Jakarta Struts Cookbook

5.3. Using a List-Backed Form Property

Problem

You want to create and use a form property backed by a java.util.List. You want to be able to access the entire list of data through one method as well as specific values in the list using indexed properties.

Solution

Create the form property as an indexed property, backed by a java.util.List, as shown in Example 5-4.

Example 5-4. List-backed form property

package com.oreilly.strutsckbk.ch05;

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

import javax.servlet.http.HttpServletRequest;

import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionMapping;

public class ListForm extends ActionForm {
    
    private int size = 3;
    private List friends = new ArrayList(size);
    
    public List getFriends( ) { 
        return friends;
    }

    public String getFriend(int index) {
        return (String) friends.get(index);
    }

    public void setFriend(int index, String name) {
        friends.set(index, name);
    }
  
    public void reset(ActionMapping mapping, HttpServletRequest request) {
        // prepopulate the list with empty strings
        friends = new ArrayList( );
        for (int i=0; i<size;i++) friends.add("");
    }
}

Example 5-5 (list_form_test.jsp) shows how the property values can be accessed on a JSP page. The form is created by accessing individual elements as indexed properties. The results are output by iterating over the list.

Example 5-5. Accessing list-backed form properties

<%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib uri="http://jakarta.apache.org/struts/tags-html" ...