How to read parameters from web.xml in Struts2 action class

Details: Written by Nam Ha Minh; Last Updated on 31 July 2019 | Print Email

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Sometimes we need to retrieve values of parameters which are configured in web.xmlfile from our Struts action class. For example, we define a parameter named host in the web.xml file as follows:

<context-param>
	<param-name>host</param-name>
	<param-value>192.168.123.233</param-value>
</context-param>

To read this parameter from within an action class, it requires doing the following things:

- Make the action class implementing the org.apache.struts2.util.ServletContextAware interface.
- Implement the setServletContext() method to obtain reference of the ServletContext object which is passed by Struts (for any action class that implements the ServletContextAware interface).
- In action method, we can read value of any parameter defined in the web.xmllike this:
```
String host = (String) servletContext.getInitParameter("host"); 
```

Let’s see a complete example.

Code of the web.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
		http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
	id="WebApp_ID" version="3.0">
  	
  	<display-name>Struts2WebParam</display-name>
  	
  	<context-param>
  		<param-name>host</param-name>
  		<param-value>192.168.123.233</param-value>
  	</context-param>
  	
	<filter>
	  <filter-name>struts2</filter-name>
	  <filter-class>
	  	org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
	  </filter-class>
	</filter>
	
	<filter-mapping>
	  <filter-name>struts2</filter-name>
	   <url-pattern>/*</url-pattern>
	</filter-mapping>
</web-app>

Code of the Struts action class:

package net.codejava.struts;

import javax.servlet.ServletContext;

import org.apache.struts2.util.ServletContextAware;

import com.opensymphony.xwork2.ActionSupport;

public class MyAction extends ActionSupport implements ServletContextAware {
	private String host;
	private ServletContext servletContext;
	
	public String execute() {
		host = (String) servletContext.getInitParameter("host");
		System.out.println("host = " + host);
		return SUCCESS;
	}
	
	@Override
	public void setServletContext(ServletContext context) {
		this.servletContext = context;
	}
	
	public String getHost() {
		return this.host;
	}
}

Note that in this action class, we also declare a property named host along with its getter method, so that it can be accessed in the result page.

Code of the result JSP page:

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
	"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Result</title>
</head>
<body>
	<center>
		<h3>Host = ${host}</h3>
	</center>
</body>
</html>

Code of the struts.xml file:

<?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>
	<package name="Struts2WebParam" extends="struts-default">
		
		<action name="test" class="net.codejava.struts.MyAction">
			<result name="success">/Result.jsp</result>
		</action>

	</package>
</struts>

Output:

Here is the output when running the application at http://localhost:8080/Struts2WebParam/test:

test reading parameter from web.xml in struts action class

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.

Attachments:
Struts2WebParam.war	[Deployable WAR file]	3410 kB
Struts2WebParam.zip	[Eclipse project]	3413 kB