SpringMVC 使用@ResponseBody返回json

1：关于web.xml配置

<?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">
    
    <!--spring配置文件-->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
    </context-param>
    <!--使用ContextLoaderListener启动spring配置文件-->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
    <!--启动servlet-->
    <servlet>
        <servlet-name>dispacth</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <!--servlet映射-->
    <servlet-mapping>
        <servlet-name>dispacth</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

2：关于dispacth-servlet.xml配置

<?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:p="http://www.springframework.org/schema/p"
       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-4.3.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd">

    <context:component-scan base-package="com.smart.web"/>
    <!--一定要加，否则在使用@ResponseBody注解会异常-->
    <mvc:annotation-driven/>
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>

</beans>

3：顺便记录下applicationContext.xml配置，使用了Hibernate

<?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:p="http://www.springframework.org/schema/p"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/tx
       http://www.springframework.org/schema/tx/spring-tx.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context-4.3.xsd">

    <!--自动扫描注解-->
    <context:component-scan base-package="com.smart.dao"/>

    <!--jdbc操作数据库-->
    <bean id="jdbcTemplate"
          class="org.springframework.jdbc.core.JdbcTemplate"
          p:dataSource-ref="jdbcDataSource"/>
    <!--jdbc处理图片lob，text等类型-->
    <bean id="lobHandler"
          class="org.springframework.jdbc.support.lob.DefaultLobHandler"
          lazy-init="true"/>
    <!--定义一个jdbc数据源，创建一个驱动管理数据源的bean -->
    <bean id="jdbcDataSource"
          class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/myTest" />
        <property name="username" value="root" />
        <property name="password" value="wfx123456" />
    </bean>
    <!--hibernate-->
    <bean id="sessionFactory"
          class="org.springframework.orm.hibernate5.LocalSessionFactoryBean"
          p:dataSource-ref="jdbcDataSource"
          p:packagesToScan="com.smart.dao">
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
                <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
    </bean>

    <!--配置HibernateTemplate Bean 对象操作数据库-->
    <bean id="hibernateTemplate"
          class="org.springframework.orm.hibernate5.HibernateTemplate"
          p:sessionFactory-ref="sessionFactory"/>
    <!--配置Hibernate事务管理器-->
    <bean id="transactionManage"
          class="org.springframework.orm.hibernate5.HibernateTransactionManager"
          p:sessionFactory-ref="sessionFactory"/>
    <tx:annotation-driven transaction-manager="transactionManage"/>
</beans>

4：使用mvc返回json，需要依赖以下库，注意库的版本，可能会冲突

<!--使用mvc返回json，需要导入以下库-->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version> ${jackson-core.version} </version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version> ${jackson-databind.version} </version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version> ${jackson-annotations.version} </version>
        </dependency>

5：一直出现错误

org.springframework.http.converter.HttpMessageNotWritableException: No converter found for return value of type: class java.util.HashMap

将maven的库全部删除，然后重新加入一遍，如图：

image.png

重新配置tomcat

image.png

6：返回json

@RequestMapping(value = "/showUserListByJson")
    @ResponseBody
    public Map<String, Object> showUserListInJson(ModelMap mm) {
        User user = (User) mm.get("user");
        user.setUserId(1);
        user.setUserName("2");
        ArrayList<User> list = new ArrayList<User>();
        list.add(user);
        Map<String, Object> mapMode = new HashMap<String, Object>();
        mapMode.put("userList", list);
        mapMode.put("word", "研发");

        return mapMode;
    }

7：结果

image.png