Issue #39: Should use DataFetcher specialized constructor (#44)

* Should use Datafeetcher specialized constructor

DataFetchers can now be instantiated using specialized constructors that accept strings for arguments.
This faciliates DataFetcher reusability for given fields (no need to create inumerous specific types).

Issue #39

* Introduce missing license header

Added mising license header.

Issue #39

Author: bmsantos

src/main/java/graphql/annotations/GraphQLAnnotations.java

@@ -62,6 +62,9 @@
 import static graphql.schema.GraphQLInterfaceType.newInterface;
 import static graphql.schema.GraphQLObjectType.newObject;
 import static graphql.schema.GraphQLUnionType.newUnionType;
+import static java.util.Arrays.stream;
+import static java.util.Objects.isNull;
+import static java.util.Objects.nonNull;
 
 /**
  * A utility class for extracting GraphQL data structures from annotated
@@ -321,7 +324,19 @@ protected GraphQLFieldDefinition getField(Field field) throws GraphQLAnnotations
         }
 
         GraphQLDataFetcher dataFetcher = field.getAnnotation(GraphQLDataFetcher.class);
-        DataFetcher actualDataFetcher = dataFetcher != null ? newInstance(dataFetcher.value()) : null;
+        DataFetcher actualDataFetcher = null;
+        if (nonNull(dataFetcher)) {
+            final String[] args = dataFetcher.args();
+            if (args.length == 0) {
+                actualDataFetcher = newInstance(dataFetcher.value());
+            } else {
+                try {
+                    final Constructor<? extends DataFetcher> ctr = dataFetcher.value().getDeclaredConstructor(
+                      stream(args).map(v -> String.class).toArray(Class[]::new));
+                    actualDataFetcher = constructNewInstance(ctr, (Object[]) args);
+                } catch (final NoSuchMethodException e) {}
+            }
+        }
 
         if (actualDataFetcher == null) {
 

src/main/java/graphql/annotations/GraphQLDataFetcher.java

@@ -25,4 +25,5 @@
 @Retention(RetentionPolicy.RUNTIME)
 public @interface GraphQLDataFetcher {
     Class<? extends DataFetcher> value();
+    String[] args() default {};
 }

src/test/java/graphql/annotations/GraphQLDataFetcherTest.java

@@ -0,0 +1,83 @@
+/**
+ * Copyright 2016 Yurii Rashkovskii
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ */
+package graphql.annotations;
+
+import java.util.HashMap;
+
+import graphql.ExecutionResult;
+import graphql.GraphQL;
+import graphql.schema.DataFetcher;
+import graphql.schema.DataFetchingEnvironment;
+import graphql.schema.GraphQLObjectType;
+import graphql.schema.GraphQLSchema;
+import graphql.schema.PropertyDataFetcher;
+import org.testng.annotations.Test;
+
+import static graphql.schema.GraphQLSchema.newSchema;
+import static org.testng.Assert.assertNotNull;
+import static org.testng.Assert.assertTrue;
+
+public class GraphQLDataFetcherTest {
+
+  @Test
+  public void shouldUsePreferredConstructor() {
+    // Given
+    final GraphQLObjectType object = GraphQLAnnotations.object(GraphQLDataFetcherTest.TestGraphQLQuery.class);
+    final GraphQLSchema schema = newSchema().query(object).build();
+    final GraphQL graphql = new GraphQL(schema);
+
+    // When
+    final ExecutionResult result = graphql.execute("{sample {isGreat}}");
+
+    // Then
+    final HashMap<String, Object> data = (HashMap) result.getData();
+    assertNotNull(data);
+    assertTrue(((HashMap<String,Boolean>)data.get("sample")).get("isGreat"));
+  }
+
+  @GraphQLName("Query")
+  public static class TestGraphQLQuery {
+    @GraphQLField
+    @GraphQLDataFetcher(SampleDataFetcher.class)
+    public TestSample sample() { // Note that GraphQL uses TestSample to build the graph
+      return null;
+    }
+  }
+
+  public static class TestSample {
+    @GraphQLField
+    @GraphQLDataFetcher(value = PropertyDataFetcher.class, args = "isGreat")
+    private Boolean isGreat = false; // Defaults to FieldDataFetcher
+  }
+
+  public static class SampleDataFetcher implements DataFetcher {
+    @Override
+    public Object get(final DataFetchingEnvironment environment) {
+      return new Sample(); // Notice that it return a Sample, not a TestSample
+    }
+  }
+
+  public static class Sample {
+    private Boolean isGreat = true;
+
+    public Boolean getIsGreat() {
+      return isGreat;
+    }
+
+    public void setIsGreat(final Boolean isGreat) {
+      this.isGreat = isGreat;
+    }
+  }
+}