Struts 2 - Type Conversion

Advertisements

Previous Page
Next Page  

Everything on a HTTP request is treated as a String by the protocol. This includes numbers, booleans, integers, dates, decimals and everything else. However, in the Struts class, you could have properties of any data types.

How does Struts autowire the properties for you?

Struts uses a variety of type converters under the covers to do the heavy lifting.

For example, if you have an integer attribute in your Action class, Struts automatically converts the request parameter to the integer attribute without you doing anything. By default, Struts comes with a number of type converters

If you are using any of the below listed converters, then you have nothing to worry about −

  • Integer, Float, Double, Decimal
  • Date and Datetime
  • Arrays and Collections
  • Enumerations
  • Boolean
  • BigDecimal

At times when you are using your own data type, it is necessary to add your own converters to make Struts aware how to convert those values before displaying. Consider the following POJO class Environment.java.

package com.howcodex.struts2;

public class Environment {
   private String name;
   
   public  Environment(String name) {
      this.name = name;
   }
   
   public String getName() {
      return name;
   }
   
   public void setName(String name) {
      this.name = name;
   }
}

This is a very simple class that has an attribute called name, so nothing special about this class. Let us create another class that contains information about the system -SystemDetails.java.

For the purpose of this exercise, I have hardcoded the Environment to "Development" and the Operating System to "Windows XP SP3".

In a real-time project, you would get this information from the system configuration.

Let us have the following action class −

package com.howcodex.struts2;
import com.opensymphony.xwork2.ActionSupport;

public class SystemDetails extends ActionSupport {
   private Environment environment = new Environment("Development");
   private String operatingSystem = "Windows XP SP3";

   public String execute() {
      return SUCCESS;
   }
   
   public Environment getEnvironment() {
      return environment;
   }
   
   public void setEnvironment(Environment environment) {
      this.environment = environment;
   }
   
   public String getOperatingSystem() {
      return operatingSystem;
   }
   
   public void setOperatingSystem(String operatingSystem) {
      this.operatingSystem = operatingSystem;
   }
}

Next, let us create a simple JSP file System.jsp to display the Environment and the Operating System information.

<%@ page language = "java" contentType = "text/html; charset = ISO-8859-1"
pageEncoding = "ISO-8859-1"%>
<%@ taglib prefix = "s" uri = "/struts-tags"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
   "http://www.w3.org/TR/html4/loose.dtd">

<html>
   <head>
      <title>System Details</title>
   </head>
   
   <body>
      Environment: <s:property value = "environment"/><br/>
      Operating System:<s:property value = "operatingSystem"/>
   </body>
</html>

Let us wire the system.jsp and the SystemDetails.java class together using struts.xml.

The SystemDetails class has a simple execute () method that returns the string "SUCCESS".

<?xml version = "1.0" Encoding = "UTF-8"?>
<!DOCTYPE struts PUBLIC
   "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
   "http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>
   <constant name = "struts.devMode" value = "true" />
   <package name = "helloworld" extends = "struts-default">
      
      <action name = "system" 
            class = "com.howcodex.struts2.SystemDetails" 
            method = "execute">
         <result name = "success">/System.jsp</result>
      </action>
   </package>
</struts>

  • Right click on the project name and click Export > WAR File to create a War file.

  • Then deploy this WAR in the Tomcat's webapps directory.

  • Finally, start Tomcat server and try to access URL http://localhost:8080/HelloWorldStruts2/system.action. This will produce the following screen −

System Info

What is wrong with the above output? Struts knows how to display and convert the string "Windows XP SP3" and other built-in data types, but it does not know what to do with the property of Environment type. It is simply called toString() method on the class

To resolve this problem, let us now create and register a simple TypeConverter for the Environment class.

Create a class called EnvironmentConverter.java with the following.

package com.howcodex.struts2;

import java.util.Map;
import org.apache.struts2.util.StrutsTypeConverter;

public class EnvironmentConverter extends StrutsTypeConverter {
   @Override
   public Object convertFromString(Map context, String[] values, Class clazz) {
      Environment env = new Environment(values[0]);
      return env;
   }

   @Override
   public String convertToString(Map context, Object value) {
      Environment env  = (Environment) value;
      return env == null ? null : env.getName();
   }	
}

The EnvironmentConverter extends the StrutsTypeConverter class and tells Struts how to convert Environment to a String and vice versa by overriding two methods which are convertFromString() and convertToString().

Let us now register this converter before we use it in our application. There are two ways to register a converter.

If the converter will be used only in a particular action, then you would have to create a property file which needs to be named as '[action-class]'converstion.properties.

In our case, we create a file called SystemDetails-converstion.properties with the following registration entry −

environment = com.howcodex.struts2.EnvironmentConverter

In the above example, "environment" is the name of the property in the SystemDetails.java class and we are telling Struts to use the EnvironmentConverter for converting to and from this property.

However, we are not going to do this, Instead we are going to register this converter globally, so that it can be used throughout the application. To do this, create a property file called xwork-conversion.properties in the WEBINF/classes folder with the following line

com.howcodex.struts2.Environment = \
   com.howcodex.struts2.EnvironmentConverter

This simply registers the converter globally, so that Struts can automatically do the conversion every time when it encounters an object of the type Environment. Now, if you re-compiling and re-running the program, then you will get a better output as follows −

System Info

Obviously, now the result will be better which means our Struts convertor is working fine.

This is how you can create multiple convertors and register them to use as per your requirements.

Advertisements