sdk/android/native_api/jni/class_loader.cc

/*
 *  Copyright 2017 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "sdk/android/native_api/jni/class_loader.h"

#include <algorithm>
#include <string>

#include "rtc_base/checks.h"
#include "sdk/android/generated_native_api_jni/WebRtcClassLoader_jni.h"
#include "sdk/android/native_api/jni/java_types.h"
#include "third_party/jni_zero/jni_zero.h"

// Abort the process if `jni` has a Java exception pending. This macros uses the
// comma operator to execute ExceptionDescribe and ExceptionClear ignoring their
// return values and sending "" to the error stream.
#define CHECK_EXCEPTION(jni)        \
  RTC_CHECK(!jni->ExceptionCheck()) \
      << (jni->ExceptionDescribe(), jni->ExceptionClear(), "")

namespace webrtc {

namespace {

class ClassLoader {
 public:
  explicit ClassLoader(JNIEnv* env)
      : class_loader_(jni::Java_WebRtcClassLoader_getClassLoader(env)) {
    class_loader_class_ = reinterpret_cast<jclass>(
        env->NewGlobalRef(env->FindClass("java/lang/ClassLoader")));
    CHECK_EXCEPTION(env);
    load_class_method_ =
        env->GetMethodID(class_loader_class_, "loadClass",
                         "(Ljava/lang/String;)Ljava/lang/Class;");
    CHECK_EXCEPTION(env);
  }

  ScopedJavaLocalRef<jclass> FindClass(JNIEnv* env, const char* c_name) {
    // ClassLoader.loadClass expects a classname with components separated by
    // dots instead of the slashes that JNIEnv::FindClass expects.
    std::string name(c_name);
    std::replace(name.begin(), name.end(), '/', '.');
    ScopedJavaLocalRef<jstring> j_name = NativeToJavaString(env, name);
    const jclass clazz = static_cast<jclass>(env->CallObjectMethod(
        class_loader_.obj(), load_class_method_, j_name.obj()));
    CHECK_EXCEPTION(env);
    return ScopedJavaLocalRef<jclass>(env, clazz);
  }

 private:
  ScopedJavaGlobalRef<jobject> class_loader_;
  jclass class_loader_class_;
  jmethodID load_class_method_;
};

static ClassLoader* g_class_loader = nullptr;

jclass GetClass(JNIEnv* env, const char* class_name, const char* unused) {
  RTC_CHECK(g_class_loader);
  return static_cast<jclass>(
      g_class_loader->FindClass(env, class_name).Release());
}

}  // namespace

void InitClassLoader(JNIEnv* env) {
  RTC_CHECK(g_class_loader == nullptr);
  g_class_loader = new ClassLoader(env);
  jni_zero::SetClassResolver(&GetClass);
}

ScopedJavaLocalRef<jclass> GetClass(JNIEnv* env, const char* c_name) {
  if (g_class_loader != nullptr) {
    // The class loader will be null in the JNI code called from the ClassLoader
    // ctor when we are bootstrapping ourself.
    return g_class_loader->FindClass(env, c_name);
  }
  // jni_zero generated code uses dots instead of slashes.
  // Convert to use slashes since that's what JNI's FindClass expects.
  // See
  // https://cs.android.com/android/platform/superproject/main/+/main:art/runtime/jni/check_jni.cc;l=349;drc=0f62043c1670cd365aba1894ad8046cdfc1c905d

  std::string name(c_name);
  std::replace(name.begin(), name.end(), '.', '/');
  return ScopedJavaLocalRef<jclass>(env, env->FindClass(name.c_str()));
}

}  // namespace webrtc