Struts example source code file (Push.java)

This example Struts source code file (Push.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Struts tags/keywords

component, example, example, io, push, push, string, string, strutstag, strutstagattribute, value, valuestack, valuestack, you

The Struts Push.java source code

/*
 * $Id: Push.java 651946 2008-04-27 13:41:38Z apetrelli $
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.struts2.components;

import java.io.Writer;

import org.apache.struts2.views.annotations.StrutsTag;
import org.apache.struts2.views.annotations.StrutsTagAttribute;

import com.opensymphony.xwork2.util.ValueStack;

/**
 * <!-- START SNIPPET: javadoc -->
 * <p>Push value on stack for simplified usage.

 * <!-- END SNIPPET: javadoc -->
 *
 * <!-- START SNIPPET: params -->
 * <ul>
 *      <li>value* (Object) - value to be pushed into the top of the stack
 * </ul>
 * <!-- END SNIPPET: params -->
 *
 *
 * <p/> Examples
 * <pre>
 * <!-- START SNIPPET: example1 -->
 * <s:push value="user">
 *     <s:propery value="firstName" />
 *     <s:propery value="lastName" />
 * </s:push>
 * <!-- END SNIPPET: example1 -->
 * </pre>
 *
 * <!-- START SNIPPET: example1description -->
 * Pushed user into the stack, and hence property tag could access user's properties
 * (firstName, lastName etc) since user is not at the top of the stack
 * <!-- END SNIPPET: example1description -->
 *
 * <pre>
 * <!-- START SNIPPET: example2 -->
 *  <s:push value="myObject">                              ----- (1)
 *       <s:bean name="jp.SomeBean" var="myBean"/>        ----- (2)
 *          <s:param name="myParam" value="top"/>        ----- (3)
 *       </s:bean>
 *   </s:push>
 * <!-- END SNIPPET: example2 -->
 * </pre>
 *
 * <pre>
 * <!-- START SNIPPET: example2description -->
 * when in (1), myObject is at the top of the stack
 * when in (2), jp.SomeBean is in the top of stack, also in stack's context with key myBean
 * when in (3), top will get the jp.SomeBean instance
 * <!-- END SNIPPET: example2description -->
 * </pre>
 *
 * <pre>
 * <!-- START SNIPPET: example3 -->
 * <s:push value="myObject">                                       ---(A)
 *    <s:bean name="jp.SomeBean" var="myBean"/>                   ---(B)
 *       <s:param name="myParam" value="top.mySomeOtherValue"/>  ---(C)
 *    </s:bean>
 * </s:push>
 * <!-- END SNIPPET: example3 -->
 * </pre>
 *
 * <pre>
 * <!-- START SNIPPET: example3description -->
 * when in (A), myObject is at the top of the stack
 * when in (B), jp.SomeBean is at the top of the stack, also in context with key myBean
 * when in (C), top refers to jp.SomeBean instance. so top.mySomeOtherValue would invoke SomeBean's mySomeOtherValue() method
 * <!-- END SNIPPET: example3description -->
 * </pre>
 *
 * <pre>
 * <!-- START SNIPPET: example4 -->
 * <s:push value="myObject">                                 ---- (i)
 *    <s:bean name="jp.SomeBean" var="myBean"/>             ---- (ii)
 *       <s:param name="myParam" value="[1].top"/>         -----(iii)
 *    </s:bean>
 * </s:push>
 * <!-- END SNIPPET: example4 -->
 * </pre>
 *
 * <pre>
 * <!-- START SNIPPET: example4description -->
 * when in (i), myObject is at the top of the stack
 * when in (ii), jp.SomeBean is at the top of the stack, followed by myObject
 * when in (iii), [1].top will returned top of the cut of stack starting from myObject, namely myObject itself
 * <!-- END SNIPPET: example4description -->
 * </pre>
 *
 */
@StrutsTag(name="push", tldTagClass="org.apache.struts2.views.jsp.PushTag", description="Push value on stack for simplified usage.")
public class Push extends Component {
    protected String value;
    protected boolean pushed;

    public Push(ValueStack stack) {
        super(stack);
    }

    public boolean start(Writer writer) {
        boolean result = super.start(writer);

        ValueStack stack = getStack();

        if (stack != null) {
            stack.push(findValue(value, "value", "You must specify a value to push on the stack. Example: person"));
            pushed = true;
        } else {
            pushed = false; // need to ensure push is assigned, otherwise we may have a leftover value
        }

        return result;
    }

    public boolean end(Writer writer, String body) {
        ValueStack stack = getStack();

        if (pushed && (stack != null)) {
            stack.pop();
        }

        return super.end(writer, body);
    }

    @StrutsTagAttribute(description="Value to push on stack", required=true)
    public void setValue(String value) {
        this.value = value;
    }
    
}