Add AutoJObject and AutoGlobalJObject

base/android/scoped_java_reference.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_ANDROID_SCOPED_JAVA_REFERENCE_H_
+#define BASE_ANDROID_SCOPED_JAVA_REFERENCE_H_
+
+#include <jni.h>
+#include <stddef.h>
+
+namespace base {
+namespace android {
+
+// Holds a local reference to a Java object. The local reference is scoped
+// to the lifetime of this object. Note that since a JNI Env is only suitable
+// for use on a single thread, objects of this class must be created, used and
+// destroyed on the same thread.
+template<typename T>
+class ScopedJavaReference {
+ public:
+  // Holds a NULL reference.
+  ScopedJavaReference()
+      : env_(NULL),
+        obj_(NULL) {
+  }
+  // Assumes that obj is a local reference to a Java object and takes ownership
+  // of this local reference.
+  ScopedJavaReference(JNIEnv* env, T obj)
+      : env_(env),
+        obj_(obj) {
+  }
+  // Takes a new local reference to the Java object held by other.
+  ScopedJavaReference(const ScopedJavaReference& other)
+      : env_(other.env_),
+        obj_(other.obj_ ? static_cast<T>(other.env_->NewLocalRef(other.obj_)) :
+            NULL) {
+  }
+  ~ScopedJavaReference() {
+    if (obj_)
+      env_->DeleteLocalRef(obj_);
+  }
+
+  void operator=(const ScopedJavaReference& other) {
+    if (obj_)
+      env_->DeleteLocalRef(obj_);
+    env_ = other.env_;
+    obj_ = other.obj_ ? static_cast<T>(env_->NewLocalRef(other.obj_)) : NULL;
+  }
+
+  JNIEnv* env() const { return env_; }
+  T obj() const { return obj_; }
+
+  // Releases the local reference to the caller. The caller *must* delete the
+  // local reference when it is done with it.
+  T Release() {
+    jobject obj = obj_;
+    obj_ = NULL;
+    return obj;
+  }
+
+ private:
+  JNIEnv* env_;
+  T obj_;
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_SCOPED_JAVA_REFERENCE_H_