Dinesh on Java

Struts2

Struts 2 Merge Tag Example

In this section, we are going to describe the merge tag. The merge tag is a generic tag that is used to merge iterators. The successive call to the merge iterator causes each merge iterator to have a chance to expose its element, subsequently next call allows the next iterator to expose its element. Once the last iterator is done exposing its element, the first iterator is allowed to do so again (unless it is exhausted of entries).

In the current example, 3 lists being merged, each list have 3 entries, the following will be the logic.

Display first element of the first list.
Display first element of the second list.
Display first element of the third list.
Display second element of the first list.
Display second element of the second list.
Display second element of the third list.
Display third element of the first list.
Display third element of the second list
Display third element of the third list…..and so on..

Create action classes:
First of all let us create a simple class called ControlTagAction.java which looks like:

package com.dineshonjava.struts2.action;

import java.util.ArrayList;
import java.util.List;

import com.opensymphony.xwork2.ActionSupport;

/**
 * @author Dinesh Rajput
 *
 */
public class ControlTagAction extends ActionSupport{

 private static final long serialVersionUID = 1L;
 
 private List<String> myList1 = new ArrayList<String>();
 private List<String> myList2 = new ArrayList<String>();
 private List<String> myList3 = new ArrayList<String>();
 
 public String execute() {
  myList1.add("dinesh in list 1");
  myList1.add("aadesh in list 1");
  myList1.add("vinesh in list 1");
  
  myList2.add("dinesh in list 2");
  myList2.add("aadesh in list 2");
  myList1.add("vinesh in list 2");
  
  myList3.add("dinesh in list 3");
  myList3.add("aadesh in list 3");
  myList1.add("vinesh in list 3");
  
  
  return SUCCESS;
 }


 public List<String> getMyList1() {
  return myList1;
 }


 public void setMyList1(List<String> myList1) {
  this.myList1 = myList1;
 }


 public List<String> getMyList2() {
  return myList2;
 }


 public void setMyList2(List<String> myList2) {
  this.myList2 = myList2;
 }


 public List<String> getMyList3() {
  return myList3;
 }


 public void setMyList3(List<String> myList3) {
  this.myList3 = myList3;
 }

}

Create views
Create a file called merge.jsp with the following contents:

<%@ taglib prefix="s" uri="/struts-tags" %>

<html>
  <head>
  <title>Merge Control Tag Struts2 | dineshonjava.com</title>
  </head>
  <body>
  <h1><span style="background-color: #FFFFcc">Merge Tag Example! | dineshonjava.com
</span></h1>
  <s:merge id="mergeId">
  <s:param value="%{myList1}" />
  <s:param value="%{myList2}" />
  <s:param value="%{myList3}" />
  </s:merge>
  <s:iterator value="%{#mergeId}">
  <s:property /><br>
  </s:iterator>
  </body>
</html>

The merge tag takes two or more lists as parameters.

Configuration Files
Your struts.xml should look like:

<?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.enable.DynamicMethodInvocation" value="false" />
    <constant name="struts.devMode" value="false" />
    <constant name="struts.custom.i18n.resources" value="myapp" />
 
    <package name="default" extends="struts-default" namespace="/">
        <action name="mergetag" class="com.dineshonjava.struts2.action.ControlTagAction">
            <result name="success">/merge.jsp</result>
        </action>
        
    </package>
 </struts>

Your web.xml should look like:

<?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>Struts2ControlTags</display-name>
  <filter>
        <filter-name>struts2</filter-name>
        <filter-class>
            org.apache.struts2.dispatcher.FilterDispatcher
        </filter-class>
    </filter>
    <filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

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/doj/mergetag.

This will give you following screen:

Download Source Code
Struts2AppendTag.zip

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!