【正文】 st調(diào)用已經(jīng)完成、 HTTP狀態(tài)碼為 200、表示 HTTP交互已經(jīng)成功 ?？梢允褂?XML文檔的字符串表示、如下所示： message valid /message 上面的例子是一個簡單的 XML片段、實際應(yīng)用可能包含更多： function parseMessage() { var message = (message)[0]。 JavaScript可以獲得 HTML DOM中任何元素（對象）的引用、推薦使用(userIdMessage)方法來獲取。 } /script body div id=userIdMessage/div /body innerHTML屬性被改變以后網(wǎng)頁可以立即體現(xiàn)出變化、如果 innerHTML屬性內(nèi)部包含象 image、 iframe這樣的元素、那么其所指定的資源內(nèi)容一樣被瀏覽器解析顯示。 var messageElement = (message)。 (color, red)。 支持的 JavaScript的 DOM API的技術(shù)可以在各種不同的瀏覽器，所以你必須照顧 到正在發(fā)展中的應(yīng)用軟件。 標(biāo)準(zhǔn)化 XMLHttpRequest對象： XMLHttpRequest對象是尚未加入的 JavaScript技術(shù)規(guī)范，這意味著行為可能會有所變化，這取決于客戶端。 調(diào)試： Ajax應(yīng)用也很難調(diào)試，因為處理邏輯是嵌入在客戶端和服務(wù)器上。 不善的設(shè)計基于 Ajax的應(yīng)用程序可以打開自己黑客的攻擊或剽竊。 Java技術(shù)提供了一個良好的基礎(chǔ)，以開發(fā)和部署基于 Ajax的應(yīng)用程序的 API的滯留在 HTTP處理，數(shù)據(jù)庫， Web服務(wù)， XML處理，和 Business Objects 。 作為應(yīng)用架構(gòu)師或開發(fā)人員，您將要權(quán)衡 這樣的 需要 具有豐富的應(yīng)用程序?qū)g覽器的支持，結(jié)構(gòu)復(fù)雜，技術(shù)和開發(fā)培訓(xùn)。s XMLHttpRequest object. Although this object is not specified in the formal JavaScript technology specification, all of today39。s put all the pieces together and look at an Ajaxenabled Java application. Let39。 function validate() { var idField = (userid)。 } (GET, url, true)。 the URL of the serverside ponent that the object will interact with。 (id= + encodeURIComponent())。 = ()。 if ((targetId != null) amp。 ().write(messagevalid/message)。 } } } In this example, a simple HashMap is used to contain the users. In the case of this example, let us assume that the user typed duke as the ID. 5. The ValidateServlet returns an XML document containing the results. The user ID duke is present in the list of user IDs in the users HashMap. The ValidateServlet will write an XML document to the response containing a message element with the value of invalid. More plex usecases may require DOM, XSLT, or other APIs to generate the response. (text/xml)。s look at how to use the DOM APIs in JavaScript technology by looking at the following XML document returned from the ValidateServlet. message valid /message This example is a simple XML fragment that contains the sender of the message element, which is simply the string valid or invalid. A more advanced sample may contain more than one message and valid names that might be presented to the user: function parseMessage() { var message = (message)[0]。 modify the element39。 } else { = div style=\color:green\Valid User Id/ div。 messageText = Invalid User Id。 // if the messageBody element has been created simple replace it otherwise // append the new element if ([0]) { (messageBody, [0])。s applications can bee more interactive, providing the end user with a better experience. Using Ajax requires that you use the latest browser versions that support the XMLHttpRequest object needed for Ajax interactions. Using Ajax also requires a great deal of clientside JavaScript technology and CSS. As an application architect or developer, you will need to weigh the needs of having a rich application against browser support, architecture plexity, and developer training. As the Ajax programming model evolves, existing technologies and frameworks will make this transition easier. What is evident is that prominent web applications are increasingly being more interactive. Are yours? 。 } } /script body div id=userIdMessage/div /body The code sample shows how JavaScript technology DOM APIs may be used to create an element or alter the element programmatically. The support for JavaScript technology DOM APIs can differ in various browsers, so you must take care when developing applications. Final Thoughts Although many of these benefits are noteworthy, this approach has some challenges as well: Complexity: Serverside developers will need to understand that presentation logic will be required in the HTML client pages as well as in the serverside logic to generate the XML content needed by the client HTML pages. HTML page developers need to have a basic understanding of JavaScript technology to create new Ajax functionality. Other options such as Project jMaki and Project Dynamic Faces provide a way for Java developers to better use Ajax functionality without requiring deep knowledge of JavaScript technology. Standardization of the XMLHttpRequest object: The XMLHttpRequest object is not yet part of the JavaScript technology specification, which means that the behavior may vary depending on the client. It39。 messageText = Valid User Id。 var messageText。 or add, remove, or modify child elements. One mon means to change the body content of an element is to set the innerHTML property on the element as in the following example. script type=text/javascript ... function setMessage(message) { var mdiv = (userIdMessage)。 } The parseMessages() function will process an XML document retrieved from the ValidateServlet. This function will call the setMessage() with the value of the message element to update the HTML DOM. 7. The HTML DOM is updated. JavaScript technology can gain a reference to any element in the HTML DOM using a number of APIs. The remended way to gain a reference to an element is to call (userIdMessage), where userIdMessage is the ID attribute of an element appearing in the HTML document. With a reference to the element, JavaScript technology may now be used to modify the element39。 ().write(invalid)。 (CacheControl, nocache)。 !(())) { (text/xml)。 (duke,account data)。 private HashMap users = new HashMap()。. See section 6 for more details. 3. The XMLHttpRequest object makes a call. When the statement (null)。 (null)。 if (typeof XMLHttpRequest != undefined) { re