一、Controller返回JSON数据

• Jackson应该是目前比较好的json解析工具了
• 当然工具不止这个，比如还有阿里巴巴的fastjson等等。
• 们这里使用Jackson,使用它需要导入它的jar包;

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.13.3</version>
</dependency>
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• 配置SpringMVC需要的配置
  web. xmI

<?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>
        <load-on-startup>1</load-on-startup>
    </servlet>

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

    <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>
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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
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">

    <!--自动扫描包-->
    <context:component-scan base-package="com.massimo.controller"/>

    <!--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>
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• 编写一个User的实体类，然后去编写测试Controller;
  User实体类：

package com.massimo.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 + '\'' +
                '}';
    }
}

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UserController：

package com.massimo.controller;

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

@Controller
public class UserController {

    @RequestMapping("/j1")
    @ResponseBody //加了这个注解，它就不会走视图解析器，会直接返回一个字符串
    public String json1() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();

        //创建一个对象
        User user = new User("马西莫",20,"男");
        String str = mapper.writeValueAsString(user);
        return str;
    }
}

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• 配置Tomcat，启动测试

• 发现出现了乱码问题，我们需要设置一下他的编码格式为utf-8, 以及它返回的类型；
• 通过@RequestMaping的produces属性来实现，修改下代码

@RequestMapping(value = "/j1",produces = "application/json;charset=utf-8")
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• 再次测试，效果如下：
  

二、代码优化

乱码统一解决

上一种方法比较麻烦，如果项目中有许多请求则每一个都要添加，可以通过Spring配置统一指定，这样就不用每次都去处理了!

我们可以在springmvc的配置文件上添加一段消息StringHttpMessageConverter转换配置!

<!--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>
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不用@RequestMaping的produces属性来测试，效果如下：

@Controller与@RestController的区别：

• @Controller会走视图解析器
• @RestController会返回字符串

三、测试

3.1、集合测试

@RequestMapping("/j2")
    @ResponseBody
    public String json2() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        List<User> userList = new ArrayList<User>();

        User user1 = new User("Massimo1", 20, "男");
        User user2 = new User("Massimo2", 20, "男");
        User user3 = new User("Massimo3", 20, "男");
        User user4 = new User("Massimo4", 20, "男");

        userList.add(user1);
        userList.add(user2);
        userList.add(user3);
        userList.add(user4);

        String str = mapper.writeValueAsString(userList);
        return str;
    }
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效果：

3.2、时间测试一

 @RequestMapping("/j3")
    @ResponseBody
    public String json3() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        Date date = new Date();
        //自定义日期的格式
        SimpleDateFormat sdf = 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(sdf.format(date));
    }
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效果：

3.3、时间测试二

@RequestMapping("/j4")
    @ResponseBody
    public String json4() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        //不使用时间戳的方式
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
        //自定义日期的格式
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        mapper.setDateFormat(sdf);
        Date date = new Date();
        //ObjectMapper,时间解析后的默认格式为：Timestamp，时间戳
        return mapper.writeValueAsString(date);
    }
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效果：

3.4、封装工具类

package com.massimo.utils;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.text.SimpleDateFormat;

public class JsonUtils {
    
    public static String getJson(Object object){
        return getJson(object,"yyyy-MM-dd HH:mm:ss");
    }
    
    public static String getJson(Object object,String dateFormat){
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
        SimpleDateFormat sdf = new SimpleDateFormat(dateFormat);
        mapper.setDateFormat(sdf);

        try {
            return mapper.writeValueAsString(object);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return null;
    }
}

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