springmvc后端接收json415错误

配置文件

     <mvc:annotation-driven>
        <mvc:message-converters>
            <bean class="org.springframework.http.converter.StringHttpMessageConverter"/>
            <bean class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
                <property name="supportedMediaTypes">
                    <list>
                        <value>text/html;charset=UTF-8</value>
                        <value>application/json;charset=UTF-8</value>
                    </list>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

后端接收代码

     @RequestMapping(value = "/json")
    public String json(@RequestBody User user) {
        System.out.println(user.getName());
        System.out.println(user.getAge());
        return "index";
    }

出现了415错误，求助

代码没贴全，怎么看