AJAX編程實踐之與伺服器通訊

首先看下看下相對簡單些的--向伺服器發送一個包含有名/值對的簡單查詢串，在這種情況下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/值對的參數形式了（如name=LiLin&age=23）,在調用OPEN方法中，當要求方法是用POST的時候為了確保伺服器知道請求體中有請求參數，需要調用setRequestHeader，將Content-Type值設定為application/x-www-form-urlencoded.當然也可不放在請求體中（那就不要用POST啦！）

此時server處理：

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 " );
　}
}