Ajax与服务器通信：发送请求和处理响应(2/4)

要想充分发挥ajax的强大功能，这要求你向服务器发送一些上下文数据。

XMLHttpRequest对象的工作与以往惯用的HTTP技术（GET和POST）是一样的。

在下面的例子中，主要介绍这两种请求方式。
其中GET请求，我们向应用程序发送了3个参数：firstName,middleName,birthday.
其中资源URL和参数之间要用一个问号(?),问号后面就是名/值对。其采用name=value的形式，各个名值对之间用与（&）号分隔。
如：http://localhost:8080/yourapp/servlet/GetAndPostExample?firstName=Harry&middleName=Poter&birthday=20101010

服务器知道如何获取URL中的命名参数。

采用POST方法向服务器发送命名参数时，与采用GET时类似。POST方法也会将参数编码为名/值对。
这两种方式的主要区别在于，POST方法将参数串放在请求体中发送，而GET方法是将参数追加到URL中发送。

该示例有两个文件，其一为getandpost.html,另一个为servlet GetAndPostExample.java

详细代码如下：

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>getAndPost.html</title>
<Meta http-equiv="content-type" content="text/html; charset=UTF-8">
<script language="javascript" type="text/javascript">
var xmlHttp;
function createXMLHttpRequest(){
if(window.ActiveXObject)
{
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
else if(window.XMLHttpRequest)
{
xmlHttp = new XMLHttpRequest();
}else{
alert("浏览器不支持XMLHttpRequest对象");
}
}
function createQueryString(){
var firstName = document.getElementById("firstName").value;//document.getElementById("firstName").value;
//alter(document.getElementById("firstName").value);
var middleName = document.getElementById("middleName").value;
var birthday = document.getElementById("birthday").value;
//var birthday = document.getElementByID("birthday").value; //这句是错的！！！因为ID的d要小写！！！！！
var queryString = "firstName="+ firstName + "&middleName="+ middleName + "&birthday=" + birthday;
//alert(queryString);
return queryString;
}
function doRequestUsingPOST(){
createXMLHttpRequest();
var url = "servlet/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);
}
function doRequestUsingGET(){
createXMLHttpRequest();
var queryString = "servlet/GetAndPostExample?";
//alert(createQueryString());
queryString = queryString + createQueryString() + "&timeStamp=" + new Date().getTime();
alert("oo");
xmlHttp.onreadystatechange = handleStateChange;
xmlHttp.open("GET",queryString,true);
xmlHttp.send(null);
}
function handleStateChange(){
if(xmlHttp.readyState == 4){
if(xmlHttp.status == 200){
parseResult();
alert("OK");
}
}
}
function parseResult(){
var responseDiv = document.getElementById("serverResponse");
if(responseDiv.hasChildNodes()){
responseDiv.removeChild(responseDiv.childNodes[0]);
}
var responseText = document.createTextNode(xmlHttp.responseText);
responseDiv.appendChild(responseText);
}
function test(){
alert(document.getElementById("firstName").value);
}
</script>
</head>
<body>
<h2>
Enter your first name, middle name ,and birthday:
</h2>
<form action="#" id="form1" name="form1" >
<table>
<tbody>
<tr>
<td>
First Name:
</td>
<td>
<input type="text" id="firstName" value="Harry" />
</td>
</tr>
<tr>
<td>
Middle Name:
</td>
<td>
<input type="text" id="middleName" value="Poter" />
</td>
</tr>
<tr>
<td>
Birthday:
</td>
<td>
<input type="text" id="birthday" value="2020-8-9" />
</td>
</tr>
</tbody>
</table>
<input type="button" value="Send parameters using GET"
onclick="doRequestUsingGET();" />
<input type="button" value="Send parameters using POST"
onclick="doRequestUsingPOST()" />
<input type="button" value="Test"
onclick="return test()" />
</form>
<br />
<h2>
Server Response:
</h2>
<div id="serverResponse">
这里将会显示来自服务器端的相应信息
</div>
</body>
</html>

package ajax.study;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
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 brower
PrintWriter out = response.getWriter();
out.println(responseText);
//close the writer
out.close();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//process the request in method processRequest
processRequest(request,response,"GET");
}
public void doPost(HttpServletRequest request,"POST");
}
}

原文链接：https://www.f2er.com/ajax/166286.html

Ajax与服务器通信：发送请求和处理响应(2/4)

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