Error response in json format for Spring interceptor - spring-mvc

Question

I am writing a REST based web service. I need to return all the responses as JSON format. I have an interceptor to validate my authentication parameters. On authentication failure scenario, I have to return the error response in JSON format.
Currently i am doing
response.setHeader("Content-Type","application/json");
response.sendError(HttpServletResponse.SC_UNAUTHORIZED, "{\"error\":\"Missing Authentication Parameters\"}");
The response body is coming as below.
JBoss Web/2.1.3.GA - Error report HTTP Status 401 - {"error":"Missing Authentication Parameters"}type Status reportmessage {"error":"Missing Authentication Parameters"}description This request requires HTTP authentication ({"error":"Missing Authentication Parameters"}).JBoss Web/2.1.3.GA
I need just the JSON string in response. Please help me.

Answer 1

You should probably be using spring-security for this. If you want to do it by hand, an alternative to using sendError on the response is to use spring MVC's #ExceptionHandler along with content negotiation to return JSON.
First define an error class*:
public class Error {
public message;
public exception;
public Error(String message, Exception ex) {
this.message = message;
this.exception = ex;
}
}
And an exception:
public class NotAuthenticatedException extends Exception {
// ...
}
Then in your controller you throw an exception at the appropriate time, catch it with #ExceptionHandler and return a ResponseEntity containing an Error instance and the appropriate error code.
#Controller
public class SimpleController {
#RequestMapping(...)
public String aMethod() {
// ...
throw new NotAuthenticatedException("Missing Authentication Parameters");
}
#ExceptionHandler(NotAuthenticatedException.class)
public ResponseEntity<Error> handleNotAuthenticatedException(
NotAuthenticatedException ex,
HttpServletRequest request) {
return new ResponseEntity<Error>(
new Error(ex.getMessage(), ex),
HttpStatus.UNAUTHORIZED
);
}
}
*use getters/setters to please the java convention gods