Fixed a regression in Gson 2.6 where Gson caused NPE if the TypeAdapterFactory.create() returned null.

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 +1,186 @@
+/*
+ * 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 java.io.IOException;
+import java.util.Objects;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParser;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSyntaxException;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.annotations.JsonAdapter;
+import com.google.gson.annotations.SerializedName;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonToken;
+import com.google.gson.stream.JsonWriter;
+
+import junit.framework.TestCase;
+
+public class JsonAdapterNullSafeTest extends TestCase {
+  private final Gson gson = new Gson();
+
+  /**
+   * The recursiveCall in {@link ControlData.JsonAdapterFactory} is the source of this bug
+   * because it returns a null type adapter.
+   */
+  public void testTypeAdapterFactoryNullSafeBug() throws IOException {
+      ControlData control = new ControlData("ec57803e", 2, true, 11211);
+      Device device = new Device("device1", control);
+      String json = gson.toJson(device);
+
+      json = "\"{\\\"id\\\":\\\"ec57803e2\\\",\\\"category\\\":2,\\\"alwaysOn\\\":true,\\\"codeset_id\\\":11211}\"";
+      control = gson.fromJson(json, ControlData.class);
+      assertEquals("ec57803e2", control.id);
+      assertTrue(control.alwaysOn);
+      assertEquals(11211, control.codesetId);
+      assertEquals(2, control.category);
+
+      String deviceJson = "{'id':'device1','controlData':null}";
+      device = gson.fromJson(deviceJson, Device.class);
+      assertNull(device.controlData);
+
+      deviceJson = "{'id':'device1','controlData':{'id':'ec57803e2','category':2,'alwaysOn':true,'codeset_id':12221}}";
+      device = gson.fromJson(deviceJson, Device.class);
+      assertEquals(12221, device.controlData.codesetId);
+
+      deviceJson = "{'id':'device1','controlData':'\\\"{}\\\"'}";
+      device = gson.fromJson(deviceJson, Device.class);
+
+      try {
+          deviceJson = "{'id':'device1','controlData':'a'}";
+          device = gson.fromJson(deviceJson, Device.class);
+          assertNotNull(device.controlData);
+          fail();
+      } catch (JsonSyntaxException expected) {}
+
+      deviceJson = "{'id':'device1','controlData':'  '}";
+      device = gson.fromJson(deviceJson, Device.class);
+      assertNull(device.controlData);
+  }
+
+  private static final class Device {
+    @SuppressWarnings("unused")
+    String id;
+    ControlData controlData;
+
+    public Device(String id, ControlData controlData) {
+      this.id = id;
+      this.controlData = controlData;
+    }
+  }
+
+  @JsonAdapter(ControlData.JsonAdapterFactory.class)
+  private static final class ControlData {
+    String id;
+    int category;
+    boolean alwaysOn;
+    @SerializedName("codeset_id") int codesetId;
+    ControlData(String id, int category, boolean alwaysOn, int codesetId) {
+      this.id = id;
+      this.category = category;
+      this.alwaysOn = alwaysOn;
+      this.codesetId = codesetId;
+    }
+
+    /**
+     * DeviceControlData is received as String in JSON instead of proper JSON.
+     * So, we need to write a special type adapter.
+     */
+    static final class JsonAdapterFactory extends StringifiedJsonAdapterFactory<ControlData> {
+      private static final ThreadLocal<Boolean> recursiveCall = new ThreadLocal<Boolean>();
+      public JsonAdapterFactory() {
+        super(recursiveCall, ControlData.class, true);
+      }
+    }
+  }
+
+  /**
+   * Converts an object to Stringified JSON for saving in a JSON field as a string type.
+   */
+  private static class StringifiedJsonAdapterFactory<R> implements TypeAdapterFactory {
+    private final Class<R> targetType;
+    private final ThreadLocal<Boolean> recursiveCall;
+    private final boolean writeAsJson;
+
+    /**
+     * @param recursiveCall provide a static ThreadLocal to workaround a Gson bug where
+     *   annotation-based type adapter factories can't be skipped over.
+     * @param targetType The class whose instances needs to be written in stringified form.
+     * @param writeAsJson Set this to true to write the output as JSON not string.
+     */
+    public StringifiedJsonAdapterFactory(ThreadLocal<Boolean> recursiveCall, Class<R> targetType,
+        boolean writeAsJson) {
+      this.recursiveCall = recursiveCall;
+      this.targetType = targetType;
+      this.writeAsJson = writeAsJson;
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Override public <T> TypeAdapter<T> create(final Gson gson, TypeToken<T> type) {
+      if (type.getRawType() != targetType || recursiveCall.get() != null) {
+        recursiveCall.set(null); // clear for subsequent use
+        return null;
+      }
+      recursiveCall.set(Boolean.TRUE);
+      final TypeAdapter<R> delegate = (TypeAdapter) gson.getDelegateAdapter(this, type);
+      return (TypeAdapter) new TypeAdapter<R>() {
+        @Override public void write(JsonWriter out, R value) throws IOException {
+          if (writeAsJson) {
+            delegate.write(out, value);
+          } else {
+            // delegate.toJson(value) will write nulls. avoid that by using gson.toJson()
+            String json = gson.toJson(delegate.toJsonTree(value));
+            out.value(json);
+          }
+        }
+        @Override public R read(JsonReader in) throws IOException {
+          JsonToken token = in.peek();
+          JsonElement root;
+          if (token == JsonToken.BEGIN_OBJECT) {
+            return delegate.read(in);
+          } else { // assume to be string
+            String json = in.nextString();
+            JsonParser parser = new JsonParser();
+            root = parseString(parser, json, null);
+            return root == null ? null : delegate.fromJsonTree(root);
+          }
+        }
+
+        private JsonElement parseString(JsonParser parser, String json, String prevJson)
+            throws IOException {
+          if (json == null || json.trim().isEmpty()) {
+            return null;
+          }
+          JsonElement root = parser.parse(json);
+          if (root instanceof JsonPrimitive) {
+            prevJson = json;
+            json = root.getAsString();
+            if (Objects.equals(json, prevJson)) {
+              throw new JsonSyntaxException("Unexpected Json: " + json);
+            }
+            return parseString(parser, json, prevJson);
+          }
+          return root;
+        }
+      }.nullSafe();
+    }
+  }
+}