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DWR JavaScript HTML Ajax

假設您要從資料庫中查詢出一些字串，然後填寫到表單的下拉選單中。

例如一個示意的Java程式如下：
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package onlyfun.caterpillar;

public class Option {
 public String[] getOptions() {
 // 實際上這些字串是從資料庫中查到的啦…
 return new String[] {"良葛格", "毛美眉", "米小狗"};
 }
}

傳回的字串陣列，您要填寫到下拉選單中，當然，首先我們要在dwr.xml中開發這個物件…
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 1.0//EN" "http://www.getahead.ltd.uk/dwr/dwr10.dtd">

<dwr>
 <allow>
 <create creator="new" javascript="OPT">
 <param name="class" value="onlyfun.caterpillar.Option"/>
 </create>
 </allow>
</dwr>

這是我們的網頁…
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=BIG5">
<script src="option.js" type="text/javascript"></script>
<script src="dwr/interface/OPT.js" type="text/javascript"></script>
<script src="dwr/engine.js" type="text/javascript"></script>
<script src="dwr/util.js" type="text/javascript"></script>

</head>

<body>
 選項: <select id="opts"></select>
</body>
</html>

傳回的字串陣列會填入opts這個select中，我們的option.js如下…
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window.onload = function() {
 OPT.getOptions(populate);
};

function populate(list){
 DWRUtil.removeAllOptions("opts");
 DWRUtil.addOptions("opts", list);
}

夠簡單了…不需要解釋了…

看一下結果…

好啦！我知道有人在說了，這個程式有夠無聊…

改一下！就是個不錯的範例了，例如連動方塊，唔！在Ajax in action中叫啥？Dynamic double combo？…

假設一個會去從資料庫中查詢資料的Java程式示意如下：
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package onlyfun.caterpillar;

import java.util.Map;
import java.util.TreeMap;

public class Bike {
 private Map<String, String[]> bikes;

 public Bike() {
 bikes = new TreeMap<String, String[]>();
 bikes.put("2000", new String[] {"2000 T1", "2000 T2", "2000 T3"});
 bikes.put("2001", new String[] {"2001 A1", "2001 A2"});
 bikes.put("2002", new String[] {"2002 BW1", "2002 BW2", "2002 BW"});
 bikes.put("2003", new String[] {"2003 S320"});
 bikes.put("2004", new String[] {"2004 TA1", "2004 TA2", "2004 TA3"});
 }

 public String[] getYears() {
 String[] keys = new String[bikes.size()];
 int i = 0;
 for(String key : bikes.keySet()) {
 keys[i++] = key;
 }
 return keys;
 }

 public String[] getBikes(String year) {
 return bikes.get(year);
 }
}

getYears()跟getBkies()分別表示產品的年份跟型號，這邊用Map模擬，實際上資料是來自資料庫的查詢。

一樣的，在dwr.xml中設定：
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 1.0//EN" "http://www.getahead.ltd.uk/dwr/dwr10.dtd">

<dwr>
 <allow>
 <create creator="new" javascript="Bike" scope="application">
 <param name="class" value="onlyfun.caterpillar.Bike"/>
 </create>
 </allow>
</dwr>

我們會有個腳踏車年份與型號查詢頁面：
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=BIG5">
<title>Insert title here</title>
 <script type='text/javascript' src='dwr/interface/Bike.js'></script>
 <script type='text/javascript' src='dwr/engine.js'></script>
 <script type='text/javascript' src='dwr/util.js'></script>
 <script type='text/javascript' src='bike.js'></script>
</head>
<body onload="refreshYearList();">
 年份：<select id="years" onchange="refreshBikeList();"></select> 
 型號：<select id="bikes"></select> 
</body>
</html>

注意，在選完第一個年份後，會觸發onchange事件，接著第二個下拉選單會自動填上對應年份的型號，而不是按鈕按下，再去取得第二個下拉選單，然後refresh...blah...blah...

bike.js如下…
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function refreshYearList() {
 Bike.getYears(populateYearList);
}

function populateYearList(list){
 DWRUtil.removeAllOptions("years");
 DWRUtil.addOptions("years", list);
 refreshBikeList();
}

function refreshBikeList() {
 var year = $("years").value;
 Bike.getBikes(year, populateBikeList);
}

function populateBikeList(list){
 DWRUtil.removeAllOptions("bikes");
 DWRUtil.addOptions("bikes", list);
}

一樣很簡單…

看個無聊的畫面…XD