DWR 入門與應用（三）

來寫個AJAX版的聊天室吧！先看看直接使用AJAX要如何做到，首先需要一個簡單的聊天室Servlet…

 onlyfun.caterpillar;

 java.io.IOException;
 java.io.PrintWriter;
 java.util.LinkedList;
 java.util.List;

 javax.servlet.ServletException;
 javax.servlet.http.HttpServletRequest;
 javax.servlet.http.HttpServletResponse;

  ChatRoomServlet  javax.servlet.http.HttpServlet  javax.servlet.Servlet 
  LinkedList<Message> messages =  LinkedList<Message>();

 ChatRoomServlet() 
(); 


 List<Message> addMessage(String text) 
 (text !=  && text.trim().length() > 0) 
            messages.addFirst( Message(text));
 (messages.size() > 10) 
                messages.removeLast();



 messages;


 List<Message> getMessages() 
 messages;


  doPost(HttpServletRequest request, HttpServletResponse response)  ServletException, IOException 
        List<Message> list = ;

(.equals(request.getParameter())) 
             list = addMessage(request.getParameter());

 (.equals(request.getParameter()))
             list = getMessages();


        PrintWriter out = response.getWriter();
        response.setContentType();
        response.setHeader(, );

        out.println();
( i = 0; i < list.size(); i++) 
            String msg = list.get(i).getText();
            out.println( + msg + );

        out.println();

Message物件如下…

 onlyfun.caterpillar;

  Message 
  id = System.currentTimeMillis();
 String text;

 Message(String newtext) 
        text = newtext;
 (text.length() > 256) 
            text = text.substring(0, 256);

        text = text.replace(, );
        text = text.replace(, );


  getId() 
 id;


 String getText() 
 text;

Servlet接受訊息新增與查詢，判斷的方式是檢查請求參數task是send或query。

Servlet會以XML傳回目前List當中的訊息，客戶端可以查詢或插入新訊息時，取得目前List中的訊息，接著在web.xml中設定一下…

<?xml version= encoding=?>
<web-app id= version= xmlns= xmlns:xsi= xsi:schemaLocation=>
  <servlet>
    <description>
    </description>
    <display-name>
    ChatRoomServlet</display-name>
    <servlet-name>ChatRoomServlet</servlet-name>
    <servlet-class>
    onlyfun.caterpillar.ChatRoomServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>ChatRoomServlet</servlet-name>
    <url-pattern>/ChatRoomServlet</url-pattern>
  </servlet-mapping>
  <session-config>
    <session-timeout>
            30
        </session-timeout>
  </session-config>  
</web-app>

在網頁中，使用者可以在輸入訊息後按下按鈕送出資訊，並在XML回應取得時，將訊息以一列一列的表格方式顯示出來，另外還設定了週期性的輪詢，即使不輸入新訊息，也可以週期性的取得新的聊天訊息…

<!DOCTYPE HTML PUBLIC >
<html>
<head>
<meta http-equiv= content=>
<title>Chat Room</title>

<script type=>
var xmlHttp;

function createXMLHttpRequest() 
 (window.ActiveXObject) 
        xmlHttp =  ActiveXObject();

  (window.XMLHttpRequest) 
        xmlHttp =  XMLHttpRequest();



function sendMessage() 
  var msg = document.getElementById().value;

(msg == ) 
    refreshMessage();
;


  var param =  + msg;
  ajaxRequest(param);
  document.getElementById().value = ;


function queryMessage() 
  var param = ;
  ajaxRequest(param);


function ajaxRequest(param) 
  var url =  +  Date().getTime();
    createXMLHttpRequest();
  xmlHttp.onreadystatechange = refreshMessage;
    xmlHttp.open(, url, );
  xmlHttp.setRequestHeader(,
);
    xmlHttp.send(param);


function refreshMessage() 
(xmlHttp.readyState == 4) 
(xmlHttp.status == 200) 
          var messages = xmlHttp.responseXML.getElementsByTagName();

          var table_body = document.getElementById();
      var length = table_body.childNodes.length;
 (var i = 0; i < length; i++) 
        table_body.removeChild(table_body.childNodes[0]);


      var length = messages.length;
(var i = length - 1; i >= 0 ; i--) 
              var message = messages[i].firstChild.data;
              var row = createRow(message);

              table_body.appendChild(row);                        

      setTimeout(, 2000);




function createRow(message) 
    var row = document.createElement();
    var cell = document.createElement();
    var cell_data = document.createTextNode(message);
    cell.appendChild(cell_data);
    row.appendChild(cell);
 row;


</script>

</head>
<body>

<p>
  Your Message:
  <input id=/>
  <input type= value=
      onclick=/>
</p>

<p>Messages:</p>
    <table align=>
        <tbody id=></tbody>
    </table>

</body>
</html>

簡單抓個畫面…

直接用AJAX，後端用JSP/Servlet，您要對請求參數做些判斷，看看是新增訊息或查詢，並要自行輸出XML，有的沒的…

改成DWR的話，就很簡單了，寫個簡單的Java物件…

 onlyfun.caterpillar;

 java.util.LinkedList;
 java.util.List;

  Chat 
  LinkedList<Message> messages =  LinkedList<Message>();

 List addMessage(String text) 
 (text !=  && text.trim().length() > 0) 
      messages.addFirst( Message(text));
 (messages.size() > 10) 
        messages.removeLast();



 messages;


 List getMessages() 
 messages;

接著…在dwr.xml中開放一下…

<?xml version= encoding=?>
<!DOCTYPE dwr PUBLIC  >

<dwr>
  <allow>

    <create creator= javascript=>
      <param name= value=/>
    </create>

    <convert converter= match=/>      
  </allow>
</dwr>

使用者取得訊息時，是直接傳回List物件，而List中裝的是Message物件，Message物件是自訂物件，conterver設定為 bean，表示DWR會自動將Message的getter名稱轉換為傳回客戶端的JavaScript物件中的屬性，例如Message中有 getText()，則在客戶端可以用message.text這樣的方式來存取。

接著是簡單的客戶端網頁…

<!DOCTYPE HTML PUBLIC >
<html>
<head>
<meta http-equiv= content=>
<title>Insert title here</title>

<script src= type=></script>
<script src= type=></script>
<script src= type=></script>

<script type=>
function sendMessage() 
    var text = DWRUtil.getValue();
    DWRUtil.setValue(, );
    Chat.addMessage(text, gotMessages);


function gotMessages(messages) 
    var chatlog = ;
 (var data in messages) 
        chatlog =  + messages[data].text +
 + chatlog;

    DWRUtil.setValue(, chatlog);
  setTimeout(, 2000);


function queryMessage() 
  Chat.getMessages(gotMessages);

</script>

</head>
<body>

<p>
  Your Message:
  <input id=/>
  <input type= value=
      onclick=/>
</p>

<p>Messages:</p>
<div id=></div>

</body>
</html>

當List物件傳回時，它成為gotMessages(messages)中的messages物件，而messages物件中包括 Message物件轉換後對應的JavaScript物件，由於我們已經設定了Converter，所以可以用messages[data].text來取得傳回的訊息…

簡單抓個畫面…
DWR 入門與應用（三）