Handling custom error response in JAX-RS 2.0 client library

Question

I am starting to use the new client API library in JAX-RS and really loving it so far. I have found one thing I cannot figure out however. The API I am using has a custom error message format that looks like this for example:

{
    "code": 400,
    "message": "This is a message which describes why there was a code 400."
} 

It returns 400 as the status code but also includes a descriptive error message to tell you what you did wrong.

However the JAX-RS 2.0 client is re-mapping the 400 status into something generic and I lose the good error message. It correctly maps it to a BadRequestException, but with a generic "HTTP 400 Bad Request" message.

javax.ws.rs.BadRequestException: HTTP 400 Bad Request
    at org.glassfish.jersey.client.JerseyInvocation.convertToException(JerseyInvocation.java:908)
    at org.glassfish.jersey.client.JerseyInvocation.translate(JerseyInvocation.java:770)
    at org.glassfish.jersey.client.JerseyInvocation.access$500(JerseyInvocation.java:90)
    at org.glassfish.jersey.client.JerseyInvocation$2.call(JerseyInvocation.java:671)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:228)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:424)
    at org.glassfish.jersey.client.JerseyInvocation.invoke(JerseyInvocation.java:667)
    at org.glassfish.jersey.client.JerseyInvocation$Builder.method(JerseyInvocation.java:396)
    at org.glassfish.jersey.client.JerseyInvocation$Builder.get(JerseyInvocation.java:296)

Is there some sort of interceptor or custom error handler that can be injected so that I get access to the real error message. I've been looking through documentation but can't see any way of doing it.

I am using Jersey right now, but I tried this using CXF and got the same result. Here is what the code looks like.

Client client = ClientBuilder.newClient().register(JacksonFeature.class).register(GzipInterceptor.class);
WebTarget target = client.target("https://somesite.com").path("/api/test");
Invocation.Builder builder = target.request()
                                   .header("some_header", value)
                                   .accept(MediaType.APPLICATION_JSON_TYPE)
                                   .acceptEncoding("gzip");
MyEntity entity = builder.get(MyEntity.class);

UPDATE:

I implemented the solution listed in the comment below. It is slightly different since the classes have changed a bit in the JAX-RS 2.0 client API. I still think it is wrong that the default behavior is to give a generic error message and discard the real one. I understand why it wouldn't parse my error object, but the un-parsed version should have been returned. I end up having the replicate exception mapping that the library already does.

Thanks for the help.

Here is my filter class:

@Provider
public class ErrorResponseFilter implements ClientResponseFilter {

    private static ObjectMapper _MAPPER = new ObjectMapper();

    @Override
    public void filter(ClientRequestContext requestContext, ClientResponseContext responseContext) throws IOException {
        // for non-200 response, deal with the custom error messages
        if (responseContext.getStatus() != Response.Status.OK.getStatusCode()) {
            if (responseContext.hasEntity()) {
                // get the "real" error message
                ErrorResponse error = _MAPPER.readValue(responseContext.getEntityStream(), ErrorResponse.class);
                String message = error.getMessage();

                Response.Status status = Response.Status.fromStatusCode(responseContext.getStatus());
                WebApplicationException webAppException;
                switch (status) {
                    case BAD_REQUEST:
                        webAppException = new BadRequestException(message);
                        break;
                    case UNAUTHORIZED:
                        webAppException = new NotAuthorizedException(message);
                        break;
                    case FORBIDDEN:
                        webAppException = new ForbiddenException(message);
                        break;
                    case NOT_FOUND:
                        webAppException = new NotFoundException(message);
                        break;
                    case METHOD_NOT_ALLOWED:
                        webAppException = new NotAllowedException(message);
                        break;
                    case NOT_ACCEPTABLE:
                        webAppException = new NotAcceptableException(message);
                        break;
                    case UNSUPPORTED_MEDIA_TYPE:
                        webAppException = new NotSupportedException(message);
                        break;
                    case INTERNAL_SERVER_ERROR:
                        webAppException = new InternalServerErrorException(message);
                        break;
                    case SERVICE_UNAVAILABLE:
                        webAppException = new ServiceUnavailableException(message);
                        break;
                    default:
                        webAppException = new WebApplicationException(message);
                }

                throw webAppException;
            }
        }
    }
}

Answer 1

I believe you want to do something like this:

Response response = builder.get( Response.class );
if ( response.getStatusCode() != Response.Status.OK.getStatusCode() ) {
    System.out.println( response.getStatusType() );
    return null;
}

return response.readEntity( MyEntity.class );

Another thing you can try (since I don't know where this API puts stuff -- i.e. in the header or entity or what) is:

Response response = builder.get( Response.class );
if ( response.getStatusCode() != Response.Status.OK.getStatusCode() ) {
    // if they put the custom error stuff in the entity
    System.out.println( response.readEntity( String.class ) );
    return null;
}

return response.readEntity( MyEntity.class );

If you would like to generally map REST response codes to Java exception you can add a client filter to do that:

class ClientResponseLoggingFilter implements ClientResponseFilter {

    @Override
    public void filter(final ClientRequestContext reqCtx,
                       final ClientResponseContext resCtx) throws IOException {

        if ( resCtx.getStatus() == Response.Status.BAD_REQUEST.getStatusCode() ) {
            throw new MyClientException( resCtx.getStatusInfo() );
        }

        ...

In the above filter you can create specific exceptions for each code or create one generic exception type that wraps the Response code and entity.

Answer 2

There are other ways to getting a custom error message to the Jersey client besides writing a custom filter. (although the filter is an excellent solution)

1) Pass error message in an HTTP header field. The detail error message could be in the JSON response and in an additional header field, such as "x-error-message".

The Server adds the HTTP error header.

ResponseBuilder rb = Response.status(respCode.getCode()).entity(resp);
if (!StringUtils.isEmpty(errMsg)){
    rb.header("x-error-message", errMsg);
}
return rb.build();

The Client catches the exception, NotFoundException in my case, and reads the response header.

try {
    Integer accountId = 2222;
    Client client = ClientBuilder.newClient();
    WebTarget webTarget = client.target("http://localhost:8080/rest-jersey/rest");
    webTarget = webTarget.path("/accounts/"+ accountId);
    Invocation.Builder ib = webTarget.request(MediaType.APPLICATION_JSON);
    Account resp = ib.get(new GenericType<Account>() {
    });
} catch (NotFoundException e) {
    String errorMsg = e.getResponse().getHeaderString("x-error-message");
    // do whatever ...
    return;
}

2) Another solution is to catch the exception and read the response content.

try {
    // same as above ...
} catch (NotFoundException e) {
    String respString = e.getResponse().readEntity(String.class);
    // you can convert to JSON or search for error message in String ...
    return;
} 

Answer 3

The class WebApplicationException was designed for that but for some reason it ignores and overwrites what you specify as parameter for the message.

For that reason I created my own extension WebAppException that honors the parameters. It is a single class and it doesn't require any response filter or a mapper.

I prefer exceptions than creating a Response as it can be thrown from anywhere while processing.

Simple usage:

throw new WebAppException(Status.BAD_REQUEST, "Field 'name' is missing.");

The class:

import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.Response.Status;
import javax.ws.rs.core.Response.Status.Family;
import javax.ws.rs.core.Response.StatusType;

public class WebAppException extends WebApplicationException {
    private static final long serialVersionUID = -9079411854450419091L;

    public static class MyStatus implements StatusType {
        final int statusCode;
        final String reasonPhrase;

        public MyStatus(int statusCode, String reasonPhrase) {
            this.statusCode = statusCode;
            this.reasonPhrase = reasonPhrase;
        }

        @Override
        public int getStatusCode() {
            return statusCode;
        }
        @Override
        public Family getFamily() {
            return Family.familyOf(statusCode);
        }
        @Override
        public String getReasonPhrase() {
            return reasonPhrase;
        }
    }

    public WebAppException() {
    }

    public WebAppException(int status) {
        super(status);
    }

    public WebAppException(Response response) {
        super(response);
    }

    public WebAppException(Status status) {
        super(status);
    }

    public WebAppException(String message, Response response) {
        super(message, response);
    }

    public WebAppException(int status, String message) {
        super(message, Response.status(new MyStatus(status, message)). build());
    }

    public WebAppException(Status status, String message) {
        this(status.getStatusCode(), message);
    }

    public WebAppException(String message) {
        this(500, message);
    }

}