Add override of Iterable#forEach to ensure that the cursor is always closed

JAVA-3630

Author: jyemin

driver-sync/src/main/com/mongodb/client/internal/MongoIterableImpl.java

@@ -16,7 +16,6 @@
 
 package com.mongodb.client.internal;
 
-import com.mongodb.Block;
 import com.mongodb.Function;
 import com.mongodb.ReadConcern;
 import com.mongodb.ReadPreference;
@@ -28,6 +27,7 @@
 import com.mongodb.lang.Nullable;
 
 import java.util.Collection;
+import java.util.function.Consumer;
 
 import static com.mongodb.assertions.Assertions.notNull;
 
@@ -116,26 +116,18 @@ public <U> MongoIterable<U> map(final Function<TResult, U> mapper) {
         return new MappingIterable<TResult, U>(this, mapper);
     }
 
-    @SuppressWarnings("overloads")
-    private void forEach(final Block<? super TResult> block) {
-        MongoCursor<TResult> cursor = iterator();
-        try {
+    @Override
+    public void forEach(final Consumer<? super TResult> action) {
+        try (MongoCursor<TResult> cursor = iterator()) {
             while (cursor.hasNext()) {
-                block.apply(cursor.next());
+                action.accept(cursor.next());
             }
-        } finally {
-            cursor.close();
         }
     }
 
     @Override
     public <A extends Collection<? super TResult>> A into(final A target) {
-        forEach(new Block<TResult>() {
-            @Override
-            public void apply(final TResult t) {
-                target.add(t);
-            }
-        });
+        forEach(target::add);
         return target;
     }
 

driver-sync/src/test/unit/com/mongodb/client/internal/FindIterableSpecification.groovy

@@ -19,6 +19,7 @@ package com.mongodb.client.internal
 
 import com.mongodb.CursorType
 import com.mongodb.Function
+import com.mongodb.MongoException
 import com.mongodb.MongoNamespace
 import com.mongodb.ReadConcern
 import com.mongodb.client.ClientSession
@@ -300,4 +301,28 @@ class FindIterableSpecification extends Specification {
         then:
         mongoIterable.getBatchSize() == batchSize
     }
+
+    // Really testing MongoIterableImpl#forEach, but doing it once here since that class is abstract
+    def 'forEach should close cursor when there is an exception during iteration'() {
+        given:
+        def cursor = Mock(BatchCursor) {
+            hasNext() >> {
+                throw new MongoException('');
+            }
+        }
+        def executor = new TestOperationExecutor([cursor])
+        def mongoIterable = new FindIterableImpl(null, namespace, Document, Document, codecRegistry, readPreference, readConcern,
+                executor, new Document())
+
+        when:
+        mongoIterable.forEach(new Consumer<Document>() {
+            @Override
+            void accept(Document document) {
+            }
+        })
+
+        then:
+        thrown(MongoException)
+        1 * cursor.close()
+    }
 }