

Step 2 - Start a try-finally block

Start a try-finally block, write the remaining code in the programs in the try block and close the CloseableHttpClient object in the finally block.

CloseableHttpClient httpClient = HttpClients.createDefault();
try{
   //Remaining code . . . . . . . . . . . . . . .
}finally{
   httpClient.close();
}

Step 3 - Create a HttpGetobject

The HttpGet class represents the HTTP GET request which retrieves the information of the given server using a URI.

Create a HTTP GET request by instantiating the HttpGet class by passing a string representing the URI.

HttpGet httpGet = new HttpGet("http://www.howcodex.com/");

Step 4 - Execute the Get request

The execute() method of the CloseableHttpClient object accepts a HttpUriRequest (interface) object (i.e. HttpGet, HttpPost, HttpPut, HttpHead etc.) and returns a response object.

Execute the request using the given method −

HttpResponse httpResponse = httpclient.execute(httpGet);

Step 5 - Start another (nested) try-finally

Start another try-finally block (nested within the previous try-finally), write the remaining code in the programs in this try block and close the HttpResponse object in the finally block.

CloseableHttpClient httpclient = HttpClients.createDefault();
try{
   . . . . . . .
   . . . . . . .
   CloseableHttpResponse httpresponse = httpclient.execute(httpget);
   try{
      . . . . . . .
      . . . . . . .
   }finally{
      httpresponse.close();
   }
}finally{
   httpclient.close();
}

Example

Whenever you create/obtain objects such as request, response stream, etc., start a try finally block in the next line, write the remaining code within the try and close the respective object in the finally block as demonstrated in the following program −

import java.util.Scanner;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class CloseConnectionExample {
   
   public static void main(String args[])throws Exception{
 
      //Create an HttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();

      try{
         //Create an HttpGet object
         HttpGet httpget = new HttpGet("http://www.howcodex.com/");

         //Execute the Get request
         CloseableHttpResponse httpresponse = httpclient.execute(httpget);

         try{
            Scanner sc = new Scanner(httpresponse.getEntity().getContent());
            while(sc.hasNext()) {
               System.out.println(sc.nextLine());
            }
         }finally{
            httpresponse.close();
         }
      }finally{
         httpclient.close();
      }
   }
}

Output

On executing the above program, the following output is generated −

<!DOCTYPE html>
<!--[if IE 8]><html class = "ie ie8"> <![endif]-->
<!--[if IE 9]><html class = "ie ie9"> <![endif]-->
<!--[if gt IE 9]><!-->
<html lang = "en-US"> <!--<![endif]-->
<head>
<!-- Basic -->
<meta charset = "utf-8">
<meta http-equiv = "X-UA-Compatible" content = "IE = edge">
<meta name = "viewport" content = "width = device-width,initial-scale = 1.0,userscalable = yes">
<link href = "https://cdn.muicss.com/mui-0.9.39/extra/mui-rem.min.css"
rel = "stylesheet" type = "text/css" />
<link rel = "stylesheet" href = "/questions/css/home.css?v = 3" />
<script src = "/questions/js/jquery.min.js"></script>
<script src = "/questions/js/fontawesome.js"></script>
<script src = "https://cdn.muicss.com/mui-0.9.39/js/mui.min.js"></script>
</head>
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 
<script>
window.dataLayer = window.dataLayer || [];
function gtag() {dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'UA-232293-17');
</script>
</body>
</html>

Apache HttpClient - Aborting a Request

You can abort the current HTTP request using the abort() method, i.e., after invoking this method, on a particular request, execution of it will be aborted.

If this method is invoked after one execution, responses of that execution will not be affected and the subsequent executions will be aborted.

Example

If you observe the following example, we have created a HttpGet request, printed the request format used using the getMethod().

Then, we have carried out another execution with the same request. Printed the status line using the 1st execution again. Finally, printed the status line of the second execution.

As discussed, the responses of the 1st execution (execution before abort method) are printed (including the second status line that is written after the abort method) and, all the subsequent executions of the current request after the abort method are failed invoking an exception.

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class HttpGetExample {
   public static void main(String args[]) throws Exception{
   
      //Creating an HttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();

      //Creating an HttpGet object
      HttpGet httpget = new HttpGet("http://www.howcodex.com/");

      //Printing the method used
      System.out.println(httpget.getMethod());
 
      //Executing the Get request
      HttpResponse httpresponse = httpclient.execute(httpget);

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());

      httpget.abort();
      System.out.println(httpresponse.getEntity().getContentLength());
 
      //Executing the Get request
      HttpResponse httpresponse2 = httpclient.execute(httpget);
      System.out.println(httpresponse2.getStatusLine());
   }
}

Output

On executing, the above program generates the following output −

On executing, the above program generates the following output.
GET
HTTP/1.1 200 OK
-1
Exception in thread "main" org.apache.http.impl.execchain.RequestAbortedException:
Request aborted
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:180)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)
at HttpGetExample.main(HttpGetExample.java:32)

Apache HttpClient - Interceptors

Interceptors are those which helps to obstruct or change requests or responses. Protocol interceptors in general act upon a specific header or a group of related headers. HttpClient library provides support for interceptors.

Request interceptor

The HttpRequestInterceptor interface represents the request interceptors. This interface contains a method known as a process in which you need to write the chunk of code to intercept the requests.

On the client side, this method verifies/processes the requests before sending them to the server and, on the server side, this method is executed before evaluating the body of the request.

Creating request interceptor

You can create a request interceptor by following the steps given below.

Step 1 - Create an object of HttpRequestInterceptor

Create an object of the HttpRequestInterceptor interface by implementing its abstract method process.

HttpRequestInterceptor requestInterceptor = new HttpRequestInterceptor() {


@Override
 public void process(HttpRequest request, HttpContext context) throws
HttpException, IOException {
   //Method implementation . . . . .
};

Step 2 - Instantiate CloseableHttpClient object

Build a custom CloseableHttpClient object by adding above created interceptor to it as shown below −

//Creating a CloseableHttpClient object
CloseableHttpClient httpclient =
HttpClients.custom().addInterceptorFirst(requestInterceptor).build();

Using this object, you can carry out the request executions as usual.

Example

Following example demonstrates the usage of request interceptors. In this example, we have created a HTTP GET request object and added three headers: sample-header, demoheader, and test-header to it.

In the processor() method of the interceptor, we are verifying the headers of the request sent; if any of those headers is sample-header, we are trying to remove it and display the list of headers of that particular request.

import java.io.IOException;
import org.apache.http.Header;
import org.apache.http.HttpException;
import org.apache.http.HttpRequest;
import org.apache.http.HttpRequestInterceptor;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicHeader;
import org.apache.http.protocol.HttpContext;

public class InterceptorsExample {
 
   public static void main(String args[]) throws Exception{
      
      //Creating an HttpRequestInterceptor
      HttpRequestInterceptor requestInterceptor = new HttpRequestInterceptor() {
         @Override
         public void process(HttpRequest request, HttpContext context) throws
         HttpException, IOException {
            if(request.containsHeader("sample-header")) {
               System.out.println("Contains header sample-header, removing it..");
               request.removeHeaders("sample-header"); 
            }
            //Printing remaining list of headers
            Header[] headers= request.getAllHeaders();
            for (int i = 0; i<headers.length;i++) {
               System.out.println(headers[i].getName());
            }
         }
      };

      //Creating a CloseableHttpClient object
      CloseableHttpClient httpclient =
      HttpClients.custom().addInterceptorFirst(requestInterceptor).build();

      //Creating a request object
      HttpGet httpget1 = new HttpGet("https://www.howcodex.com/");

      //Setting the header to it
      httpget1.setHeader(new BasicHeader("sample-header","My first header"));
      httpget1.setHeader(new BasicHeader("demo-header","My second header"));
      httpget1.setHeader(new BasicHeader("test-header","My third header"));

      //Executing the request
      HttpResponse httpresponse = httpclient.execute(httpget1);

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());
   }
}

Output

On executing the above program, the following output is generated −

Contains header sample-header, removing it..
demo-header
test-header
HTTP/1.1 200 OK

Response interceptor

The HttpResponseInterceptor interface represents the response interceptors. This interface contains a method known as process(). In this method, you need to write the chunk of code to intercept the responses.

On the server side, this method verifies/processes the response before sending them to the client, and on the client side, this method is executed before evaluating the body of the response.

Creating response interceptor

You can create a response interceptor by following the steps given below −

Step 1 - Create an object of HttpResponseInterceptor

Create an object of the HttpResponseInterceptor interface by implementing its abstract method process.

HttpResponseInterceptor responseInterceptor = new HttpResponseInterceptor() {
   @Override
   public void process(HttpResponse response, HttpContext context) throws HttpException, IOException {
      //Method implementation . . . . . . . .
   }
};

Step 2: Instantiate CloseableHttpClient object

Build a custom CloseableHttpClient object by adding above created interceptor to it, as shown below −

//Creating a CloseableHttpClient object
CloseableHttpClient httpclient =
HttpClients.custom().addInterceptorFirst(responseInterceptor).build();

Using this object, you can carry out the request executions as usual.

Example

The following example demonstrates the usage of response interceptors. In this example, we have added three headers: sample-header, demo-header, and test-header to the response in the processor.

After executing the request and obtaining the response, we printed names of all the headers of the response using the getAllHeaders() method.

And in the output, you can observe the names of three headers in the list.

import java.io.IOException;
import org.apache.http.Header;
import org.apache.http.HttpException;
import org.apache.http.HttpResponse;
import org.apache.http.HttpResponseInterceptor;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.protocol.HttpContext;

public class ResponseInterceptorsExample {

   public static void main(String args[]) throws Exception{
      
      //Creating an HttpRequestInterceptor
      HttpResponseInterceptor responseInterceptor = new HttpResponseInterceptor() {
         @Override
         public void process(HttpResponse response, HttpContext context) throws
         HttpException, IOException {
            System.out.println("Adding header sample_header, demo-header, test_header to the response");
            response.setHeader("sample-header", "My first header");
            response.setHeader("demo-header", "My second header");
            response.setHeader("test-header", "My third header"); 
         }
      };

      //Creating a CloseableHttpClient object
      CloseableHttpClient httpclient = HttpClients.custom().addInterceptorFirst(responseInterceptor).build();

      //Creating a request object
      HttpGet httpget1 = new HttpGet("https://www.howcodex.com/");

      //Executing the request
      HttpResponse httpresponse = httpclient.execute(httpget1); 

      //Printing remaining list of headers
      Header[] headers = httpresponse.getAllHeaders();
 
      for (int i = 0; i<headers.length;i++) {
         System.out.println(headers[i].getName());
      }
   }
}

Output

On executing, the above program generates the following result −

On executing the above program generates the following output.
Adding header sample_header, demo-header, test_header to the response
Accept-Ranges
Access-Control-Allow-Headers
Access-Control-Allow-Origin
Cache-Control
Content-Type
Date
Expires
Last-Modified
Server
Vary
X-Cache
sample-header
demo-header
test-header

Apache HttpClient - User Authentication

Using HttpClient, you can connect to a website which needed username and password. This chapter explains, how to execute a client request against a site that asks for username and password.

Step 1 - Create a CredentialsProvider object

The CredentialsProvider Interface maintains a collection to hold the user login credentials. You can create its object by instantiating the BasicCredentialsProvider class, the default implementation of this interface.

CredentialsProvider credentialsPovider = new BasicCredentialsProvider();

Step 2 - Set the Credentials

You can set the required credentials to the CredentialsProvider object using the setCredentials() method.

This method accepts two objects as given below −

  • AuthScope object − Authentication scope specifying the details like hostname, port number, and authentication scheme name.

  • Credentials object − Specifying the credentials (username, password).

Set the credentials using the setCredentials() method for both host and proxy as shown below −

credsProvider.setCredentials(new AuthScope("example.com", 80), 
   new UsernamePasswordCredentials("user", "mypass"));
credsProvider.setCredentials(new AuthScope("localhost", 8000), 
   new UsernamePasswordCredentials("abc", "passwd"));

Step 3 - Create a HttpClientBuilder Object

Create a HttpClientBuilder using the custom() method of the HttpClients class.

//Creating the HttpClientBuilder
HttpClientBuilder clientbuilder = HttpClients.custom();

Step 4 - Set the credentialsPovider

You can set the above created credentialsPovider object to a HttpClientBuilder using the setDefaultCredentialsProvider() method.

Set the CredentialProvider object created in the previous step to the client builder by passing it to the CredentialsProvider object() method as shown below.

clientbuilder = clientbuilder.setDefaultCredentialsProvider(credsProvider);

Step 5 - Build the CloseableHttpClient

Build the CloseableHttpClient object using the build() method of the HttpClientBuilder class.

CloseableHttpClient httpclient = clientbuilder.build()

Step 6 - Create a HttpGet object and execute it

Create a HttpRequest object by instantiating the HttpGet class. Execute this request using the execute() method.

//Creating a HttpGet object
HttpGet httpget = new HttpGet("https://www.howcodex.com/ ");

//Executing the Get request
HttpResponse httpresponse = httpclient.execute(httpget);

Example

Following is an example program which demonstrates the execution of a HTTP request against a target site that requires user authentication.

import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.Credentials;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;

public class UserAuthenticationExample {
   
   public static void main(String args[]) throws Exception{
      
      //Create an object of credentialsProvider
      CredentialsProvider credentialsPovider = new BasicCredentialsProvider();

      //Set the credentials
      AuthScope scope = new AuthScope("https://www.howcodex.com/questions/", 80);
      
      Credentials credentials = new UsernamePasswordCredentials("USERNAME", "PASSWORD");
      credentialsPovider.setCredentials(scope,credentials);

      //Creating the HttpClientBuilder
      HttpClientBuilder clientbuilder = HttpClients.custom();

      //Setting the credentials
      clientbuilder = clientbuilder.setDefaultCredentialsProvider(credentialsPovider);

      //Building the CloseableHttpClient object
      CloseableHttpClient httpclient = clientbuilder.build();

      //Creating a HttpGet object
      HttpGet httpget = new HttpGet("https://www.howcodex.com/questions/index.php");

      //Printing the method used
      System.out.println(httpget.getMethod()); 

      //Executing the Get request
      HttpResponse httpresponse = httpclient.execute(httpget);

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());
      int statusCode = httpresponse.getStatusLine().getStatusCode();
      System.out.println(statusCode);

      Header[] headers= httpresponse.getAllHeaders();
      for (int i = 0; i<headers.length;i++) {
         System.out.println(headers[i].getName());
      }
   }
}

Output

On executing, the above program generates the following output.

GET
HTTP/1.1 200 OK
200

Apache HttpClient - Using Proxy

A Proxy server is an intermediary server between the client and the internet. Proxy servers offer the following basic functionalities −

  • Firewall and network data filtering

  • Network connection sharing

  • Data caching

Using HttpClient library, you can send a HTTP request using a proxy. Follow the steps given below −

Step 1 - Create a HttpHost object

Instantiate the HttpHost class of the org.apache.http package by passing a string parameter representing the name of the proxy host, (from which you need the requests to be sent) to its constructor.

//Creating an HttpHost object for proxy
HttpHost proxyHost = new HttpHost("localhost");

In the same way, create another HttpHost object to represent the target host to which requests need to be sent.

//Creating an HttpHost object for target
HttpHost targetHost = new HttpHost("google.com");

Step 2 - Create an HttpRoutePlanner object

The HttpRoutePlanner interface computes a route to a specified host. Create an object of this interface by instantiating the DefaultProxyRoutePlanner class, an implementation of this interface. As a parameter to its constructor, pass the above created proxy host −

//creating a RoutePlanner object
HttpRoutePlanner routePlanner = new DefaultProxyRoutePlanner(proxyhost);

Step 3 - Set the route planner to a client builder

Using the custom() method of the HttpClients class, create a HttpClientBuilder object and, to this object set the route planner created above, using the setRoutePlanner() method.

//Setting the route planner to the HttpClientBuilder object
HttpClientBuilder clientBuilder = HttpClients.custom();

clientBuilder = clientBuilder.setRoutePlanner(routePlanner);

Step 4 - Build the CloseableHttpClient object

Build the CloseableHttpClient object by calling the build() method.

//Building a CloseableHttpClient
CloseableHttpClient httpClient = clientBuilder.build();

Step 5 - Create a HttpGetobject

Create a HTTP GET request by instantiating the HttpGet class.

//Creating an HttpGet object
HttpGet httpGet = new HttpGet("/");

Step 6 - Execute the request

One of the variants of the execute() method accepts an HttpHost and HttpRequest objects and executes the request. Execute the request using this method −

//Executing the Get request
HttpResponse httpResponse = httpclient.execute(targetHost, httpGet);

Example

Following example demonstrates how to send a HTTP request to a server via proxy. In this example, we are sending a HTTP GET request to google.com via localhost. We have printed the headers of the response and the body of the response.

import org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.conn.routing.HttpRoutePlanner;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.DefaultProxyRoutePlanner;
import org.apache.http.util.EntityUtils;

public class RequestViaProxyExample {

   public static void main(String args[]) throws Exception{
 
      //Creating an HttpHost object for proxy
      HttpHost proxyhost = new HttpHost("localhost");

      //Creating an HttpHost object for target
      HttpHost targethost = new HttpHost("google.com");
 
      //creating a RoutePlanner object
      HttpRoutePlanner routePlanner = new DefaultProxyRoutePlanner(proxyhost);

      //Setting the route planner to the HttpClientBuilder object
      HttpClientBuilder clientBuilder = HttpClients.custom();
      clientBuilder = clientBuilder.setRoutePlanner(routePlanner);

      //Building a CloseableHttpClient
      CloseableHttpClient httpclient = clientBuilder.build();

      //Creating an HttpGet object
      HttpGet httpget = new HttpGet("/");

      //Executing the Get request
      HttpResponse httpresponse = httpclient.execute(targethost, httpget);

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());

      //Printing all the headers of the response
      Header[] headers = httpresponse.getAllHeaders();
 
      for (int i = 0; i < headers.length; i++) {
         System.out.println(headers[i]);
      }
      
      //Printing the body of the response
      HttpEntity entity = httpresponse.getEntity();

      if (entity != null) {
         System.out.println(EntityUtils.toString(entity));
      }
   }
}

Output

On executing, the above program generates the following output −

HTTP/1.1 200 OK
Date: Sun, 23 Dec 2018 10:21:47 GMT
Server: Apache/2.4.9 (Win64) PHP/5.5.13
Last-Modified: Tue, 24 Jun 2014 10:46:24 GMT
ETag: "2e-4fc92abc3c000"
Accept-Ranges: bytes
Content-Length: 46
Content-Type: text/html
<html><body><h1>It works!</h1></body></html>

Apache HttpClient - Proxy Authentication

In this chapter, we will learn how to create a HttpRequest authenticated using username and password and tunnel it through a proxy to a target host, using an example.

Step 1 - Create a CredentialsProvider object

The CredentialsProvider Interface maintains a collection to hold the user login credentials. You can create its object by instantiating the BasicCredentialsProvider class, the default implementation of this interface.

CredentialsProvider credentialsPovider = new BasicCredentialsProvider();

Step 2 - Set the credentials

You can set the required credentials to the CredentialsProvider object using the setCredentials() method. This method accepts two objects −

  • AuthScope object − Authentication scope specifying the details like hostname, port number, and authentication scheme name.

  • Credentials object − Specifying the credentials (username, password). Set the credentials using the setCredentials() method for both host and proxy as shown below.

credsProvider.setCredentials(new AuthScope("example.com", 80), new
   UsernamePasswordCredentials("user", "mypass"));
credsProvider.setCredentials(new AuthScope("localhost", 8000), new
   UsernamePasswordCredentials("abc", "passwd"));

Step 3 - Create an HttpClientBuilder object

Create a HttpClientBuilder using the custom() method of the HttpClients class as shown below −

//Creating the HttpClientBuilder
HttpClientBuilder clientbuilder = HttpClients.custom();

Step 4 - Set the CredentialsProvider

You can set the CredentialsProvider object to a HttpClientBuilder object using the setDefaultCredentialsProvider() method. Pass the previously created CredentialsProvider object to this method.

clientbuilder = clientbuilder.setDefaultCredentialsProvider(credsProvider);

Step 5 - Build the CloseableHttpClient

Build the CloseableHttpClient object using the build() method.

CloseableHttpClient httpclient = clientbuilder.build();

Step 6 - Create the proxy and target hosts

Create the target and proxy hosts by instantiating the HttpHost class.

//Creating the target and proxy hosts
HttpHost target = new HttpHost("example.com", 80, "http");
HttpHost proxy = new HttpHost("localhost", 8000, "http");

Step 7 - Set the proxy and build a RequestConfig object

Create a RequestConfig.Builder object using the custom() method. Set the previously created proxyHost object to the RequestConfig.Builder using the setProxy() method. Finally, build the RequestConfig object using the build() method.

RequestConfig.Builder reqconfigconbuilder= RequestConfig.custom();
reqconfigconbuilder = reqconfigconbuilder.setProxy(proxyHost);
RequestConfig config = reqconfigconbuilder.build();

Step 8 - Create a HttpGet request object and set config object to it.

Create a HttpGet object by instantiating the HttpGet class. Set the config object created in the previous step to this object using the setConfig() method.

//Create the HttpGet request object
HttpGet httpGet = new HttpGet("/");

//Setting the config to the request
httpget.setConfig(config);

Step 9 - Execute the request

Execute the request by passing the HttpHost object (target) and request (HttpGet) as parameters to the execute() method.

HttpResponse httpResponse = httpclient.execute(targetHost, httpget);

Example

Following example demonstrates how to execute a HTTP request through a proxy using username and password.

import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;

public class ProxyAuthenticationExample {
   public static void main(String[] args) throws Exception {

      //Creating the CredentialsProvider object
      CredentialsProvider credsProvider = new BasicCredentialsProvider();

      //Setting the credentials
      credsProvider.setCredentials(new AuthScope("example.com", 80), 
         new UsernamePasswordCredentials("user", "mypass"));
      credsProvider.setCredentials(new AuthScope("localhost", 8000), 
         new UsernamePasswordCredentials("abc", "passwd"));

      //Creating the HttpClientBuilder
      HttpClientBuilder clientbuilder = HttpClients.custom();

      //Setting the credentials
      clientbuilder = clientbuilder.setDefaultCredentialsProvider(credsProvider);
      
      //Building the CloseableHttpClient object
      CloseableHttpClient httpclient = clientbuilder.build();


      //Create the target and proxy hosts
      HttpHost targetHost = new HttpHost("example.com", 80, "http");
      HttpHost proxyHost = new HttpHost("localhost", 8000, "http");

      //Setting the proxy
      RequestConfig.Builder reqconfigconbuilder= RequestConfig.custom();
      reqconfigconbuilder = reqconfigconbuilder.setProxy(proxyHost);
      RequestConfig config = reqconfigconbuilder.build();

      //Create the HttpGet request object
      HttpGet httpget = new HttpGet("/");

      //Setting the config to the request
      httpget.setConfig(config);
 
      //Printing the status line
      HttpResponse response = httpclient.execute(targetHost, httpget);
      System.out.println(response.getStatusLine());

   }
}

Output

On executing, the above program generates the following output −

HTTP/1.1 200 OK

Apache HttpClient - Form-Based Login

Using the HttpClient library you can send a request or, login to a form by passing parameters.

Follow the steps given below to login to a form.

Step 1 - Create an HttpClient object

The createDefault() method of the HttpClients class returns an object of the class CloseableHttpClient, which is the base implementation of the HttpClient interface. Using this method, create an HttpClient object −

CloseableHttpClient httpClient = HttpClients.createDefault();

Step 2 - Create a RequestBuilder object

The class RequestBuilder is used to build request by adding parameters to it. If the request type is PUT or POST, it adds the parameters to the request as URL encoded entity

Create a RequestBuilder object (of type POST) using the post() method.

//Building the post request object
RequestBuilder reqbuilder = RequestBuilder.post();

Step 3 - Set Uri and parameters to the RequestBuilder.

Set the URI and parameters to the RequestBuilder object using the setUri() and addParameter() methods of the RequestBuilder class.

//Set URI and parameters
RequestBuilder reqbuilder = reqbuilder.setUri("http://httpbin.org/post");
reqbuilder = reqbuilder1.addParameter("Name", "username").addParameter("password", "password");

Step 4 - Build the HttpUriRequest object

After setting the required parameters, build the HttpUriRequest object using the build() method.

//Building the HttpUriRequest object
HttpUriRequest httppost = reqbuilder2.build();

Step 5 - Execute the request

The execute method of the CloseableHttpClient object accepts a HttpUriRequest (interface) object (i.e. HttpGet, HttpPost, HttpPut, HttpHead etc.) and returns a response object.

Execute the HttpUriRequest created in the previous steps by passing it to the execute() method.

//Execute the request
HttpResponse httpresponse = httpclient.execute(httppost);

Example

Following example demonstrates how to logon to a form by sending login credentials. Here, we have sent two parameters − username and password to a form and tried to print the message entity and status of the request.

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.methods.RequestBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import java.io.IOException;
import java.net.URISyntaxException;

public class FormLoginExample {
 
   public static void main(String args[]) throws Exception {

      //Creating CloseableHttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();
 
      //Creating the RequestBuilder object
      RequestBuilder reqbuilder = RequestBuilder.post();

      //Setting URI and parameters
      RequestBuilder reqbuilder1 = reqbuilder.setUri("http://httpbin.org/post");
      RequestBuilder reqbuilder2 = reqbuilder1.addParameter("Name", 
         "username").addParameter("password", "password");

      //Building the HttpUriRequest object
      HttpUriRequest httppost = reqbuilder2.build();

      //Executing the request
      HttpResponse httpresponse = httpclient.execute(httppost);

      //Printing the status and the contents of the response
      System.out.println(EntityUtils.toString(httpresponse.getEntity()));
      System.out.println(httpresponse.getStatusLine());
   }
}

Output

On executing, the above program generates the following output −

{
   "args": {},
   "data": "",
   "files": {},
   "form": {
      "Name": "username",
      "password": "password"
   },
   "headers": {
      "Accept-Encoding": "gzip,deflate",
      "Connection": "close",
      "Content-Length": "31",
      "Content-Type": "application/x-www-form-urlencoded; charset = UTF-8",
      "Host": "httpbin.org",
      "User-Agent": "Apache-HttpClient/4.5.6 (Java/1.8.0_91)"
   },
   "json": null,
   "origin": "117.216.245.180",
   "url": "http://httpbin.org/post"
}
HTTP/1.1 200 OK

Form Login with Cookies

If your form stores cookies, instead of creating default CloseableHttpClient object.

Create a CookieStore object by instantiating the BasicCookieStore class.

//Creating a BasicCookieStore object
BasicCookieStore cookieStore = new BasicCookieStore();

Create a HttpClientBuilder using the custom() method of the HttpClients class.

//Creating an HttpClientBuilder object
HttpClientBuilder clientbuilder = HttpClients.custom();

Set the cookie store to the client builder using the setDefaultCookieStore() method.

//Setting default cookie store to the client builder object
Clientbuilder = clientbuilder.setDefaultCookieStore(cookieStore);

Build the CloseableHttpClient object using the build() method.

//Building the CloseableHttpClient object
CloseableHttpClient httpclient = clientbuilder1.build();

Build the HttpUriRequest object as specified above by passing execute the request.

If the page stores cookies, the parameters you have passed will be added to the cookie store.

You can print the contents of the CookieStore object where you can see your parameters (along with the previous ones the page stored in case).

To print the cookies, get all the cookies from the CookieStore object using the getCookies() method. This method returns a List object. Using Iterator, print the list objects contents as shown below −

//Printing the cookies
List list = cookieStore.getCookies();

System.out.println("list of cookies");
Iterator it = list.iterator();
if(it.hasNext()) {
   System.out.println(it.next());
}

Apache HttpClient - Cookies Management

Cookies are text files stored on the client computer and they are kept for various information tracking purpose.

HttpClient provides support for cookies you can create and manage cookies.

Creating a cookie

Follow the steps given below to create a cookie using HttpClient library.

Step 1 - Create Cookiestore object

The CookieStore interface represents the abstract store for Cookie objects. You can create a cookie store by instantiating the BasicCookieStore class, a default implementation of this interface.

//Creating the CookieStore object
CookieStore cookieStore = new BasicCookieStore();

Step 2 - Create ClientCookie object

In addition to the functionalities of a cookie, ClientCookie can get the original cookies in the server. You can create a client cookie by instantiating the BasicClientCookie class. To the constructor of this class, you need to pass the key-value pair that you desired to store in that particular cookie.

//Creating client cookie
BasicClientCookie clientCookie = new BasicClientCookie("name","Raju");

Step 3 - Set values to the cookie

To a client cookie, you can set/remove path, value, version, expiry date, domain, comment, and attribute using the respective methods.

Calendar myCal = new GregorianCalendar(2018, 9, 26);
Date expiryDate = myCal.getTime();
clientcookie.setExpiryDate(expiryDate);
clientcookie.setPath("/");
clientcookie.setSecure(true);
clientcookie.setValue("25");
clientcookie.setVersion(5);

Step 4 - Add cookie to the cookie store

You can add cookies to the cookie store using the addCookie() method of the BasicCookieStore class.

Add the required cookies to the Cookiestore.

//Adding the created cookies to cookie store
cookiestore.addCookie(clientcookie);

Example

Following example demonstrates how to create cookies and add them to a cookie store. Here, we created a cookie store, a bunch of cookies by setting the domain and path values, and added these to the cookie store.

import org.apache.http.client.CookieStore;
import org.apache.http.impl.client.BasicCookieStore;
import org.apache.http.impl.cookie.BasicClientCookie;

public class CookieHandlingExample {
   
   public static void main(String args[]) throws Exception{
      
      //Creating the CookieStore object
      CookieStore cookiestore = new BasicCookieStore();
 
      //Creating client cookies
      BasicClientCookie clientcookie1 = new BasicClientCookie("name","Raju");
      BasicClientCookie clientcookie2 = new BasicClientCookie("age","28");
      BasicClientCookie clientcookie3 = new BasicClientCookie("place","Hyderabad");

      //Setting domains and paths to the created cookies
      clientcookie1.setDomain(".sample.com");
      clientcookie2.setDomain(".sample.com");
      clientcookie3.setDomain(".sample.com");

      clientcookie1.setPath("/");
      clientcookie2.setPath("/");
      clientcookie3.setPath("/");
 
      //Adding the created cookies to cookie store
      cookiestore.addCookie(clientcookie1);
      cookiestore.addCookie(clientcookie2);
      cookiestore.addCookie(clientcookie3);
   }
}

Retrieving a cookie

You can get the cookies added to a cookie store using getCookies() method of the asicCookieStore class. This method returns a list which holds all the cookies in the cookie store.

You can print the contents of a cookie store using the Iterator as shown below −

//Retrieving the cookies
List list = cookieStore.getCookies();

//Creating an iterator to the obtained list
Iterator it = list.iterator();
while(it.hasNext()) {
   System.out.println(it.next());
}

Example

Following example demonstrates how to retrieve cookies from a cookie store. Here, we are adding a bunch of cookies to a cookie store and retrieving them back.

import org.apache.http.client.CookieStore;
import org.apache.http.impl.client.BasicCookieStore;
import org.apache.http.impl.cookie.BasicClientCookie;

public class CookieHandlingExample {
 
   public static void main(String args[]) throws Exception{
      
      //Creating the CookieStore object
      CookieStore cookiestore = new BasicCookieStore();
      
      //Creating client cookies
      BasicClientCookie clientcookie1 = new BasicClientCookie("name","Raju");
      BasicClientCookie clientcookie2 = new BasicClientCookie("age","28");
      BasicClientCookie clientcookie3 = new BasicClientCookie("place","Hyderabad");

      //Setting domains and paths to the created cookies
      clientcookie1.setDomain(".sample.com");
      clientcookie2.setDomain(".sample.com");
      clientcookie3.setDomain(".sample.com");

      clientcookie1.setPath("/");
      clientcookie2.setPath("/");
      clientcookie3.setPath("/");
 
      //Adding the created cookies to cookie store
      cookiestore.addCookie(clientcookie1);
      cookiestore.addCookie(clientcookie2);
      cookiestore.addCookie(clientcookie3);
   }
}

Output

On executing, this program generates the following output −

[version: 0][name: age][value: 28][domain: .sample.com][path: /][expiry: null]
[version: 0][name: name][value: Raju][domain: my.example.com][path: /][expiry:
null]
[version: 0][name: place][value: Hyderabad][domain: .sample.com][path:
/][expiry: null]

Apache HttpClient - Multiple Threads

A multi-threaded program contains two or more parts that can run concurrently and each part can handle a different task at the same time making optimal use of the available resources.

You can execute requests from multiple threads by writing a multithreaded HttpClient program.

If you want to execute multiple client requests from threads consecutively, you need to create a ClientConnectionPoolManager. It maintains a pool of HttpClientConnections and serves multiple requests from threads.

The connections manager pools the connections based on the route. If the manager has connections for a particular route, then it serves new requests in those routes by leasing an existing connection from the pool, instead of creating a new one.

Follow the steps to execute requests from multiple threads −

Step 1 - Creating the Client Connection Pool Manager

Create the Client Connection Pool Manager by instantiating the PoolingHttpClientConnectionManager class.

PoolingHttpClientConnectionManager connManager = new
   PoolingHttpClientConnectionManager();

Step 2 - Set the maximum number of connections

Set the maximum number of connections in the pool using the setMaxTotal() method.

//Set the maximum number of connections in the pool
connManager.setMaxTotal(100);

Step 3 - Create a ClientBuilder Object

Create a ClientBuilder Object by setting the connection manager using the setConnectionManager() method as shown below −

HttpClientBuilder clientbuilder =
HttpClients.custom().setConnectionManager(connManager);

Step 4 - Create the HttpGet request objects

Instantiate the HttpGet class by passing the desired URI to its constructor as a parameter. 

HttpGet httpget1 = new HttpGet("URI1");
HttpGet httpget2 = new HttpGet("URI2");
. . . . . . . . . . . .

Step 5 - Implementing the run method

Make sure that you have created a class, made it a thread (either by extending the thread class or, by implementing the Runnable interface) and implemented the run method.

public class ClientMultiThreaded extends Thread {
   public void run() {
      //Run method implementation . . . . . . . . . .
   }
}

Step 6 - Create Thread objects

Create thread objects by instantiating the Thread class (ClientMultiThreaded) created above.

Pass a HttpClient object, respective HttpGet object and, an integer representing the ID to these threads.

ClientMultiThreaded thread1 = new ClientMultiThreaded(httpclient,httpget1, 1);
ClientMultiThreaded thread2 = new ClientMultiThreaded(httpclient,httpget2, 2);
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Step 7 - Start and join the threads

Start all the threads using start() method and join them using the join method().

thread1.start();
thread2.start();
. . . . . . . .
thread1.join();
thread2.join();
. . . . . . . . . . . .

Step 8 - Run method implementation

Within the run method, execute the request, retrieve the response and print the results.

Example

Following example demonstrates the execution of HTTP requests simultaneously from multiple threads. In this example, we are trying to execute various requests from various threads and trying to print the status, and the number of bytes read by each client.

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.util.EntityUtils;

public class ClientMultiThreaded extends Thread {
   CloseableHttpClient httpClient;
   HttpGet httpget;
   int id;
 
   public ClientMultiThreaded(CloseableHttpClient httpClient, HttpGet httpget,
   int id) {
      this.httpClient = httpClient;
      this.httpget = httpget;
      this.id = id;
   }
   @Override
   public void run() {
      try{
         //Executing the request
         CloseableHttpResponse httpresponse = httpClient.execute(httpget);

         //Displaying the status of the request.
         System.out.println("status of thread "+id+":"+httpresponse.getStatusLine());

         //Retrieving the HttpEntity and displaying the no.of bytes read
         HttpEntity entity = httpresponse.getEntity();
         if (entity != null) {
            System.out.println("Bytes read by thread thread "+id+":
               "+EntityUtils.toByteArray(entity).length);
         }
      }catch(Exception e) {
         System.out.println(e.getMessage());
      }
   }
      
   public static void main(String[] args) throws Exception {

      //Creating the Client Connection Pool Manager by instantiating the PoolingHttpClientConnectionManager class.
      PoolingHttpClientConnectionManager connManager = new PoolingHttpClientConnectionManager();

      //Set the maximum number of connections in the pool
      connManager.setMaxTotal(100);

      //Create a ClientBuilder Object by setting the connection manager
      HttpClientBuilder clientbuilder = HttpClients.custom().setConnectionManager(connManager);
 
      //Build the CloseableHttpClient object using the build() method.
      CloseableHttpClient httpclient = clientbuilder.build();

      //Creating the HttpGet requests
      HttpGet httpget1 = new HttpGet("http://www.howcodex.com/");
      HttpGet httpget2 = new HttpGet("http://www.google.com/");
      HttpGet httpget3 = new HttpGet("https://www.qries.com/");
      HttpGet httpget4 = new HttpGet("https://in.yahoo.com/");
 
      //Creating the Thread objects
      ClientMultiThreaded thread1 = new ClientMultiThreaded(httpclient,httpget1, 1);
      ClientMultiThreaded thread2 = new ClientMultiThreaded(httpclient,httpget2, 2);
      ClientMultiThreaded thread3 = new ClientMultiThreaded(httpclient,httpget3, 3);
      ClientMultiThreaded thread4 = new ClientMultiThreaded(httpclient,httpget4, 4);

      //Starting all the threads
      thread1.start();
      thread2.start();
      thread3.start();
      thread4.start();

      //Joining all the threads
      thread1.join();
      thread2.join();
      thread3.join();
      thread4.join();
   }
}

Output

On executing, the above program generates the following output −

status of thread 1: HTTP/1.1 200 OK
Bytes read by thread thread 1: 36907
status of thread 2: HTTP/1.1 200 OK
Bytes read by thread thread 2: 13725
status of thread 3: HTTP/1.1 200 OK
Bytes read by thread thread 3: 17319
status of thread 4: HTTP/1.1 200 OK
Bytes read by thread thread 4: 127018

Apache HttpClient - Custom SSL Context

Using Secure Socket Layer, you can establish a secured connection between the client and server. It helps to safeguard sensitive information such as credit card numbers, usernames, passwords, pins, etc.

You can make connections more secure by creating your own SSL context using the HttpClient library.

Follow the steps given below to customize SSLContext using HttpClient library −

Step 1 - Create SSLContextBuilder object

SSLContextBuilder is the builder for the SSLContext objects. Create its object using the custom() method of the SSLContexts class.

//Creating SSLContextBuilder object
SSLContextBuilder SSLBuilder = SSLContexts.custom();

Step 2 - Load the Keystore

In the path Java_home_directory/jre/lib/security/, you can find a file named cacerts. Save this as your key store file (with extension .jks). Load the keystore file and, its password (which is changeit by default) using the loadTrustMaterial() method of the SSLContextBuilder class.

//Loading the Keystore file
File file = new File("mykeystore.jks");
SSLBuilder = SSLBuilder.loadTrustMaterial(file, "changeit".toCharArray());

Step 3 - build an SSLContext object

An SSLContext object represents a secure socket protocol implementation. Build an SSLContext using the build() method.

//Building the SSLContext
SSLContext sslContext = SSLBuilder.build();

Step 4 - Creating SSLConnectionSocketFactory object

SSLConnectionSocketFactory is a layered socket factory for TSL and SSL connections. Using this, you can verify the Https server using a list of trusted certificates and authenticate the given Https server.

You can create this in many ways. Depending on the way you create an SSLConnectionSocketFactory object, you can allow all hosts, allow only self-signed certificates, allow only particular protocols, etc.

To allow only particular protocols, create SSLConnectionSocketFactory object by passing an SSLContext object, string array representing the protocols need to be supported, string array representing the cipher suits need to be supported and a HostnameVerifier object to its constructor.

new SSLConnectionSocketFactory(sslcontext, new String[]{"TLSv1"}, null,    
   SSLConnectionSocketFactory.getDefaultHostnameVerifier());

To allow all hosts, create SSLConnectionSocketFactory object by passing a SSLContext object and a NoopHostnameVerifier object.

//Creating SSLConnectionSocketFactory SSLConnectionSocketFactory object
SSLConnectionSocketFactory sslConSocFactory = new SSLConnectionSocketFactory(sslcontext, new NoopHostnameVerifier());

Step 5 - Create an HttpClientBuilder object

Create an HttpClientBuilder object using the custom() method of the HttpClients class.

//Creating HttpClientBuilder
HttpClientBuilder clientbuilder = HttpClients.custom();

Step 6 - Set the SSLConnectionSocketFactory object

Set the SSLConnectionSocketFactory object to the HttpClientBuilder using the setSSLSocketFactory() method.

//Setting the SSLConnectionSocketFactory
clientbuilder = clientbuilder.setSSLSocketFactory(sslConSocFactory);

Step 7 - Build the CloseableHttpClient object

Build the CloseableHttpClient object by calling the build() method.

//Building the CloseableHttpClient
CloseableHttpClient httpclient = clientbuilder.build();

Step 8 - Create an HttpGet object

The HttpGet class represents the HTTP GET request which retrieves the information of the given server using a URI.

Create a HTTP GET request by instantiating the HttpGet class by passing a string representing the URI.

//Creating the HttpGet request
HttpGet httpget = new HttpGet("https://example.com/");

Step 9 - Execute the request

Execute the request using the execute() method.

//Executing the request
HttpResponse httpresponse = httpclient.execute(httpget);

Example

Following example demonstrates the customization of the SSLContrext −

import java.io.File;
import javax.net.ssl.SSLContext;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.conn.ssl.NoopHostnameVerifier;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.ssl.SSLContextBuilder;
import org.apache.http.ssl.SSLContexts;
import org.apache.http.util.EntityUtils;

public class ClientCustomSSL {
   
   public final static void main(String[] args) throws Exception {

      //Creating SSLContextBuilder object
      SSLContextBuilder SSLBuilder = SSLContexts.custom();
  
      //Loading the Keystore file
      File file = new File("mykeystore.jks");
      SSLBuilder = SSLBuilder.loadTrustMaterial(file,
         "changeit".toCharArray());

      //Building the SSLContext usiong the build() method
      SSLContext sslcontext = SSLBuilder.build();
 
      //Creating SSLConnectionSocketFactory object
      SSLConnectionSocketFactory sslConSocFactory = new SSLConnectionSocketFactory(sslcontext, new NoopHostnameVerifier());
 
      //Creating HttpClientBuilder
      HttpClientBuilder clientbuilder = HttpClients.custom();

      //Setting the SSLConnectionSocketFactory
      clientbuilder = clientbuilder.setSSLSocketFactory(sslConSocFactory);

      //Building the CloseableHttpClient
      CloseableHttpClient httpclient = clientbuilder.build();
      
      //Creating the HttpGet request
      HttpGet httpget = new HttpGet("https://example.com/");
 
      //Executing the request
      HttpResponse httpresponse = httpclient.execute(httpget);

      //printing the status line
      System.out.println(httpresponse.getStatusLine());

      //Retrieving the HttpEntity and displaying the no.of bytes read
      HttpEntity entity = httpresponse.getEntity();
      if (entity != null) {
         System.out.println(EntityUtils.toByteArray(entity).length);
      } 
   }
}

Output

On executing, the above program generates the following output.

HTTP/1.1 200 OK
1270

Apache HttpClient - Multipart Upload

Using HttpClient, we can perform Multipart upload, i.e., we can upload larger objects in smaller parts. In this chapter, we demonstrate the multipart upload in HTTP client by uploading a simple text file.

In general, any multipart upload contains three parts.

  • Initiation of the upload

  • Uploading the object parts

  • Completing the Multipart upload

For the multipart upload using HttpClient, we need to follow the below steps −

  • Create a multipart builder.

  • Add desired parts to it.

  • Complete the build and obtain a multipart HttpEntity.

  • Build request by setting the above muti-part entity.

  • Execute the request.

Following are the steps to upload a multipart entity using the HttpClient library.

Step 1 - Create an HttpClient object

The createDefault() method of the HttpClients class returns an object of the class CloseableHttpClient, which is the base implementation of the HttpClient interface. Using this method, create an HttpClient object −

//Creating CloseableHttpClient object
CloseableHttpClient httpclient = HttpClients.createDefault();

Step 2 - Create a FileBody object

FileBody class represents the binary body part backed by a file. Instantiate this class by passing a File object and a ContentType object representing the type of the content.

//Creating a File object
File file = new File("sample.txt");

//Creating the FileBody object
FileBody filebody = new FileBody(file, ContentType.DEFAULT_BINARY);

Step 3 - Create a MultipartEntityBuilder

The MultipartEntityBuilder class is used to build the multi-part HttpEntity object. Create its object using the create() method (of the same class).

//Creating the MultipartEntityBuilder
MultipartEntityBuilder entitybuilder = MultipartEntityBuilder.create();

Step 4 - Set the mode

A MultipartEntityBuilder has three modes: STRICT, RFC6532, and BROWSER_COMPATIBLE. Set it to the desired mode using the setMode() method.

//Setting the mode
entitybuilder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);

Step 5 - Add various the desired parts

Using the methods addTextBody(), addPart() and, addBinaryBody(), you can add simple text, files, streams, and other objects to a MultipartBuilder. Add the desired contents using these methods.

//Adding text
entitybuilder.addTextBody("sample_text", "This is the text part of our file");
//Adding a file
entitybuilder.addBinaryBody("image", new File("logo.png"));

Step 6 - Building single entity

You can build all these parts to a single entity using the build() method of the MultipartEntityBuilder class. Using this method, build all the parts into a single HttpEntity.

//Building a single entity using the parts
HttpEntity mutiPartHttpEntity = entityBuilder.build();

Step 7 - Create a RequestBuilder object

The class RequestBuilder is used to build request by adding parameters to it. If the request is of type PUT or POST, it adds the parameters to the request as URL encoded entity.

Create a RequestBuilder object (of type POST) using the post() method. And pass the Uri to which you wanted to send the request it as a parameter.

//Building the post request object
RequestBuilder reqbuilder = RequestBuilder.post("http://httpbin.org/post");

Step 8 - Set the entity object to the RequestBuilder

Set the above created multipart entity to the RequestBuilder using the setEntity() method of the RequestBuilder class.

//Setting the entity object to the RequestBuilder
reqbuilder.setEntity(mutiPartHttpEntity);

Step 9 - Build the HttpUriRequest

Build a HttpUriRequest request object using the build() method of the RequestBuilder class.

//Building the request
HttpUriRequest multipartRequest = reqbuilder.build();

Step 10 - Execute the request

Using the execute() method, execute the request built in the previous step (bypassing the request as a parameter to this method).

//Executing the request
HttpResponse httpresponse = httpclient.execute(multipartRequest);

Example

Following example demonstrates how to send a multipart request using the HttpClient library. In this example, we are trying to send a multipart request backed by a file.

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.methods.RequestBuilder;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.HttpMultipartMode;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import java.io.File;
import java.io.IOException;
import java.net.URISyntaxException;

public class MultipartUploadExample {
 
   public static void main(String args[]) throws Exception{

      //Creating CloseableHttpClient object
      CloseableHttpClient httpclient = HttpClients.createDefault();
 
      //Creating a file object
      File file = new File("sample.txt");

      //Creating the FileBody object
      FileBody filebody = new FileBody(file, ContentType.DEFAULT_BINARY);

      //Creating the MultipartEntityBuilder
      MultipartEntityBuilder entitybuilder = MultipartEntityBuilder.create();

      //Setting the mode
      entitybuilder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);

      //Adding text
      entitybuilder.addTextBody("sample_text", "This is the text part of our file");

      //Adding a file
      entitybuilder.addBinaryBody("image", new File("logo.png"));

      //Building a single entity using the parts
      HttpEntity mutiPartHttpEntity = entitybuilder.build();

      //Building the RequestBuilder request object
      RequestBuilder reqbuilder = RequestBuilder.post("http://httpbin.org/post");

      //Set the entity object to the RequestBuilder
      reqbuilder.setEntity(mutiPartHttpEntity);

      //Building the request
      HttpUriRequest multipartRequest = reqbuilder.build();

      //Executing the request
      HttpResponse httpresponse = httpclient.execute(multipartRequest);

      //Printing the status and the contents of the response
      System.out.println(EntityUtils.toString(httpresponse.getEntity()));
      System.out.println(httpresponse.getStatusLine());
   }
}

Output

On executing, the above program generates the following output −

{
   "args": {},
   "data": "",
   "files": {
      "image": "data:application/octets66PohrH3IWNk1FzpohfdXPIfv9X3490FGcuXsHn9X0piCwomF/xdgADZ9GsfSyvLYAAAAAE
      lFTkSuQmCC"
   },
   "form": {
      "sample_text": "This is the text part of our file"
   },
   "headers": {
      "Accept-Encoding": "gzip,deflate",
      "Connection": "close",
      "Content-Length": "11104", 
      "Content-Type": "multipart/form-data;
      boundary=UFJbPHT7mTwpVq70LpZgCi5I2nvxd1g-I8Rt",
      "Host": "httpbin.org",
      "User-Agent": "Apache-HttpClient/4.5.6 (Java/1.8.0_91)"
   },
   "json": null,
   "origin": "117.216.245.180",
   "url": "http://httpbin.org/post"
}
HTTP/1.1 200 OK
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