什么是JSON
json的全英文名字是JavaScript Object Notation ,它是一种JavaScript对象标识法。
一般而言java中表示常见的对象表示方法有:
Person p = new Person();
p.setName("张三");
p.setAge(23);
p.setGender("男");
var p = {
"name":"李四","age":23,"gender":"女"};
若用js对象表示
var p = {
"name":"李四","age":23,"gender":"女"};
json其实就是js对象表示中的一种。json现在多用于存储和交换文本信息的语法进行数据的传输JSON 比 XML 更小、更快,更易解析。
JSON如何使用
语法
总体规则
数据在名称/值对中:json数据是由键值对构成的
键用引号(单双都行)引起来,也可以不使用引号
值得取值类型:
- 数字(整数或浮点数)
- 字符串(在双引号中)
- 逻辑值(true 或 false)
- 数组(在方括号中) {“persons”:[{},{}]}
- 对象(在花括号中) {“address”:{“province”:“浙江”…}}
- null
数据由逗号分隔:多个键值对由逗号分隔
花括号保存对象:使用{}定义json 格式
方括号保存数组:[]
定义json的若干种方式:
window.onload=function () {
//基本格式
var person = {
"name":"zhangsan",age:23,"gender":true};
alert(person);
//嵌套格式 {}---->[]
var persons= {
"persons":[
{
"name":"zhangsan",age:23,"gender":true},
{
"name":"lisi",age:23,"gender":true},
{
"name":"wangwu",age:23,"gender":false}
]
};
alert(persons)
//嵌套格式 []----->{}
var ps=[
{
"name":"zhangsan",age:23,"gender":true},
{
"name":"lisi",age:23,"gender":true},
{
"name":"wangwu",age:23,"gender":false}
];
alert(ps);
}
JSON获取数据
获取单个json对象属性
var person = {
"name":"zhangsan",age:23,"gender":true};
let ps1=person.name;
var ps2 = person["name"];
alert(ps2);
alert(ps1);
获取json数组中对象的属性
方法一:
var persons= {
"persons":[
{
"name":"zhangsan",age:23,"gender":true},
{
"name":"lisi",age:23,"gender":true},
{
"name":"wangwu",age:23,"gender":false}
]
};
var name = persons.persons[2].name;
alert(name);
方法二:
var ps=[
{
"name":"wangwu",age:23,"gender":true},
{
"name":"lisi",age:23,"gender":true},
{
"name":"wangwu",age:23,"gender":false}
];
var ps1= ps[1].name;
alert(ps1);
JSON 遍历数据
遍历对象:
var person = {
"name":"zhangsan",age:23,"gender":true};
for(let key in person){
//这种获取方式有问题,相当于person.“key”
alert(key+":"+person[key]);
}
遍历对象数组
//嵌套格式 {}----->[]
var persons= {
"persons":[
{
"name":"zhangsan",age:23,"gender":true},
{
"name":"lisi",age:23,"gender":true},
{
"name":"wangwu",age:23,"gender":false}
]
};
var ps1 = persons.persons;
//alert(ps1);
for (let i = 0; i < ps1.length; i++) {
for(let key in ps1[i]){
//这种获取方式有问题,相当于person.“key”
alert(key+":"+ps1[i][key]);
}
}
//嵌套格式 []----->{}
var ps=[
{
"name":"zhangsan",age:23,"gender":true},
{
"name":"lisi",age:23,"gender":true},
{
"name":"wangwu",age:23,"gender":false}
];
for (let i = 0; i < ps.length; i++) {
let p = ps[i];
for(key in p){
alert(key+"-->"+p[key]);
}
}
JSON 和 JAVA对象的相互转换
JSON 解析器
常见的JSON解析器
JsonLib:JSON 官方提供
Gson: Google公司
fastJson: Alibaba
jackson:spring 中内置的一款Json解析器
由于jackson是与spring内置的json转换工具,下文重点说明jackson的相关方法。
JSON—>java
- 导入jackson的相关jar包
- 创建Jackson核心对象 ObjectMapper
- 调用ObjectMapper的相关方法进行转换
readValue(json字符串数据,Class)
java—>JSON
使用步骤:
- 导入jackson的相关jar包
- 创建Jackson核心对象 ObjectMapper
- 调用ObjectMapper的相关方法进行转换
```java
@Test
public void test05() throws Exception {
//1.初始化JSON字符串
String json = "{\"gender\":\"男\",\"name\":\"张三\",\"age\":23}";
//2.创建ObjectMapper对象
ObjectMapper mapper = new ObjectMapper();
//3.转换为Java对象 Person对象
Person person = mapper.readValue(json, Person.class);
System.out.println(person);
}
参数1:
File:将obj对象转换为JSON字符串,并保存到指定的文件中
Writer:将obj对象转换为JSON字符串,并将json数据填充到字符输出流中
OutputStream:将obj对象转换为JSON字符串,并将json数据填充到字节输出流中
writeValue(参数1,obj):
writeValueAsString(obj):将对象转为json字符串
2. 注解:
```java
1. @JsonIgnore:排除属性。
2. @JsonFormat:属性值得格式化
@JsonFormat(pattern = "yyyy-MM-dd")
- 复杂java对象转换
1)List:数组
2)Map:对象格式一致
校验用户名
服务器响应的数据,在客户端使用时,要想当做json数据格式使用。有两种解决方案:
- $.get(type):将最后一个参数type指定为"json"
- 在服务器端设置MIME类型
response.setContentType("application/json;charset=utf-8");
前端代码;
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>注册页面</title>
<script src="js/jquery-1.8.3.min.js"></script>
<script>
$(function () {
$("#username").blur(function () {
var username = $(this).val();
$.get("findUserServlet",{
username:username},function (data) {
let span = $("#s_username");
if(data.userExsit){
span.css("color","red");
span.html(data.msg);
}else {
span.css("color","green");
span.html(data.msg);
}
},"json");
});
})
</script>
</head>
<body>
<form>
<input type="text" id="username" name="username" placeholder="请输入用户名">
<span id="s_username"></span>
<br>
<input type="password" name="password" placeholder="请输入密码"><br>
<input type="submit" value="注册"><br>
</form>
</body>
</html>
后端代码;
@WebServlet("/findUserServlet")
public class FindUserServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String username = request.getParameter("username");
response.setContentType("text/html;charset=utf-8");
//response.setContentType("application/json;charset=utf-8");
Map<String, Object> map = new HashMap<>();
if("tom".equals(username)){
map.put("userExsit",true);
map.put("msg","此用户太受欢迎更换一个吧......");
}else{
map.put("userExsit",false);
map.put("msg","用户名可用");
}
ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(response.getWriter(),map);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
}
运行结果: