AJAX编程实际之与服务器通讯

AJAX编程实际之与服务器通讯

　　首先看下看下相对简略些的--向服务器发送一个蕴含有名/值对的简略查询串，在这种情况下XHP即可能用GET也可能用POST。

GET

function doRequestUsingGET() {
　createXMLHttpRequest();

　var queryString = " GetAndPostExample? " ;
　queryString = queryString + createQueryString()+ " &timeStamp= " + new Date().getTime();
　xmlHttp.onreadystatechange = handleStateChange;
　xmlHttp.open( " GET " , queryString, true );
　xmlHttp.send( null );
}

POST

function doRequestUsingPOST() {
　createXMLHttpRequest();

　var url = " GetAndPostExample?timeStamp= " + new Date().getTime();
　var queryString = createQueryString();

　xmlHttp.open( " POST " , url, true );
　xmlHttp.onreadystatechange = handleStateChange;
　xmlHttp.setRequestHeader( " Content-Type " , " application/x-www-form-urlencoded " );
　xmlHttp.send(queryString);
}

　　queryString就是名/值对的参数方式了（如name=LiLin&age=23）,在调用OPEN方法中，当申请方法是用POST的时分为了确保服务器知道申请体中有申请参数，需求调用setRequestHeader，将Content-Type值设置为application/x-www-form-urlencoded.当然也可不放在申请体中（那就不要用POST啦！）

　　此时server解决：

import java.io. * ;
import java.net. * ;
import javax.servlet. * ;
import javax.servlet.http. * ;

public class GetAndPostExample extends HttpServlet {

　protected void processRequest(HttpServletRequest request, HttpServletResponse response, String method)
throws ServletException, IOException {

　　// Set content type of the response to text/xml
　　response.setContentType( " text/xml " );

　　// Get the user's input
　　String firstName = request.getParameter( " firstName " );
　　String middleName = request.getParameter( " middleName " );
　　String birthday = request.getParameter( " birthday " );

　　// Create the response text
　　String responseText = " Hello " + firstName + " " + middleName
+ " . Your birthday is " + birthday + " . "
+ " [Method: " + method + " ] " ;

　　// Write the response back to the browser
　　PrintWriter out = response.getWriter();
　　out.println(responseText);

　　// Close the writer
　　out.close();
　}

　protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
　　// Process the request in method processRequest
　　processRequest(request, response, " GET " );
　}

　protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
　　// Process the request in method processRequest
　　processRequest(request, response, " POST " );
　}
}

　　对get and post方法都用processRequest来解决。

　　要向服务器发送相干简单的查询串，可能将模型变化为XML发送到server 。

　　client端:

function createXML() {
　var xml = " <pets> " ;

　var options = document.getElementById( " petTypes " ).childNodes;
　var option = null ;
　for ( var i = 0 ; i < options.length; i ++ ) {
　　option = options[i];
　　if (option.selected) {
　　　xml = xml + " <type> " + option.value + " <\/type> " ;
　　}
　}

　xml = xml + " <\/pets> " ;
　return xml;
}

function sendPetTypes() {
　createXMLHttpRequest();

　var xml = createXML();
　var url = " PostingXMLExample?timeStamp= " + new Date().getTime();

　xmlHttp.open( " POST " , url, true );
　xmlHttp.onreadystatechange = handleStateChange;
　xmlHttp.setRequestHeader( " Content-Type " , " application/x-www-form-urlencoded " );
　xmlHttp.send(xml);
}

　　createXML方法无非就是将内容以DOM的样式存到var xml（变量）里。有时也能够出现client间接将本地的一个XML文件间接以DOM（当然可能edit）的样式传送.(也放这个时个的Content-Type应该为text/xml了!)这时能够要用到ActiveXObject("MSXML2.DOMDocument.3.0")这样一个控件了。

　　关于这个控件有个方法可能在各broswer中通用的JS代码：

// --------------------------------------------------------------------
// Function: CreateXMLDOM
//
// Purpose: Creates a new XML DOM.
//
// Parameters: None
//
// Returns: XMLDOM object OR null
// --------------------------------------------------------------------
function CreateXmlDOM()
{
　var oXML = new ActiveXObject(GetXmlParserProgID());
　try
　{
　　oXML.setProperty( " AllowXsltScript " , true );
　}
　catch (err) {}