首先看下看下相对简单些的--向服务器发送一个包含有名/值对的简单查询串，在这种情况下XHP即可以用GET也可以用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/值对的参数形式了（如name=LiLin&age=23）,在调用OPEN方法中，当请求方法是用POST的时候为了确保服务器知道请求体中有请求参数，需要调用setRequestHeader，将Content-Type值设置为application/x -www-form-urlencoded.当然也可不放在请求体中（那就不要用POST啦！）

　　此时server处理：

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来处理。

　　要向服务器发送相关复杂的查询串，可以将模型变化为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 " ,