Merge pull request #800 from google/nullsafe_regression_bugfix

Fixed a regression in Gson 2.6 where Gson caused NPE if the TypeAdapt…

gson/src/main/java/com/google/gson/internal/bind/JsonAdapterAnnotationTypeAdapterFactory.java

@@ -51,7 +51,7 @@ public final class JsonAdapterAnnotationTypeAdapterFactory implements TypeAdapte
   static TypeAdapter<?> getTypeAdapter(ConstructorConstructor constructorConstructor, Gson gson,
       TypeToken<?> fieldType, JsonAdapter annotation) {
     Class<?> value = annotation.value();
-    final TypeAdapter<?> typeAdapter;
+    TypeAdapter<?> typeAdapter;
     if (TypeAdapter.class.isAssignableFrom(value)) {
       Class<TypeAdapter<?>> typeAdapterClass = (Class<TypeAdapter<?>>) value;
       typeAdapter = constructorConstructor.get(TypeToken.get(typeAdapterClass)).construct();
@@ -64,7 +64,9 @@ public final class JsonAdapterAnnotationTypeAdapterFactory implements TypeAdapte
       throw new IllegalArgumentException(
           "@JsonAdapter value must be TypeAdapter or TypeAdapterFactory reference.");
     }
-
-    return typeAdapter.nullSafe();
+    if (typeAdapter != null) {
+      typeAdapter = typeAdapter.nullSafe();
+    }
+    return typeAdapter;
   }
 }

gson/src/test/java/com/google/gson/regression/JsonAdapterNullSafeTest.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2016 Google Inc.
+ *
+ * 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
+ * limitations under the License.
+ */
+package com.google.gson.regression;
+
+import com.google.gson.Gson;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.annotations.JsonAdapter;
+import com.google.gson.reflect.TypeToken;
+
+import junit.framework.TestCase;
+
+public class JsonAdapterNullSafeTest extends TestCase {
+  private final Gson gson = new Gson();
+
+  public void testNullSafeBugSerialize() throws Exception {
+    Device device = new Device("ec57803e");
+    gson.toJson(device);
+  }
+
+  public void testNullSafeBugDeserialize() throws Exception {
+    Device device = gson.fromJson("{'id':'ec57803e2'}", Device.class);
+    assertEquals("ec57803e2", device.id);
+  }
+
+  @JsonAdapter(Device.JsonAdapterFactory.class)
+  private static final class Device {
+    String id;
+    Device(String id) {
+      this.id = id;
+    }
+
+    static final class JsonAdapterFactory implements TypeAdapterFactory {
+      // The recursiveCall in {@link Device.JsonAdapterFactory} is the source of this bug
+      // because we use it to return a null type adapter on a recursive call.
+      private static final ThreadLocal<Boolean> recursiveCall = new ThreadLocal<Boolean>();
+
+      @SuppressWarnings({"unchecked", "rawtypes"})
+      @Override public <T> TypeAdapter<T> create(final Gson gson, TypeToken<T> type) {
+        if (type.getRawType() != Device.class || recursiveCall.get() != null) {
+          recursiveCall.set(null); // clear for subsequent use
+          return null;
+        }
+        recursiveCall.set(Boolean.TRUE);
+        return (TypeAdapter) gson.getDelegateAdapter(this, type);
+      }
+    }
+  }
+}