Ajax 動態清單

最新推荐文章于 2022-05-19 09:27:56 发布

最新推荐文章于 2022-05-19 09:27:56 发布 · 73 阅读

文章标签：

#Ajax #Servlet #XML #JavaScript #Spring #ViewUI

DynamicListeEx-1.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=BIG5">
<title>動態載入清單</title>
<script type="text/javascript" src=DynamicListEx-1.js></script>
</head>
<body>
    種類…
    <select id="type" onchange="refreshBooklList();">
        <option value="notTech">非關語言</option>
        <option value="language">語言技術</option>
        <option value="framework">開源框架</option>
    </select>

    <br/><br/>
    書籍…
    <br/>
    <select id="books" size="6" style="width:300px;">

    </select>
</body>
</html>

當使用者選擇完書籍種類之後，另一個選單就會自動填上符合該重類的書籍，來看看JavaScript如何撰寫：

DynamicListEx-1.js

var xmlHttp;

window.onload = refreshBooklList;

function createXMLHttpRequest() {
    if(window.XMLHttpRequest) {
        xmlHttp = new XMLHttpRequest();
    }
    else if(window.ActiveXObject) {
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
    }
}

function refreshBooklList() {
    var type = document.getElementById("type").value;
    var url = "RefreshBookServlet?type=" + type;

    createXMLHttpRequest();
    xmlHttp.onreadystatechange = handleStateChange;
    xmlHttp.open("GET", url);
    xmlHttp.send(null);
}

function handleStateChange() {
    if(xmlHttp.readyState == 4) {
        if(xmlHttp.status == 200) {
            clearBookList();
	    updateBookList();
        }
    }
}

// 清除上一次的顯示結果
function clearBookList() { 
    var books = document.getElementById("books");
    while(books.childNodes.length > 0) {
        books.removeChild(books.childNodes[0]);
    }
}

// 以回應更新資料
function updateBookList() {
    var results = xmlHttp.responseXML.getElementsByTagName("book");
    var books = document.getElementById("books");

    var option = null;
    for(var i = 0; i < results.length; i++) {
        option = document.createElement("option");
        option.appendChild(document.createTextNode(results[i].firstChild.nodeValue));
        books.appendChild(option);
    }
}

從伺服端要傳回以下的XML，表示根據種類的查詢結果：

<books>
<book>Java 學習筆記</book>
<book>C++ 學習筆記</book>
<book>JSP/Servlet 學習筆記</book>
<book>Ajax 學習筆記</book>
</books>

您可以使用以下這個簡單的Servlet模擬資料查詢並傳回XML回應的過程：

RefreshBookServlet.java

package onlyfun.caterpillar;
import java.util.*;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class RefreshBookServlet extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet {
    private static Map inMemoryDB = new HashMap();

    public void init() throws ServletException {
        inMemoryDB.put("notTech", 
                new String[] {"學習筆記", "電腦圖學", "常見程式演算", "設計模式"});
        inMemoryDB.put("language", 
                new String[] {"Java 學習筆記", "JSP/Servlet 學習筆記", "C++ 學習筆記", "Ajax 學習筆記"});
        inMemoryDB.put("framework", 
                new String[] {"Struts 學習筆記", "Spring 學習筆記", "Hibernate 學習筆記", "JUnit 學習筆記"});
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
                                    throws ServletException, IOException {
        String type = request.getParameter("type");

        StringBuffer xml = new StringBuffer("<books>");
        String[] books = (String[]) inMemoryDB.get(type);
        for(int i = 0; i < books.length; i++) {
            xml.append("<book>");
            xml.append(books[i]);
            xml.append("</book>");
        }
        xml.append("</books>");

        response.setCharacterEncoding("UTF8");     
        response.setContentType("text/xml");
        response.getWriter().write(xml.toString());
        response.getWriter().close();
    }  	
}