java.io.IOException With Restful Web Service - spring

Question

I have a weird problem with my project. When i run main method in Client to create a User after send to Server then occur fllowing error:
Exception in thread "main" java.io.IOException: Server returned HTTP
response code: 400 for URL: http://localhost:8080/rest/user/create at
sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown
Source) at
sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown
Source) at
edu.java.spring.service.client.RestClientTest.createUser(RestClientTest.java:72)
at
edu.java.spring.service.client.RestClientTest.main(RestClientTest.java:30)
Here file RestClientTest.java
public class RestClientTest {
public static void main(String[] args) throws IOException{
// System.out.println("Rest Response" + loadUser("quypham"));
User user = new User();
user.setUserName("datpham");
user.setPassWord("12345");
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.YEAR,1960);
user.setBirthDay(calendar.getTime());
user.setAge(12);
createUser(user);
System.out.println("Rest Response" + loadUser("datpham"));
}
public static String createUser(User user) throws IOException{
URL url = new URL("http://localhost:8080/rest/user/create");
HttpURLConnection httpConnection = (HttpURLConnection) url.openConnection();
httpConnection.setRequestMethod("POST");
httpConnection.addRequestProperty("Content-Type","application/json");
httpConnection.addRequestProperty("Accept","application/json");
httpConnection.setDoOutput(true);
DataOutputStream wr = new DataOutputStream(httpConnection.getOutputStream());
ObjectMapper mapper = new ObjectMapper();
StringWriter writer = new StringWriter();
mapper.writeValue(writer,user);
wr.writeBytes(writer.getBuffer().toString());
wr.flush();
wr.close();
return readInputStream(httpConnection.getInputStream());
}
public static String readInputStream(InputStream stream) throws IOException{
StringWriter writer = new StringWriter();
try {
int read;
byte[] bytes = new byte[4*1024];
while ((read = stream.read(bytes))!=-1) {
writer.write(new String(bytes,0,read));
}
} finally {
// TODO: handle finally clause
stream.close();
writer.close();
}
return writer.getBuffer().toString();
}
Here file UserRestServiceController.java
#Controller
public class UserRestServiceController {
#Autowired
public UserDao userDao;
#RequestMapping(value = "/rest/user/create",method = RequestMethod.POST,consumes = MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.CREATED)
public void addUser(#RequestBody User user){
userDao.save(user);
}