Java Web(11) Spring MVC 返回Json

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd">
<context:annotation-config/>

<mvc:annotation-driven />
</beans>

<properties>
<jackson.version>2.7.3</jackson.version>
</properties>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>${jackson.version}</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>${jackson.version}</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>${jackson.version}</version>
</dependency>

package controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpSession;
import java.util.HashMap;
import java.util.Map;
@Controller
public class JsonUserExistsController {

private Boolean flag ;
private String message;
@RequestMapping(value="json/test",
produces = MediaType.APPLICATION_JSON_VALUE)
public
@ResponseBody Map<String,String>
userchecking(@RequestParam Map<String,String> params,HttpSession session){
Map<String,String> json = new HashMap<String,String>();
String imageWord = params.get("imgcode");
String session_word = (String) session.getAttribute("image_word");
if(!session_word.equals(imageWord)){
flag = false;
message = "验证码错误";
json.put("flag",flag.toString());
json.put("message",message);
return json;
}
}
}

{"flag":"false","message":"验证码错误"}