Note: 4.2 is the newest 4.x version

Thanks a lot to all contributors for reporting bugs, giving feedback, fixing bugs, adding new features and more!

Major New features:

#590
This is the biggest enhancement to come to graphql-java in a long time. Query execution is now performed in a fully asynchronous manner. A DataFetcher is now able to return a CompletionStage<Object> background promise to data and the graphql-java engine will ensure that when it completes it will be placed into the correct place in the query results.

This allows you to use facilities like java 8's CompletableFuture.supplyAsync() to run many data fetchers in parallel, which should improve the speed of your system by fully utilizing all your available CPUs.

All of the provided ExecutionStrategy implementations now support fully asynchronous results. Note if you have your own derived ExecutionStrategy then the method signatures have been modified and are described below in the breaking changes section.

#577
New TracingInstrumentation has been added that tracks how long each field takes to execute. This is reported back on the ExecutionResult extensions field and gives you insight into how you graphql-java server is performing.

This tracing support follows the proposed Apollo Tracing specification https://github.com/apollographql/apollo-tracing which can then be viewed via their Optics performance monitoring tooling : https://www.apollodata.com/optics/

#641
You can now control the visibility of selected fields in the schema. A GraphqlFieldVisibility implementation can be attached to a schema that decide on what fields will be made visible to queries and introspection. This allows you to say restrict the view of the schema for different classes of users say.

#625
java.util.Optional is now supported as a return value from data fetchers and will be collapsed into either an object or the null value in graphql terms.

#618 #575 #560
Instrumentation was enhanced significantly to with an extra method when an ExecutionStrategy is entered and exited. It also allows you to intercept DataFetchers and results and hence inject new behaviour into the running system.

#616
The error messages for argument validation have been improved and better tells you went wrong and in more detail.

#650
You can now store extra meta data on GraphqlError objects that can be sent back to your client code

#552
The ExecutionResult object now has a toSpecification() method that gives you back and object that 100% complies with the graphql specification.

#449
There is now "path" support when running queries. Errors contain the path to which field was in error in a structured specified by the graphql specification and DataFetchers also get this path information.

#467 #470 #468
Schema IDL has been improved. Any additional types defined in schema IDL are now included into the build GraphqSchema object as expected, deprecation is now supported via IDL files and the build runtime type objects contain the original AST definitions.

List of breaking changes:

#593:

• The Instrumentation callback is now one method (with two parameters) instead of two methods.

#590 #380 #542 #487:

• ExecutionStrategy has been refactored by several PRs but it affects only custom strategies.
  Main changes are cleaned up parameters and support of CompletableFuture.

#550:

• ExecutionStrategy.handleDataFetchingException is removed: Instead a delegate DataFetcherExceptionHandler is used to handle Exceptions.

#211 #456 :

• An explicit root Object is added which is available to DataFetchers and is the source for the first level DataFetcher. Before that context was used for that purpose. Note: GraphQL.execute(String query, Object context) is still compatible to avoid unexpected bugs.

• The arguments objects for the Instrumentation are renamed to make them more clear: E.g. DataFetchParameters -> InstrumentationDataFetchParameters

#455:

• The overall scalar error logic was changed a bit. See this PR for details.

#427:

• By supporting the null literal the result of not providing an argument to a field was changed: not providing an arguments results in a arguments Map (for the DataFetcher) with no key in it and providing the null literal results in a Java null values.

#660:

• removes the deprecated methods for the Relay support.

Full List of changes:

See here for the full list of all changes.