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.

Answer 2

The other posted answer didn't work for me. I found a solution by creating the following classes:

1) A throwable CustomException of GraphQLError type (just like mentioned in another answer).

2) Creating a GraphQLError Adaptor, which is not a Throwable.

3) A custom GraphQLErrorHandler to filter the custom exception.

Step 1:
The below throwable CustomGraphQLException implements GraphQLError because the GraphQLErrorHandler interface accepts errors only of type GraphQLError.

public class CustomGraphQLException extends RuntimeException implements GraphQLError {

    private final int errorCode;
    private final String errorMessage;

    public CustomGraphQLException(int errorCode, String errorMessage) {
        super(errorMessage);
        this.errorCode = errorCode;
        this.errorMessage = errorMessage;
    }

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

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

    @Override
    public String getMessage() {
        return this.errorMessage;
    }

    @Override
    public Map<String, Object> getExtensions() {
        Map<String, Object> customAttributes = new HashMap<>();
        customAttributes.put("errorCode", this.errorCode);
        customAttributes.put("errorMessage", this.getMessage());
        return customAttributes;
    }
}

Step 2:
A non-throwable adaptor of GraphQLError is created to avoid the stack-trace of the above custom exception being passed in the final GraphQL Error Response.

public class GraphQLErrorAdaptor implements GraphQLError {

    private final GraphQLError graphQLError;

    public GraphQLErrorAdaptor(GraphQLError graphQLError) {
        this.graphQLError = graphQLError;
    }

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

    @Override
    public ErrorType getErrorType() {
        return graphQLError.getErrorType();
    }

    @Override
    public String getMessage() {
        return graphQLError.getMessage();
    }

    @Override
    public Map<String, Object> getExtensions() {
        return graphQLError.getExtensions();
    }
}

Step 3:
A custom GraphQLErrorHandler is implemented to filter the custom CustomGraphQLException and avoid its replacement with the default graphQL error response.

public class CustomGraphQLErrorHandler implements GraphQLErrorHandler {

    public CustomGraphQLErrorHandler() { }

    public List<GraphQLError> processErrors(List<GraphQLError> errors) {
        List<GraphQLError> clientErrors = this.filterGraphQLErrors(errors);
        List<GraphQLError> internalErrors = errors.stream()
                .filter(e -> isInternalError(e))
                .map(GraphQLErrorAdaptor::new)
                .collect(Collectors.toList());

        if (clientErrors.size() + internalErrors.size() < errors.size()) {
            clientErrors.add(new GenericGraphQLError("Internal Server Error(s) while executing query"));
            errors.stream().filter((error) -> !this.isClientError(error)
            ).forEach((error) -> {
                if (error instanceof Throwable) {
                    LOG.error("Error executing query!", (Throwable) error);
                } else {
                    LOG.error("Error executing query ({}): {}", error.getClass().getSimpleName(), error.getMessage());
                }

            });
        }
        List<GraphQLError> finalErrors = new ArrayList<>();
        finalErrors.addAll(clientErrors);
        finalErrors.addAll(internalErrors);

        return finalErrors;
    }

    protected List<GraphQLError> filterGraphQLErrors(List<GraphQLError> errors) {
        return errors.stream().filter(this::isClientError).collect(Collectors.toList());
    }

    protected boolean isClientError(GraphQLError error) {
        return !(error instanceof ExceptionWhileDataFetching) && !(error instanceof Throwable);
    }

    protected boolean isInternalError(GraphQLError error) {
        return (error instanceof ExceptionWhileDataFetching) &&
                (((ExceptionWhileDataFetching) error).getException() instanceof CustomGraphQLException);
    }

}

Step 4: Configure the CustomGraphQLErrorHandler in GraphQLServlet. I am assuming you are using spring-boot for this step.

@Configuration
public class GraphQLConfig {

    @Bean
    public ServletRegistrationBean graphQLServletRegistrationBean(
            QueryResolver queryResolver,
            CustomGraphQLErrorHandler customGraphQLErrorHandler) throws Exception {

        GraphQLSchema schema = SchemaParser.newParser()
                .schemaString(IOUtils.resourceToString("/library.graphqls", Charset.forName("UTF-8")))
                .resolvers(queryResolver)
                .build()
                .makeExecutableSchema();

        return new ServletRegistrationBean(new SimpleGraphQLServlet(schema,
                new DefaultExecutionStrategyProvider(), null, null, null,
                customGraphQLErrorHandler, new DefaultGraphQLContextBuilder(), null,
                null), "/graphql");

    }

}

Reference