REST service: The proper way of returning exception

Question

I use Jersey API for my REST service. My question is: Is there a more elegant way of returning exceptions in a JSON form? Is it better to concern myself with creating a json object myself and attaching it to the response directly?

This is a simplified example of one of the methods in the service. As you see, I use HashMap only because the method may throw an exception, in which case I need to return information about It.

@Path("/admin")
public class AdminService {

    @Context
    HttpServletRequest request;

    @POST
    @Produces(MediaType.APPLICATION_JSON)
    public Map<Integer, String> createCompany(Company company){

        Map<Integer, String> map = new HashMap<>();
        try{
            AdminFacade adminFacade = (AdminFacade)Utility.getFacade(request);
            adminFacade.createCompany(company);
            map.put(1,"success");
        } catch (ExceptionREST e) {
            map.put(e.getErrorNumber(), e.getMessage());
        } finally {
            return map;
        }
    }
}

Answer 1

You can create a class like the one below to represent an error,

@JsonPropertyOrder({ "code", "field", "message" })
public class ErrorInfo {

    private String code;

    private String field;

    private String message;

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getField() {
        return field;
    }

    public void setField(String field) {
        this.field = field;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

}

You can create a class which extends an exception like this,

public class InvalidInputException extends RuntimeException {

    private static final long serialVersionUID = -5027121014723838738L;

    private List<ErrorInfo> errors;

    public List<ErrorInfo> getErrors() {
        return this.errors;
    }

    public InvalidInputException(List<ErrorInfo> errors) {
        super();
        this.errors = errors;
    }

    public InvalidInputException(String message, List<ErrorInfo> errors) {
        super(message);
        this.errors = errors;
    }

}

And have a exception mapper, where you can convert the List to json and return to the user with http status code 400 (Bad Request).

@Provider
public class InvalidInputExceptionMapper implements ExceptionMapper<InvalidInputException> {

    @Override
    @Produces(MediaType.APPLICATION_JSON)
    public Response toResponse(InvalidInputException e) {

        ResponseBuilder rb = Response.status(Status.BAD_REQUEST);

        rb.entity(e.getErrors());
        return rb.build();   
    }
}

Http Response will be,

HTTP/1.1 400 BAD REQUEST
{
"errors": [{
    "error": {
        "code": "100",
        "field": null,
        "message": "Name is required"
    },
    "error": {
        "code": "100",
        "field": null,
        "message": "Age is required"
    }
}]

}

Answer 2

I believe it is quite popular that people use http response status code to handle the error. E.g. 404 status is not found 5xx is server internal error e.t.c. You can easily set the error code by using the Response object. Instead of returning a map, return a Response object.

@Path("/admin")public class AdminService {

@Context
HttpServletRequest request;

@POST
@Produces(MediaType.APPLICATION_JSON)
public Response createCompany(Company company){

    Map<Integer, String> map = new HashMap<>();
    try{
        AdminFacade adminFacade = (AdminFacade)Utility.getFacade(request);
        Company commpany=adminFacade.createCompany(company);//this entity annotated by XmlRootElement
        Response response=Response.ok().entity(company).build();
    } catch (ExceptionREST e) {
        response=Response.status(404).build();
    } return response;
}}

To make the Restful api more robust, some will return an OK response to prevent "smart redirect" from the server and output some weird html. you can refer here for a list of http status code and what it mean. For Java EE Response class, you can refer the official javadoc