java.lang.IllegalArgumentException: No converter found for return value of type

访问链接http://localhost:8080/test/user，若报错java.lang.IllegalArgumentException: No converter found for return value of type,则是UserEntity类中缺少getter/setter方法

<!--jackson-->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.7.0</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.7.0</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.7.0</version>
        </dependency>

package com.hundsun.test.entity;

public class UserEntity {

    private String username;
    private String password;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public UserEntity(){

    }

    public UserEntity(String username, String password){
        this.username = username;
        this.password = password;
    }
}

package com.hundsun.test.controller;

import com.hundsun.test.entity.UserEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
@RequestMapping("/test")//Contoller下所有接口统一入口
public class UserController {

    //映射一个action
    @RequestMapping("/user")
    @ResponseBody//表示直接输出返回内容，不进行jsp或html跳转，本例是为了写接口，这里直接返回json
    public UserEntity getUser() {
        //创建一个UserEntity，直接返回，之前在web.xml中配置的jackson会将user对象转为json输出
        UserEntity user = new UserEntity("jack", "123456");
        return user;
    }

}