SpringMVC 访问Controller 报错：e No converter found for return value of type: class java.util.ArrayLis

1、controller方法如下：

@RequestMapping("/a2")
public  List<User>    ajaxtest(){
    List<User> userList = new ArrayList<User>();
    userList.add(new User("妗妗1",1,"女"));
    userList.add(new User("妗妗12",2,"女"));
    userList.add(new User("妗妗13",3,"女"));
    User user4 = new User("妗妗14",1,"女");
    System.out.println(userList);

    return userList;
}

2、请求该方法，返回如下信息

3、经查明，是controller 不支持直接返回对象，可将java对象，转为json对象，再返回。

导入json包，并配置对象转换成json对象的配置后，可直接返回对象，具体步骤如下

（1）导入jackjson包

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->

<dependency>

<groupId>com.fasterxml.jackson.core</groupId>

<artifactId>jackson-databind</artifactId>

<version>2.9.8</version>

</dependency>

（2）配置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>

4、再次方法该方法，正常。

@RequestMapping("/a2")
public List<User> ajaxtest(){
List<User> userList = new ArrayList<User>();
userList.add(new User("妗妗1",1,"女"));
userList.add(new User("妗妗12",2,"女"));
userList.add(new User("妗妗13",3,"女"));
User user4 = new User("妗妗14",1,"女");
System.out.println(userList);

return userList;
}