SpringMVC之JSON使用

前后端数据之间的交互一般都是采用json格式，那json格式到底是什么样的？

json格式为用{“var1”:"value1","var2":"value2"}，采用的是键值对的形式，每个参数和值都使用“”包裹，相邻参数用逗号隔开。

1、使用json首先要导入json依赖：

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.12.0</version>
        </dependency>

2、编写web.xml文件

<?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>


</web-app>

3、编写spring配置文件，这里面增加了json乱码解决方法

<?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">

    <context:component-scan base-package="com.lizheng.controller"/>
    <mvc:default-servlet-handler/>
<!--    注解生效以及解决json乱码问题-->
    <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>


    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>

</beans>

4、controller类：这里使用了@RestController 注解，表示这个类的返回值不会被视图解析器解析

@RestController
public class UserController {

    @RequestMapping("/j1")
    public String json1() throws JsonProcessingException {

        ObjectMapper mapper = new ObjectMapper();

        User user = new User(1,"rourou",2);

        return mapper.writeValueAsString(user);
    }

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

        List<User> userList = new ArrayList<>();
        User user1 = new User(1, "肉肉", 2);
        User user2 = new User(2, "肉肉", 2);
        User user3 = new User(3, "肉肉", 2);
        User user4 = new User(4, "肉肉", 2);

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

        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(userList);

    }
}

 5、运行结果