Add a helper class for making asynchronous data fetchers (#798)

* Ignore files generated by Eclipse

* Add a helper class for making asynchronous data fetchers

* Add the ability to set the executor an async data fetcher will run in

* Reinstate original documentation and add further section for new method

* Make the fields of AsynchronousDataFetcher final

.gitignore

@@ -8,4 +8,8 @@ classes
 _site
 generated-src/
 out
-docs/_build/
+docs/_build/
+/bin/
+\.classpath
+\.project
+\.settings/

docs/execution.rst

@@ -345,6 +345,14 @@ The code above is written in long form.  With Java 8 lambdas it can be written m
 The graphql-java engine ensures that all the ``CompletableFuture`` objects are composed together to provide an execution result
 that follows the graphql specification.
 
+There is a helpful shortcut in graphql-java to create asynchronous data fetchers. 
+Use ``graphql.schema.AsynchronousDataFetcher.async(DataFetcher<T>)`` to wrap a 
+``DataFetcher``. This can be used with static imports to produce more readable code.
+
+.. code-block:: java
+
+        DataFetcher userDataFetcher = async(environment -> fetchUserViaHttp(environment.getArgument("userId")));
+
 Execution Strategies
 --------------------
 

src/main/java/graphql/schema/AsynchronousDataFetcher.java

@@ -0,0 +1,69 @@
+package graphql.schema;
+
+import static graphql.Assert.assertNotNull;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ForkJoinPool;
+
+import graphql.PublicApi;
+
+/**
+ * A modifier type that indicates the underlying data fetcher is run asynchronously
+ */
+@PublicApi
+public class AsynchronousDataFetcher<T> implements DataFetcher<CompletableFuture<T>> {
+
+    /**
+     * A factory method for creating asynchronous data fetchers so that when used with 
+     * static imports allows more readable code such as:
+     * <p>
+     * {@code .dataFetcher(async(fooDataFetcher))}
+     * <p>
+     * By default this will run in the {@link ForkJoinPool#commonPool()}. You can set 
+     * your own {@link Executor} with {@link #asyncWithExecutor(DataFetcher, Executor)}
+     *
+     * @param wrappedDataFetcher the data fetcher to run asynchronously
+     *
+     * @return a {@link DataFetcher} that will run the wrappedDataFetcher asynchronously
+     */
+    public static <T> AsynchronousDataFetcher<T> async(DataFetcher<T> wrappedDataFetcher) {
+        return new AsynchronousDataFetcher<>(wrappedDataFetcher);
+    }
+
+    /**
+     * A factory method for creating asynchronous data fetchers and setting the 
+     * {@link Executor} they run in so that when used with static imports allows 
+     * more readable code such as:
+     * <p>
+     * {@code .dataFetcher(asyncWithExecutor(fooDataFetcher, fooPool))}
+     *
+     * @param wrappedDataFetcher the data fetcher to run asynchronously
+     * @param executor to run the asynchronous data fetcher in
+     *
+     * @return a {@link DataFetcher} that will run the wrappedDataFetcher asynchronously in 
+     * the given {@link Executor}
+     */
+    public static <T> AsynchronousDataFetcher<T> asyncWithExecutor(DataFetcher<T> wrappedDataFetcher,
+            Executor executor) {
+        return new AsynchronousDataFetcher<>(wrappedDataFetcher, executor);
+    }
+
+    private final DataFetcher<T> wrappedDataFetcher;
+    private final Executor executor;
+
+    public AsynchronousDataFetcher(DataFetcher<T> wrappedDataFetcher) {
+        this(wrappedDataFetcher, ForkJoinPool.commonPool());
+    }
+
+    public AsynchronousDataFetcher(DataFetcher<T> wrappedDataFetcher, Executor executor) {
+        this.wrappedDataFetcher = assertNotNull(wrappedDataFetcher, "wrappedDataFetcher can't be null");
+        this.executor = assertNotNull(executor, "executor can't be null");
+    }
+
+    @Override
+    public CompletableFuture<T> get(DataFetchingEnvironment environment) {
+        return CompletableFuture.supplyAsync(() -> wrappedDataFetcher.get(environment), executor);
+    }
+
+}

src/test/groovy/graphql/schema/AsynchronousDataFetcherTest.groovy

@@ -0,0 +1,32 @@
+package graphql.schema
+
+import graphql.GraphQL
+import graphql.StarWarsData
+import graphql.TestUtil
+import graphql.execution.FieldCollector
+import graphql.language.AstPrinter
+import graphql.language.Field
+import graphql.schema.idl.MapEnumValuesProvider
+import graphql.schema.idl.RuntimeWiring
+import spock.lang.Specification
+
+import java.util.concurrent.CompletableFuture
+import java.util.stream.Collectors
+
+import static graphql.schema.idl.TypeRuntimeWiring.newTypeWiring
+
+
+class AsynchronousDataFetcherTest extends Specification {
+
+    def "A data fetcher can be made asynchronous with AsynchronousDataFetcher#async"() {
+        given:
+        DataFetchingEnvironment environment = Mock(DataFetchingEnvironment)
+
+        when:
+        DataFetcher asyncDataFetcher = AsynchronousDataFetcher.async({ env -> "value" })
+
+        then:
+        asyncDataFetcher.get(environment) instanceof CompletableFuture
+        asyncDataFetcher.get(environment).get() == "value"
+    }
+}