3.4 JSON交互处理 - JSON - 《Java企业级框架》

一、什么是JSON
二、Jackson的使用
三、Fastjson的使用

一、什么是JSON

JSON(JavaScript Object Notation, JS 对象标记) 是一种轻量级的数据交换格式，目前使用特别广泛。
采用完全独立于编程语言的文本格式来存储和表示数据。
简洁和清晰的层次结构使得 JSON 成为理想的数据交换语言。
易于人阅读和编写，同时也易于机器解析和生成，并有效地提升网络传输效率。

在 JavaScript 语言中，一切都是对象。因此，任何JavaScript 支持的类型都可以通过 JSON 来表示，例如字符串、数字、对象、数组等。看看他的要求和语法格式：

对象表示为键值对，数据由逗号分隔
花括号保存对象
方括号保存数组

JSON 键值对是用来保存 JavaScript 对象的一种方式，和 JavaScript 对象的写法也大同小异，键/值对组合中的键名写在前面并用双引号 “” 包裹，使用冒号 : 分隔，然后紧接着值

var obj = {a: 'Hello', b: 'World'}; //这是一个对象，注意键名也是可以使用引号包裹的
var json = '{"a": "Hello", "b": "World"}'; //这是一个 JSON 字符串，本质是一个字符串

二、Jackson的使用

配置环境

<!--导入jackson依赖-->
<dependencies>
  <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
  </dependency>
</dependencies>

<?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">

    <servlet>
        <servlet-name>SpringMVC</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-servlet.xml</param-value>
        </init-param>
    </servlet>

    <servlet-mapping>
        <servlet-name>SpringMVC</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>encodingFilter</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>encodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

</web-app>

<?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">

    <context:component-scan base-package="com.comprehensive.controller"/>
    <mvc:default-servlet-handler/>
    <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>

package com.comprehensive.pojo;

public class User {
    private String name;
    private int age;
    private String sex;

    public User() {}

    public User(String name, int age, String sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                '}';
    }
}

Jackson测试(普通类)

package com.comprehensive.controller;

import com.comprehensive.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
@RequestMapping("/user")
public class UserController {
    @ResponseBody //
    @RequestMapping("/jackson_test")
    public String test() throws JsonProcessingException {
        User user = new User("李杰亮", 22, "男");
        // Jackson，ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        String str = mapper.writeValueAsString(user);
        return str;
    }
}

{"name":"???","age":22,"sex":"?"}

解决乱码问题

方式一

package com.comprehensive.controller;

import com.comprehensive.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
@RequestMapping("/user")
public class UserController {
    @ResponseBody //不会走视图解析器
    @RequestMapping(value = "/jackson_test", produces = "application/json;charset=utf-8")
    public String test() throws JsonProcessingException {
        User user = new User("李杰亮", 22, "男");
        // Jackson，ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        String str = mapper.writeValueAsString(user);
        return str;
    }
}

{"name":"李杰亮","age":22,"sex":"男"}

方式二

<?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">

    <context:component-scan base-package="com.comprehensive.controller"/>
    <mvc:default-servlet-handler/>
    <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>

    <!-- 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>

{"name":"李杰亮","age":22,"sex":"男"}

注意点

在类上直接使用 @RestController ，这样子，里面所有的方法都只会返回 json 字符串了，不用再每一个都添加@ResponseBody ！我们在前后端分离开发中，一般都使用 @RestController ，十分便捷！

Jackson测试(集合)

package com.comprehensive.controller;

import com.comprehensive.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;

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

@Controller
@RequestMapping("/user")
public class UserController {
    @ResponseBody //不会走视图解析器
    @RequestMapping("/jackson_test")
    public String test() throws JsonProcessingException {
        User user1 = new User("李杰亮", 22, "男");
        User user2 = new User("何光伦", 21, "男");
        User user3 = new User("焦锦标", 22, "男");
        List<User> userList = new ArrayList<User>();
        userList.add(user1);
        userList.add(user2);
        userList.add(user3);
        // Jackson，ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        String str = mapper.writeValueAsString(userList);
        return str;
    }
}

[{"name":"李杰亮","age":22,"sex":"男"},{"name":"何光伦","age":21,"sex":"男"},{"name":"焦锦标","age":22,"sex":"男"}]

Jackson测试(时间)

package com.comprehensive.controller;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import java.text.SimpleDateFormat;
import java.util.Date;

@Controller
@RequestMapping("/user")
public class UserController {
    @ResponseBody //不会走视图解析器
    @RequestMapping("/jackson_test")
    public String test() throws JsonProcessingException {
        Date date = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        // Jackson，ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        mapper.setDateFormat(sdf);
        //不使用时间戳的方式
        //mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        String str = mapper.writeValueAsString(date);
        return str;
    }
}

三、Fastjson的使用

导入依赖

<dependency>
   <groupId>com.alibaba</groupId>
   <artifactId>fastjson</artifactId>
   <version>1.2.60</version>
</dependency>

Fastjson测试(普通类)

@Controller
@RequestMapping("/user")
public class UserController {
    @ResponseBody
    @RequestMapping("/fastjson_test")
    public String test2() {
        return JSON.toJSONString(new User("李杰亮", 22, "男"));
    }
}

{"age":22,"name":"李杰亮","sex":"男"}

Fastjson测试(集合)

@Controller
@RequestMapping("/user")
public class UserController {
    @ResponseBody
    @RequestMapping("/fastjson_test")
    public String test2() {
        List<User> userList = new ArrayList<User>();
        userList.add(new User("李杰亮", 22, "男"));
        userList.add(new User("何光伦", 21, "男"));
        userList.add(new User("焦锦彪", 22, "男"));
        return JSON.toJSONString(userList);
    }
}

[{"age":22,"name":"李杰亮","sex":"男"},{"age":21,"name":"何光伦","sex":"男"},{"age":22,"name":"焦锦彪","sex":"男"}]

Fastjson测试(时间)

@Controller
@RequestMapping("/user")
public class UserController {
    @ResponseBody
    @RequestMapping("/fastjson_test")
    public String test2() {
        Date date = new Date();
        return JSON.toJSONStringWithDateFormat(date, "yyyy-MM-dd HH:mm:ss");
    }
}