100_JSON

目录

• 什么是JSON
• JSON和JavaScript对象互转
• Java使用JSON
  • 常用JSON工具
    • jackson
    • fastjson
  • 新建工程测试 jackson
    • 新建子模块，并添加web框架支持
    • pom.xml添加jackson依赖
    • Artifacts下WEB-INF中添加lib目录，添加jar，用于打包
    • 配置SpringMVC配置文件springmvc-servlet.xml
    • 配置web.xml
    • 编写实体类
    • 编写Controller，测试
      • 普通对象输出
      • 对象转json字符串输出
    • 统一处理乱码，springmvc-servlet.xml配置消息转换
      • 配置后，@GetMapping不配置produces = "application/json;charset=utf-8"，也不会乱码
    • 集合转json字符串输出
  • fastjson
    • fastjson三个主要的类
  • 测试 fastjson
    • pom.xml添加依赖
    • 测试
    • Java对象转json字符串
    • json字符串转Java对象
    • Java对象转json对象
    • json对象转Java对象

什么是JSON

JSON和JavaScript对象互转

Java使用JSON

常用JSON工具

jackson

fastjson

新建工程测试 jackson

新建子模块，并添加web框架支持

pom.xml添加jackson依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>spring-mvc</artifactId>
        <groupId>com.qing</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>springmvc-04-json</artifactId>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.12.4</version>
        </dependency>

    </dependencies>
</project>

Artifacts下WEB-INF中添加lib目录，添加jar，用于打包

配置SpringMVC配置文件springmvc-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        https://www.springframework.org/schema/mvc/spring-mvc.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.qing.controller"/>
    <!--让SpringMVC不处理静态资源，如：.css .js .html .mp3 .mp4-->
    <mvc:default-servlet-handler/>
    <!--
    支持MVC注解驱动
    在spring中一般采用@RequestMapping注解来完成映射关系
    要想使@RequestMapping注解生效，必须向上下文中注册DefaultAnnotationHandlerMapping和一个AnnotationMethodHandlerAdapter实例
    这两个实例分别在类和方法级别处理
    而annotation-driven配置帮助我们自动完成上述两个实例的注入
    -->
    <mvc:annotation-driven/>

    <!--视图解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver">
        <!--前缀和后缀-->
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
</beans>

配置web.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">

    <!--注册DispatcherServlet，这个是SpringMVC的核心：请求分发器，前置控制器-->
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!--DispatcherServlet要绑定SpringMVC的配置文件-->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-servlet.xml</param-value>
        </init-param>
        <!--启动级别设置为1-->
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <!--
        在SpringMVC中，/ 和 /*
        /：匹配所有的请求，不会匹配jsp页面
        /*：匹配所有的请求，包括jsp页面
        -->
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <!--编码过滤器-->
    <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>

编写实体类

package com.qing.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@NoArgsConstructor
@AllArgsConstructor
@Data
public class User {
    private String name;
    private String pwd;
    private int age;
}

编写Controller，测试

普通对象输出

package com.qing.controller;

import com.qing.pojo.User;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class UserController {

    @GetMapping(value = "/j1",produces = "application/json;charset=utf-8")
    @ResponseBody // 添加@ResponseBody，就不会走视图解析器
    public String json01() {
        User user = new User("张三丰","123456",999);
        return user.toString();
    }
}

对象转json字符串输出

package com.qing.controller;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.qing.pojo.User;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class UserController {

    @GetMapping(value = "/j2",produces = "application/json;charset=utf-8")
    @ResponseBody // 添加@ResponseBody，就不会走视图解析器
    public String json02() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        User user = new User("张三丰","123456",999);
        String jsonStr = mapper.writeValueAsString(user);
        return jsonStr;
    }
}

统一处理乱码，springmvc-servlet.xml配置消息转换

<!--
    支持MVC注解驱动
    在spring中一般采用@RequestMapping注解来完成映射关系
    要想使@RequestMapping注解生效，必须向上下文中注册DefaultAnnotationHandlerMapping和一个AnnotationMethodHandlerAdapter实例
    这两个实例分别在类和方法级别处理
    而annotation-driven配置帮助我们自动完成上述两个实例的注入
    -->
    <mvc:annotation-driven>
        <!--配置消息转换，解决乱码问题-->
        <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>

配置后，@GetMapping不配置produces = "application/json;charset=utf-8"，也不会乱码

package com.qing.controller;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.qing.pojo.User;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class UserController {

    @GetMapping("/j2")
    @ResponseBody // 添加@ResponseBody，就不会走视图解析器
    public String json02() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        User user = new User("张三丰","123456",999);
        String jsonStr = mapper.writeValueAsString(user);
        return jsonStr;
    }
}

集合转json字符串输出

package com.qing.controller;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.qing.pojo.User;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

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

@Controller
public class UserController {

    @GetMapping("/j3")
    @ResponseBody // 添加@ResponseBody，就不会走视图解析器
    public String json03() throws JsonProcessingException {
        List<User> list = new ArrayList<User>();
        User user1 = new User("张三丰","123456",999);
        User user2 = new User("张道陵","123456",999);
        list.add(user1);
        list.add(user2);
        return new ObjectMapper().writeValueAsString(list);
    }
}

fastjson

fastjson三个主要的类

测试 fastjson

pom.xml添加依赖

<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.76</version>
</dependency>

测试

package com.qing.controller;

import com.alibaba.fastjson.JSON;
import com.qing.pojo.User;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

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

@Controller
public class UserController {

    @GetMapping("/j4")
    @ResponseBody // 添加@ResponseBody，就不会走视图解析器
    public String json04() {
        List<User> list = new ArrayList<User>();
        User user1 = new User("张三丰","123456",999);
        User user2 = new User("张道陵","123456",999);
        list.add(user1);
        list.add(user2);
        return JSON.toJSONString(list);
    }
}

Java对象转json字符串

json字符串转Java对象

Java对象转json对象

json对象转Java对象

package com.qing.controller;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.qing.pojo.User;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

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

@Controller
public class UserController {

    @GetMapping("/j5")
    @ResponseBody // 添加@ResponseBody，就不会走视图解析器
    public String json05() {
        User user = new User("张三丰","123456",999);
        String jsonStr = JSON.toJSONString(user);
        System.out.println("Java对象转json字符串-->" + jsonStr);
        System.out.println("json字符串转Java对象-->" + JSON.parseObject(jsonStr, User.class));
        JSONObject jsonObject = (JSONObject) JSON.toJSON(user);
        System.out.println("Java对象转json对象-->" + jsonObject);
        System.out.println("json对象转Java对象-->" + JSON.toJavaObject(jsonObject, User.class));
        return JSON.toJSONString(user);
    }
}