GraphQL java send custom error in json format

Question

I am working in an graphql application where I have to send custom error object / message in json irrespective of whether it occurs in servlet or service.

Expected error response

{ errorCode: 400 //error goes here, errorMessage: "my error mesage"}

It will be helpful if someone could guide me to achieve the above requirement.

Answer 1

GraphQL specification defines a clear format for the error entry in the response.

According to the spec, it should like this (assuming JSON format is used):

  "errors": [
    {
      "message": "Name for character with ID 1002 could not be fetched.",
      "locations": [ { "line": 6, "column": 7 } ],
      "path": [ "hero", "heroFriends", 1, "name" ]
      "extensions": {/* You can place data in any format here */}
    }
  ]

So you won't find a GraphQL implementation that allows you to extend it and return some like this in the GraphQL execution result, for example:

  "errors": [
    {
      "errorMessage": "Name for character with ID 1002 could not be fetched.",
      "errorCode": 404
    }
  ]

However, the spec lets you add data in whatever format in the extension entry. So you could create a custom Exception on the server side and end up with a response that looks like this in JSON:

  "errors": [
    {
      "message": "Name for character with ID 1002 could not be fetched.",
      "locations": [ { "line": 6, "column": 7 } ],
      "path": [ "hero", "heroFriends", 1, "name" ]
      "extensions": {
          "errorMessage": "Name for character with ID 1002 could not be fetched.",
          "errorCode": 404
      }
    }
  ]

It's quite easy to implement this on GraphQL Java, as described in the docs. You can create a custom exception that overrides the getExtensions method and create a map inside the implementation that will then be used to build the content of extensions:

public class CustomException extends RuntimeException implements GraphQLError {
    private final int errorCode;

    public CustomException(int errorCode, String errorMessage) {
        super(errorMessage);

        this.errorCode = errorCode;
    }

    @Override
    public Map<String, Object> getExtensions() {
        Map<String, Object> customAttributes = new LinkedHashMap<>();

        customAttributes.put("errorCode", this.errorCode);
        customAttributes.put("errorMessage", this.getMessage());

        return customAttributes;
    }

    @Override
    public List<SourceLocation> getLocations() {
        return null;
    }

    @Override
    public ErrorType getErrorType() {
        return null;
    }
}

then you can throw the exception passing in the code and message from inside your data fetchers:

throw new CustomException(400, "A custom error message");

Now, there is another way to tackle this.

Assuming you are working on a Web application, you can return errors (and data, for that matter) in whatever format that you want. Although that is a bit awkward in my opinion. GraphQL clients, like Apollo, adhere to the spec, so why would you want to return a response on any other format? But anyway, there are lots of different requirements out there.

Once you get a hold of an ExecutionResult, you can create a map or object in whatever format you want, serialise that as JSON and return this over HTTP.

Map<String, Object> result = new HashMap<>();

result.put("data", executionResult.getData());

List<Map<String, Object>> errors = executionResult.getErrors()
        .stream()
        .map(error -> {
            Map<String, Object> errorMap = new HashMap<>();

            errorMap.put("errorMessage", error.getMessage());
            errorMap.put("errorCode", 404); // get the code somehow from the error object

            return errorMap;
        })
        .collect(toList());

result.put("errors", errors);

// Serialize "result" and return that.

But again, having a response that doesn't comply with the spec doesn't make sense in most of the cases.