GraphQL java send custom error in json format - json

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