android: add LogListener

A Java object to send logs on the android side.

src/android/LogListener.cxx

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "LogListener.hxx"
+#include "java/Class.hxx"
+#include "java/String.hxx"
+#include "util/AllocatedString.hxx"
+#include "util/FormatString.hxx"
+
+void
+LogListener::OnLog(JNIEnv *env, int priority, const char *fmt, ...) const
+{
+	assert(env != nullptr);
+
+	Java::Class cls(env, env->GetObjectClass(Get()));
+
+	jmethodID method = env->GetMethodID(cls, "onLog",
+					    "(ILjava/lang/String;)V");
+
+	assert(method);
+
+	va_list args;
+	va_start(args, fmt);
+	const auto log = FormatStringV(fmt, args);
+	va_end(args);
+
+	env->CallVoidMethod(Get(), method, priority,
+			    Java::String(env, log.c_str()).Get());
+}