Struts example source code file (MergeIterator.java)

This example Struts source code file (MergeIterator.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

arraylist, contextbean, io, iterator, list, logger, mergeiterator, mergeiterator, mergeiteratorfilter, mergeiteratorfilter, object, object, string, strutstag, the, util

The Struts MergeIterator.java source code

/*
 * $Id: MergeIterator.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 java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.apache.struts2.components.Param.UnnamedParametric;
import org.apache.struts2.util.MakeIterator;
import org.apache.struts2.util.MergeIteratorFilter;
import org.apache.struts2.views.annotations.StrutsTag;
import org.apache.struts2.views.annotations.StrutsTagAttribute;

import com.opensymphony.xwork2.util.ValueStack;
import com.opensymphony.xwork2.util.logging.Logger;
import com.opensymphony.xwork2.util.logging.LoggerFactory;

/**
 * <!-- START SNIPPET: javadoc -->
 * <p>Component for MergeIteratorTag, which job is to merge iterators and successive
 * call to the merged iterator will cause each merge iterator to have a chance to
 * expose its element, subsequently next call will allow 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).</P>
 *
 * <p>Internally the task are delegated to MergeIteratorFilter

 *
 * <p>Example if there are 3 lists being merged, each list have 3 entries, the following will
 * be the logic.</P>
 * <ol>
 *      <li>Display first element of the first list
 *      <li>Display first element of the second list
 *      <li>Display first element of the third list
 *      <li>Display second element of the first list
 *      <li>Display second element of the second list
 *      <li>Display second element of the third list
 *      <li>Display third element of the first list
 *      <li>Display thrid element of the second list
 *      <li>Display third element of the thrid list
 * </ol>
 * <!-- END SNIPPET: javadoc -->
 *
 * <!-- START SNIPPET: params -->
 * <ul>
 *          <li>id (String) - the id where the resultant merged iterator will be stored in the stack's context
 * </ul>
 * <!-- END SNIPPET: params -->
 *
 *
 * <!-- START SNIPPET: javacode -->
 * public class MergeIteratorTagAction extends ActionSupport {
 *
 *  private List myList1;
 *  private List myList2;
 *  private List myList3;
 *
 *  public List getMyList1() {
 *      return myList1;
 *  }
 *
 *  public List getMyList2() {
 *      return myList2;
 *  }
 *
 *  public List getMyList3() {
 *      return myList3;
 *  }
 *
 *
 *  public String execute() throws Exception {
 *
 *      myList1 = new ArrayList();
 *      myList1.add("1");
 *      myList1.add("2");
 *      myList1.add("3");
 *
 *      myList2 = new ArrayList();
 *      myList2.add("a");
 *      myList2.add("b");
 *      myList2.add("c");
 *
 *      myList3 = new ArrayList();
 *      myList3.add("A");
 *      myList3.add("B");
 *      myList3.add("C");
 *
 *      return "done";
 *  }
 * }
 * <!-- END SNIPPET: javacode -->
 *
 * <!-- START SNIPPET: example -->
 * <s:merge var="myMergedIterator1">
 *      <s:param value="%{myList1}" />
 *      <s:param value="%{myList2}" />
 *      <s:param value="%{myList3}" />
 * </s:merge>
 * <s:iterator value="%{#myMergedIterator1}">
 *      <s:property />
 * </s:iterator>
 * <!-- END SNIPPET: example -->
 *
 * <!-- START SNIPPET: description -->
 * This wil generate "1aA2bB3cC".
 * <!-- START SNIPPET: description -->
 *
 * @see org.apache.struts2.util.MergeIteratorFilter
 * @see org.apache.struts2.views.jsp.iterator.MergeIteratorTag
 *
 */
@StrutsTag(name="merge", tldTagClass="org.apache.struts2.views.jsp.iterator.MergeIteratorTag", description="Merge the values " +
                "of a list of iterators into one iterator")
public class MergeIterator extends ContextBean implements UnnamedParametric {

    private static final Logger LOG = LoggerFactory.getLogger(MergeIterator.class);

    private MergeIteratorFilter mergeIteratorFilter = null;
    private List _parameters;

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

    public boolean start(Writer writer) {

        mergeIteratorFilter = new MergeIteratorFilter();
        _parameters = new ArrayList();

        return super.start(writer);
    }

    public boolean end(Writer writer, String body) {

        for (Iterator parametersIterator = _parameters.iterator(); parametersIterator.hasNext(); ) {
            Object iteratorEntryObj = parametersIterator.next();
            if (! MakeIterator.isIterable(iteratorEntryObj)) {
                LOG.warn("param with value resolved as "+iteratorEntryObj+" cannot be make as iterator, it will be ignored and hence will not appear in the merged iterator");
                continue;
            }
            mergeIteratorFilter.setSource(MakeIterator.convert(iteratorEntryObj));
        }

        mergeIteratorFilter.execute();

        // if id exists, we put it in the stack's context
        putInContext(mergeIteratorFilter);

        mergeIteratorFilter = null;

        return super.end(writer, body);
    }

    @StrutsTagAttribute(description="The name where the resultant merged iterator will be stored in the stack's context")
    public void setVar(String var) {
        super.setVar(var);
    }

    // == UnnamedParametric interface implementation ---------------------
    public void addParameter(Object value) {
        _parameters.add(value);
    }
}