Ajax——json

json是js提供的一种数据交换格式！

json的语法
* {}：是对象！
> 属性名必须使用双引号括起来！单引不行！！！
> 属性值：
* null
* 数值
* 字符串
* 数组：使用[]括起来
* boolean值：true和false

应用json

var person = {"name":"zhangSan","age":18,"sex":"male"};

json与xml比较
* 可读性：XML胜出
* 解析难度：JSON本身就是JS对象（主场作战），所以简单很多
* 流行度：XML已经流行好多年，但在AJAX领域，JSON更受欢迎。

package servlet;

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;

import org.junit.Test;

public class AServlet extends HttpServlet {

	
	public void doGet(HttpServletRequest request,HttpServletResponse response)
			throws ServletException,IOException {

		response.setContentType("text/html;charset=utf-8");
		String str="{\"name\":\"Zhangsan\",\"age\":16,\"sex\":\"male\"}";
		response.getWriter().print(str);
		System.out.println(str);
	}
	

}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'json1.jsp' starting page</title>
    
	<Meta http-equiv="pragma" content="no-cache">
	<Meta http-equiv="cache-control" content="no-cache">
	<Meta http-equiv="expires" content="0">    
	<Meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<Meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
<script type="text/javascript">
function createXMLHttpRequest(){
	try {
		return new XMLHttpRequest();
	} catch (e) {
		try {
			return new ActiveXObject("Msxml2.XMLHTTP");
		} catch (e) {
			try {
				return new ActiveXObject("MicroSoft.XMLHTTP");
			} catch (e) {
				// TODO: handle exception
			}
		}
	}
}
window.onload=function(){
	var bt=document.getElementById("bt");
	bt.onclick=function(){
		var xmlHttp=createXMLHttpRequest();
		xmlHttp.open("GET","<c:url value='/AServlet' />",true);
		xmlHttp.send(null);
		xmlHttp.onreadystatechange=function(){
			if(xmlHttp.readyState==4 && xmlHttp.status==200){
				var text=xmlHttp.responseText;
				var person=eval("("+text+")");
				var s=person.name+","+person.age+","+person.sex;
				document.getElementById("h1").innerHTML=s;
			}
		};
	};
};
</script>
  </head>
  
  <body>
    <h1>json演示</h1>
    <button id="bt">点击这里</button> 
    <h1 id="h1"></h1>
  </body>
</html>

json-lib可以把javabean转换成json串

核心类
* JSONObject --> Map
> toString();
> JSONObject map = JSONObject.fromObject(person)：把对象转换成JSONObject对象
* JSONArray --> List
> toString()
> JSONArray jsonArray = JSONObject.fromObject(list)：把list转换成JSONArray对象

package demo;

import java.util.ArrayList;
import java.util.List;

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

import org.junit.Test;

public class Demo {
	@Test
	public void fun1(){
		JSONObject map=new JSONObject();
		map.put("name","ZHangsan");
		map.put("age",16);
		map.put("sex","male");
		String s = map.toString();
		System.out.println(s);
		
	}
	@Test
	public void fun2() {
		Person p=new Person("Lisi",18,"male");
		//把对象转换成JSONObject对象
		JSONObject map=JSONObject.fromObject(p);
		String s = map.toString();
		System.out.println(s);
	}
	@Test
	public void fun3() {
		Person p1=new Person("Lisi",55,"male");
		Person p2=new Person("haha",33,"male");

		JSONArray list=new JSONArray();
		list.add(p1);
		list.add(p2);
		String s = list.toString();
		System.out.println(s);
	}
	
	@Test
	public void fun4() {
		Person p1=new Person("Lisi","male");
		List<Person> list=new ArrayList<Person>();
		list.add(p1);
		list.add(p2);
		
		System.out.println(JSONArray.fromObject(list));
	}

}

Ajax——json

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