【正文】 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。 // if the messageBody element has been created simple replace it otherwise // append the new element if ([0]) { (messageBody, [0])。 messageText = Valid User Id。 messageText = Invalid User Id。 var messageText。 } else { = div style=\color:green\Valid User Id/ div。 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)。 modify the element39。 } 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。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]。 ().write(invalid)。 } } } 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)。 (CacheControl, nocache)。 ().write(messagevalid/message)。 !(())) { (text/xml)。 if ((targetId != null) amp。 (duke,account data)。 = ()。 private HashMap users = new HashMap()。 (id= + encodeURIComponent())。. See section 6 for more details. 3. The XMLHttpRequest object makes a call. When the statement (null)。 the URL of the serverside ponent that the object will interact with。 (null)。 } (GET, url, true)。 if (typeof XMLHttpRequest != undefined) { req = new XMLHttpRequest()。 function validate() { var idField = (userid)。s look at each step of the Ajax interaction in more detail. 1. A client event occurs. JavaScript technology functions are called as the result of an event. In this case, the function validate() may be mapped to a onkeyup event on a link or form ponent. input type=text size=20 id=userid name=id onkeyup=validate()。s put all the pieces together and look at an Ajaxenabled Java application. Let39。s or your service39。s XMLHttpRequest object. Although this object is not specified in the formal JavaScript technology specification, all of today39。 什么是顯而易見的 事 ，著名的 Web應(yīng)用正日益成為 并 更具互動(dòng)性。 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)。 使用 AJAX ，您需要使用最新的瀏覽器版本 它 支持 XMLHttpRequest對象需要 AJAX的 相互作用。 Java技術(shù)提供了一個(gè)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 。 見 限制進(jìn)入您的 Ajax服務(wù) 的更多信息，保護(hù)您的服務(wù)。 不善的設(shè)計(jì)基于 Ajax的應(yīng)用程序可以打開自己黑客的攻擊或剽竊。 框架，如 谷歌的Web工具包 已經(jīng)出現(xiàn)，使客戶端和服務(wù)器來回調(diào)試。 調(diào)試： Ajax應(yīng)用也很難調(diào)試，因?yàn)樘幚磉壿嬍乔度朐诳蛻舳撕头?wù)器上。 見 瀏覽器的差別。