問題：如何取到append操作後的集合

  <s:set name="books" value="books"/>
  <s:append id="list">
  <s:param value="#books"/>
  <s:param value="#request.list"/>
  </s:append>
  <s:property value="@[email protected](#list)"/>
  <%
ArrayList<Book> books1=MyDb.getBooks();
request.setAttribute("newlist", books1);
%>
<s:iterator value="#request.newlist" id="book" status="s">
 

起因：學習Struts2框架過程中，有一個實驗要求用list集合模擬資料庫，執行append操作後想要呼叫靜態方法把新的集合賦給原來的集合，發現傳入的list並不是一個集合

起初，我以為Struts框架將兩個集合合併後會自動轉換為我傳入時的ArrayList，發現介面輸出為空時，我下斷除錯了一下

除錯情況如下：

結果是傳入的不是ArrayList，看來至少我學習用的2.1版本並沒有我想的這個功能。

通過toString方法得到返回的是AppendIteratorFilter這個類，顯然append標籤底層通過該類實現操作。

AppendIteratorFilter.java原始碼如下

/*
 * $Id$
 *
 * 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.util;

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

import com.opensymphony.xwork2.Action;


/**
 * A bean that takes several iterators and outputs them in sequence
 *
 * @see org.apache.struts2.components.AppendIterator
 * @see org.apache.struts2.views.jsp.iterator.AppendIteratorTag
 */
public class AppendIteratorFilter extends IteratorFilterSupport implements Iterator, Action {

    List iterators = new ArrayList();

    // Attributes ----------------------------------------------------
    List sources = new ArrayList();


    // Public --------------------------------------------------------
    public void setSource(Object anIterator) {
        sources.add(anIterator);
    }

    // Action implementation -----------------------------------------
    public String execute() {
        // Make source transformations
        for (int i = 0; i < sources.size(); i++) {
            Object source = sources.get(i);
            iterators.add(getIterator(source));
        }

        return SUCCESS;
    }

    // Iterator implementation ---------------------------------------
    public boolean hasNext() {
        if (iterators.size() > 0) {
            return (((Iterator) iterators.get(0)).hasNext());
        } else {
            return false;
        }
    }

    public Object next() {
        try {
            return ((Iterator) iterators.get(0)).next();
        } finally {
            if (iterators.size() > 0) {
                if (!((Iterator) iterators.get(0)).hasNext()) {
                    iterators.remove(0);
                }
            }
        }
    }

    public void remove() {
        throw new UnsupportedOperationException();
    }
}
 

發現next方法的實現很奇怪，把自己寫的靜態方法引數型別修改為AppendIteratorFilter再次除錯一下

((Iterator) iterators.get(0)).next()

就得到了合併後的結果，反覆除錯，就不難發現，append操作其實是通過合併兩個集合的iterator實現的

PS:在非iterator標籤AppendIteratorFilter呼叫next方法後(即本文中在append標籤後iterator標籤前)，會改變AppendIteratorFilter next指標，此時若再返回到jsp介面仍使用append標籤name屬性定義的集合進行遍歷操作會沒有輸出結果