JSON(JavaScript Object Notation,JS 对象标记)是一种轻量级的数据交换格式
采用完全独立于编程语言的文本格式来存储和表示数据
JSON 键值对是用来保存 JavaScript 对象的一种方式
比如:{"name": "张三"},前者键,后者值,冒号分隔
写个 HTML
script 写在 <head> 里
html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<script type="text/javascript">
var user = {
name:"张三",
age:18,
sex:"男"
};
console.log(user);
</script>
</head>
<body>
</body>
</html>
直接在 idea 里查看网页效果
可以看到控制台打印成功
js 和 json 可以互相转换
html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<script type="text/javascript">
var user = {
name:"张三",
age:18,
sex:"男"
};
//将 js 对象转换成 json 对象
var json = JSON.stringify(user);
console.log(json);
//将 json 对象转换成 js 对象
var obj = JSON.parse(json);
console.log(obj);
</script>
</head>
<body>
</body>
</html>
前者字符串,后者对象
Jackson 是 json 解析工具
pom.xml 文件导入 jackson 的 jar 包
XML
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.17.2</version>
</dependency>
配置 web.xml 文件:
XML
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0"
metadata-complete="true">
<!-- 注册servlet -->
<servlet>
<servlet-name>springmvc</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<!-- 通过初始化参数指定SpringMVC配置文件的位置进行关联 -->
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:springmvc-servlet.xml</param-value>
</init-param>
<!-- 启动顺序 -->
<load-on-startup>1</load-on-startup>
</servlet>
<!-- 所有请求都会被SpringMVC拦截 -->
<servlet-mapping>
<servlet-name>springmvc</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
<!-- 配置SpringMVC的乱码过滤 -->
<filter>
<filter-name>encoding</filter-name>
<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>utf-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encoding</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>
resources 目录下创建 springmvc-servlet.xml 文件
XML
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.2.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">
<!-- 自动扫描包,让指定包下的注解生效,由IOC容器统一管理 -->
<context:component-scan base-package="com.demo.controller"/>
<!-- 让SpringMVC不处理静态资源 -->
<mvc:default-servlet-handler/>
<!-- 支持MVC注解驱动 -->
<mvc:annotation-driven/>
<!-- 视图解析器 -->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"
id="InternalResourceViewResolver">
<!-- 前缀 -->
<property name="prefix" value="/WEB-INF/jsp/"/>
<!-- 后缀 -->
<property name="suffix" value=".jsp"/>
</bean>
</beans>
pom.xml 文件导入 lombok 的 jar 包
XML
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.34</version>
<scope>provided</scope>
</dependency>
写个 User 类,设置有参构造和无参构造的注解
java
package com.demo.pojo;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
//需要导入lombox
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
private String name;
private int age;
private String sex;
}
写个控制器
@ResponseBody 表示不走视图解析器,直接返回字符串
jackson 使用方法:
-
new 一个 ObjectMapper
-
调用 writeValueAsString 方法,转换成 String 类型
方法1:可以使用 @RequestMapping 注解里的 produces 解决 json 乱码
produces = "application/json;charset=utf-8"
java
package com.demo.controller;
import com.demo.pojo.User;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
public class UserController {
//解决中文乱码
@RequestMapping(value = "/json",produces = "application/json;charset=utf-8")
//@RequestMapping("/json")
@ResponseBody //加了@ResponseBody表示不走视图解析器,返回字符串
public String json() throws JsonProcessingException {
//jackson
ObjectMapper mapper = new ObjectMapper();
//创建一个对象
User user = new User("张三",18,"男");
String value = mapper.writeValueAsString(user);
//return user.toString();
return value;
}
}
json 请求时出现乱码,SpringMVC 提供了统一解决乱码的方式
方法2:springmvc-servlet.xml 文件添加 json 解决乱码配置
XML
<!-- JSON乱码问题配置 -->
<mvc:annotation-driven>
<mvc:message-converters register-defaults="true">
<bean class="org.springframework.http.converter.StringHttpMessageConverter">
<constructor-arg value="UTF-8"/>
</bean>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper">
<bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
<property name="failOnEmptyBeans" value="false"/>
</bean>
</property>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
这段配置固定,写了 json 就把这段加上
运行,中文可以正常显示
如果设置了 @RestController 注解,表示只返回 json 形式
java
package com.demo.controller;
import com.demo.pojo.User;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.ArrayList;
import java.util.List;
@RestController
public class UserController {
@RequestMapping("/json2")
public String json2() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
List<User> userList = new ArrayList<User>();
User user1 = new User("张三1",18,"男");
User user2 = new User("张三2",18,"男");
User user3 = new User("张三3",18,"男");
userList.add(user1);
userList.add(user2);
userList.add(user3);
String value = mapper.writeValueAsString(userList);
return value;
}
}
中括号表示这是一个 list 集合
大括号表示它是一个具体的对象
获取时间:
java
package com.demo.controller;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.text.SimpleDateFormat;
import java.util.Date;
@RestController
public class UserController {
@RequestMapping("/json3")
public String json3() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
Date date = new Date();
//自定义日期格式
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//ObjectMapper,时间解析后的默认格式为:Timestamp时间戳
return mapper.writeValueAsString(simpleDateFormat.format(date));
}
}
FastJson可以实现 json 对象与 JavaBean 对象的转换
实现 JavaBean 对象与 json 字符串的转换
实现 json 对象与 json 字符串的转换
导入 fastjson 的 jar 包
XML
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>2.0.51</version>
</dependency>
直接使用 JSON.toJSONString 即可
java
package com.demo.controller;
import com.alibaba.fastjson.JSON;
import com.demo.pojo.User;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.ArrayList;
import java.util.List;
@RestController
public class UserController {
@RequestMapping("/json4")
public String json4() throws JsonProcessingException {
List<User> userList = new ArrayList<User>();
User user1 = new User("张三1",18,"男");
User user2 = new User("张三2",18,"男");
User user3 = new User("张三3",18,"男");
userList.add(user1);
userList.add(user2);
userList.add(user3);
String value = JSON.toJSONString(userList);
return value;
}
}
Java 对象转 JSON 字符串:JSON.toJSONString()
JSON 字符串转 Java 对象:JSON.parseObject()
Java 对象转 JSON 对象:JSON.toJSON()
JSON 对象转 Java 对象:JSON.toJavaObject()