Controller返回JSON数据

使用jackson

导入jar包

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.10.6</version>
</dependency>

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">

    <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>

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 https://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 ">

    <!--注解扫描-->
    <context:component-scan base-package="com.starry.controller"></context:component-scan>

    <!--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"></constructor-arg>
            </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"></property>
                    </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/"></property>
        <!--后缀-->
        <property name="suffix" value=".jsp"></property>
    </bean>
</beans>

实体类

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
    

    private String name;
    private int age;
    private String sex;
}

Controller

---

json格式输出java对象

@Controller
public class UserController {
    

	@RequestMapping(value = "j1")
	@ResponseBody
	public String json1() throws JsonProcessingException {
    
	
	   User user = new User("繁星", 20, "男");
	
	   ObjectMapper objectMapper = new ObjectMapper();
	
	   String value = objectMapper.writeValueAsString(user);
	
	   return value;
   }
}

@ResponseBody : 不会走视图解析器,直接返回字符串
可在类上加注解@RestController相当于@Controller和@ResponseBody

输出结果

{
    "name":"繁星","age":20,"sex":"男"}

---

json格式输出集合

@RestController
public class UserController {
    

    @RequestMapping(value = "j2")
    public String json2() throws JsonProcessingException {
    

        User user1 = new User("繁星1", 20, "男");
        User user2 = new User("繁星2", 21, "男");
        User user3 = new User("繁星3", 22, "男");

        List<User> userList = new ArrayList<User>();
        userList.add(user1);
        userList.add(user2);
        userList.add(user3);

        return new ObjectMapper().writeValueAsString(userList);
    }
}

输出结果

[{
    "name":"繁星1","age":20,"sex":"男"},{
    "name":"繁星2","age":21,"sex":"男"},{
    "name":"繁星3","age":22,"sex":"男"}]

---

json格式输出时间

@RequestMapping("/j3")
public String json3() throws JsonProcessingException {
    

    ObjectMapper mapper = new ObjectMapper();

    //创建时间一个对象，java.util.Date
    Date date = new Date();
    //将对象解析成为json格式
    String str = mapper.writeValueAsString(date);
    return str;
}

输出结果为时间戳,Jackson 默认是会把时间转成timestamps形式

取消timestamps形式 ， 自定义时间格式

@RequestMapping(value = "j3")
public String json3() throws JsonProcessingException {
    

    Date date = new Date();

    ObjectMapper objectMapper = new ObjectMapper();
    //配置不使用时间戳
    objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
    //自定义日期格式
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    //设置日期格式
    objectMapper.setDateFormat(simpleDateFormat);


    return objectMapper.writeValueAsString(date);
}

输出结果

"2021-04-08 11:19:46"

使用FastJson

导入依赖

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.1.37</version>
</dependency>

Controller

@RequestMapping(value = "j4")
public String json4() throws JsonProcessingException {
    

    User user1 = new User("繁星1", 20, "男");
    User user2 = new User("繁星2", 21, "男");
    User user3 = new User("繁星3", 22, "男");

    List<User> userList = new ArrayList<User>();
    userList.add(user1);
    userList.add(user2);
    userList.add(user3);


    String userJosn = JSON.toJSONString(user1);
    String userListJson = JSON.toJSONString(userList);


    System.out.println("java对象转json字符串");
    System.out.println(userJosn);
    System.out.println("集合转json字符串");
    System.out.println(userListJson);

    User user = JSON.parseObject(userJosn, User.class);
    List<User> userList1 = JSON.parseArray(userListJson,User.class);


    System.out.println("json字符串转java对象");
    System.out.println(user);
    System.out.println("json字符串转集合");
    for (User userOne : userList1) {
    
        System.out.println(userOne);
    }


    return "testFastJson";
}

输出结果

java对象转json字符串
{
    "age":20,"name":"繁星1","sex":"男"}
集合转json字符串
[{
    "age":20,"name":"繁星1","sex":"男"},{
    "age":21,"name":"繁星2","sex":"男"},{
    "age":22,"name":"繁星3","sex":"男"}]
json字符串转java对象
User(name=繁星1, age=20, sex=男)
json字符串转集合
User(name=繁星1, age=20, sex=男)
User(name=繁星2, age=21, sex=男)
User(name=繁星3, age=22, sex=男)