ajax可以发送post或者get请求，并且可以设置同步或者异步，这里罗列了几种。其中，后台处理请求由servlet实现。

第一种方式：

var xmlhttp = new XMLHttpRequest();
//发送post请求，false表示发送同步请求
xmlhttp.open("POST","AdminLogin",false);
//设置文件的头,UTF-8应与html编码格式一致，告诉浏览器对参数编码的格式，可以解决中文传输乱码的问题
xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded;charset=UTF-8");
//设置传递的参数
xmlhttp.send("id="+id+"&password="+password);
//显示返回结果
alert(xmlhttp.responseText);

第二种方式（接受JSON包）：

//使用ajax方法,JS代码
$.ajax({
    url: "GetStudentInfo",type: 'POST',async: false,contentType: 'application/json',mimeType: 'application/json',success: function (data) {//对返回值的处理
		$("#id").val(data.id);
		$("#name").val(data.name);
		$("#year").val(data.year);
		$("#specialty").val(data.specialty);
		$("#phone").val(data.phone);
		$("#email").val(data.email);
    },});

//Servlet代码
public class User {
	public String id;
	public String name;
	public String year;
	public String specialty;
	public String phone;
	public String email;
}

protected void doPost(HttpServletRequest request,HttpServletResponse response)
    throws ServletException,IOException {
	ObjectMapper mapper = new ObjectMapper();
        Connection con = DBTool.getConnection();
	User u = new User();
	u.id = "a";
	u.name = "b";
	u.year = "c";
	u.specialty = "d";
	u.phone = "e";
	u.email = "f";
	response.setContentType("application/json");  
}

//JS代码
$.ajax({
      url: "CheckAllStudent",success: function (data) {
          $.each(data,function (index,student) {
        	var string = "<tr>";
        	string += "<td>" + student.id+ "</td>";
        	string += "<td>" + student.name+ "</td>";
        	string += "<td>" + student.year+ "</td>";
        	string += "<td>" + student.specialty+ "</td>";
        	string += "<td>" + student.phone+ "</td>";
        	string += "<td>" + student.email+ "</td>";
        	$("tbody").append(string);
          }); 
      },});

//Servlet代码
protected void doPost(HttpServletRequest request,HttpServletResponse response) 
    throws ServletException,IOException {
    	ObjectMapper mapper = new ObjectMapper();
    	//把相同的对象放入List中
    	List<User>	list = new ArrayList<User>();
    	User u1,u3;
    	list.add(u1);
    	list.add(u2);
    	list.add(u3);
	response.setContentType("application/json");  
	mapper.writeValue(response.getOutputStream(),list);
}

第四种方式（ajax方法，带参数）：

$.ajax({
	url: "ShowAdvertise",data: {time:time},success: function(data) {
		alert(data);
	},});

jQuery ajax - ajax() 方法