Android/Context: look up methods once during startup

src/Main.cxx

@@ -614,9 +614,12 @@ Java_org_musicpd_Bridge_run(JNIEnv *env, jclass, jobject _context, jobject _logL
 	Java::Init(env);
 	Java::Object::Initialise(env);
 	Java::File::Initialise(env);
+
 	Environment::Initialise(env);
 	AtScopeExit(env) { Environment::Deinitialise(env); };
 
+	Context::Initialise(env);
+
 	context = new Context(env, _context);
 	AtScopeExit() { delete context; };
 

src/android/Context.cxx

@@ -26,19 +26,31 @@
 
 #include "AudioManager.hxx"
 
+static jmethodID getExternalFilesDir_method,
+  getCacheDir_method,
+  getSystemService_method;
+
+void
+Context::Initialise(JNIEnv *env) noexcept
+{
+	Java::Class cls{env, "android/content/Context"};
+
+	getExternalFilesDir_method = env->GetMethodID(cls, "getExternalFilesDir",
+						      "(Ljava/lang/String;)Ljava/io/File;");
+	getCacheDir_method = env->GetMethodID(cls, "getCacheDir",
+					      "()Ljava/io/File;");
+	getSystemService_method = env->GetMethodID(cls, "getSystemService",
+						   "(Ljava/lang/String;)Ljava/lang/Object;");
+}
+
 AllocatedPath
 Context::GetExternalFilesDir(JNIEnv *env, const char *_type) noexcept
 {
 	assert(_type != nullptr);
 
-	Java::Class cls{env, env->GetObjectClass(Get())};
-	jmethodID method = env->GetMethodID(cls, "getExternalFilesDir",
-					    "(Ljava/lang/String;)Ljava/io/File;");
-	assert(method);
-
 	Java::String type{env, _type};
 
-	jobject file = env->CallObjectMethod(Get(), method, type.Get());
+	jobject file = env->CallObjectMethod(Get(), getExternalFilesDir_method, type.Get());
 	if (Java::DiscardException(env) || file == nullptr)
 		return nullptr;
 
@@ -50,12 +62,7 @@ Context::GetCacheDir(JNIEnv *env) const noexcept
 {
 	assert(env != nullptr);
 
-	Java::Class cls(env, env->GetObjectClass(Get()));
-	jmethodID method = env->GetMethodID(cls, "getCacheDir",
-					    "()Ljava/io/File;");
-	assert(method);
-
-	jobject file = env->CallObjectMethod(Get(), method);
+	jobject file = env->CallObjectMethod(Get(), getCacheDir_method);
 	if (Java::DiscardException(env) || file == nullptr)
 		return nullptr;
 
@@ -67,13 +74,8 @@ Context::GetAudioManager(JNIEnv *env) noexcept
 {
 	assert(env != nullptr);
 
-	Java::Class cls(env, env->GetObjectClass(Get()));
-	jmethodID method = env->GetMethodID(cls, "getSystemService",
-					    "(Ljava/lang/String;)Ljava/lang/Object;");
-	assert(method);
-
 	Java::String name(env, "audio");
-	jobject am = env->CallObjectMethod(Get(), method, name.Get());
+	jobject am = env->CallObjectMethod(Get(), getSystemService_method, name.Get());
 	if (Java::DiscardException(env) || am == nullptr)
 		return nullptr;
 

src/android/Context.hxx

@@ -27,6 +27,12 @@ class AudioManager;
 
 class Context : public Java::GlobalObject {
 public:
+	/**
+	 * Global initialisation.  Looks up the methods of the
+	 * Context Java class.
+	 */
+	static void Initialise(JNIEnv *env) noexcept;
+
 	Context(JNIEnv *env, jobject obj) noexcept
 		:Java::GlobalObject(env, obj) {}