java: new helper library for the Android port

10 files changed, 680 insertions, 0 deletions

diff --git a/src/java/Class.hxx b/src/java/Class.hxx
new file mode 100644
index 000000000..9496ee67d
--- /dev/null
+++ b/src/java/Class.hxx
@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_CLASS_HXX
+#define JAVA_CLASS_HXX
+
+#include "Ref.hxx"
+
+#include <assert.h>
+
+namespace Java {
+	/**
+	 * Wrapper for a local "jclass" reference.
+	 */
+	class Class : public Java::LocalRef<jclass> {
+	public:
+		Class(JNIEnv *env, jclass cls)
+			:LocalRef<jclass>(env, cls) {}
+
+		Class(JNIEnv *env, const char *name)
+			:LocalRef<jclass>(env, env->FindClass(name)) {}
+	};
+
+	/**
+	 * Wrapper for a global "jclass" reference.
+	 */
+	class TrivialClass : public TrivialRef<jclass> {
+	public:
+		void Find(JNIEnv *env, const char *name) {
+			assert(env != nullptr);
+			assert(name != nullptr);
+
+			jclass cls = env->FindClass(name);
+			assert(cls != nullptr);
+
+			Set(env, cls);
+			env->DeleteLocalRef(cls);
+		}
+
+		bool FindOptional(JNIEnv *env, const char *name) {
+			assert(env != nullptr);
+			assert(name != nullptr);
+
+			jclass cls = env->FindClass(name);
+			if (cls == nullptr) {
+				env->ExceptionClear();
+				return false;
+			}
+
+			Set(env, cls);
+			env->DeleteLocalRef(cls);
+			return true;
+		}
+	};
+}
+
+#endif
diff --git a/src/java/Exception.hxx b/src/java/Exception.hxx
new file mode 100644
index 000000000..adbdebb47
--- /dev/null
+++ b/src/java/Exception.hxx
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2010-2012 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_EXCEPTION_HXX
+#define JAVA_EXCEPTION_HXX
+
+#include <jni.h>
+
+namespace Java {
+	/**
+	 * Check if an exception has occurred, and discard it.
+	 *
+	 * @return true if an exception was found (and discarded)
+	 */
+	static inline bool DiscardException(JNIEnv *env) {
+		bool result = env->ExceptionCheck();
+		if (result)
+			env->ExceptionClear();
+		return result;
+	}
+}
+
+#endif
diff --git a/src/java/File.cxx b/src/java/File.cxx
new file mode 100644
index 000000000..03e3defdf
--- /dev/null
+++ b/src/java/File.cxx
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2010-2012 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "File.hxx"
+#include "Class.hxx"
+
+jmethodID Java::File::getAbsolutePath_method;
+
+void
+Java::File::Initialise(JNIEnv *env)
+{
+	Class cls(env, "java/io/File");
+
+	getAbsolutePath_method = env->GetMethodID(cls, "getAbsolutePath",
+						  "()Ljava/lang/String;");
+}
diff --git a/src/java/File.hxx b/src/java/File.hxx
new file mode 100644
index 000000000..57af6199c
--- /dev/null
+++ b/src/java/File.hxx
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2010-2012 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_FILE_HXX
+#define JAVA_FILE_HPP
+
+#include "Object.hxx"
+
+#include <jni.h>
+
+namespace Java {
+	/**
+	 * Wrapper for a java.io.File object.
+	 */
+	class File : public LocalObject {
+		static jmethodID getAbsolutePath_method;
+
+	public:
+		static void Initialise(JNIEnv *env);
+
+		static jstring getAbsolutePath(JNIEnv *env, jobject file) {
+			return (jstring)env->CallObjectMethod(file,
+							      getAbsolutePath_method);
+		}
+	};
+}
+
+#endif
diff --git a/src/java/Global.cxx b/src/java/Global.cxx
new file mode 100644
index 000000000..1d1160127
--- /dev/null
+++ b/src/java/Global.cxx
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Global.hxx"
+
+namespace Java {
+	JavaVM *jvm;
+
+	void Init(JNIEnv *env)
+	{
+		env->GetJavaVM(&jvm);
+	}
+}
diff --git a/src/java/Global.hxx b/src/java/Global.hxx
new file mode 100644
index 000000000..5fdf91daf
--- /dev/null
+++ b/src/java/Global.hxx
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_GLOBAL_HXX
+#define JAVA_GLOBAL_HXX
+
+#include "Compiler.h"
+
+#include <jni.h>
+
+namespace Java {
+	extern JavaVM *jvm;
+
+	void Init(JNIEnv *env);
+
+	static inline void
+	DetachCurrentThread()
+	{
+		if (jvm != nullptr)
+			jvm->DetachCurrentThread();
+	}
+
+	static inline gcc_pure
+	JNIEnv *GetEnv()
+	{
+		JNIEnv *env;
+		jvm->AttachCurrentThread(&env, nullptr);
+		return env;
+	}
+}
+
+#endif
diff --git a/src/java/Object.hxx b/src/java/Object.hxx
new file mode 100644
index 000000000..226ad7623
--- /dev/null
+++ b/src/java/Object.hxx
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_OBJECT_HXX
+#define JAVA_OBJECT_HXX
+
+#include "Ref.hxx"
+
+#include <jni.h>
+
+namespace Java {
+	/**
+	 * Wrapper for a local "jobject" reference.
+	 */
+	typedef LocalRef<jobject> LocalObject;
+
+	class Object : public GlobalRef<jobject> {
+	public:
+		/**
+		 * Constructs an uninitialized object.  The method
+		 * set() must be called before it is destructed.
+		 */
+		Object() = default;
+
+		Object(JNIEnv *env, jobject obj):GlobalRef<jobject>(env, obj) {}
+	};
+}
+
+#endif
diff --git a/src/java/Ref.hxx b/src/java/Ref.hxx
new file mode 100644
index 000000000..e9966f1c6
--- /dev/null
+++ b/src/java/Ref.hxx
@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_REF_HXX
+#define JAVA_REF_HXX
+
+#include "Global.hxx"
+
+#include <jni.h>
+
+#include <assert.h>
+
+namespace Java {
+	/**
+	 * Hold a local reference on a JNI object.
+	 */
+	template<typename T>
+	class LocalRef {
+		JNIEnv *const env;
+		const T value;
+
+	public:
+		/**
+		 * The local reference is obtained by the caller.
+		 */
+		LocalRef(JNIEnv *_env, T _value):env(_env), value(_value) {
+			assert(env != nullptr);
+			assert(value != nullptr);
+		}
+
+		~LocalRef() {
+			env->DeleteLocalRef(value);
+		}
+
+		LocalRef(const LocalRef &other) = delete;
+		LocalRef &operator=(const LocalRef &other) = delete;
+
+		T Get() const {
+			return value;
+		}
+
+		operator T() const {
+			return value;
+		}
+	};
+
+	/**
+	 * Hold a global reference on a JNI object.
+	 */
+	template<typename T>
+	class GlobalRef {
+		T value;
+
+	public:
+		/**
+		 * Constructs an uninitialized object.  The method set() must be
+		 * called before it is destructed.
+		 */
+		GlobalRef() = default;
+
+		GlobalRef(JNIEnv *env, T _value):value(_value) {
+			assert(env != nullptr);
+			assert(value != nullptr);
+
+			value = (T)env->NewGlobalRef(value);
+		}
+
+		~GlobalRef() {
+			GetEnv()->DeleteGlobalRef(value);
+		}
+
+		GlobalRef(const GlobalRef &other) = delete;
+		GlobalRef &operator=(const GlobalRef &other) = delete;
+
+		/**
+		 * Sets the object, ignoring the previous value.  This is only
+		 * allowed once after the default constructor was used.
+		 */
+		void Set(JNIEnv *env, T _value) {
+			assert(_value != nullptr);
+
+			value = (T)env->NewGlobalRef(_value);
+		}
+
+		T Get() const {
+			return value;
+		}
+
+		operator T() const {
+			return value;
+		}
+	};
+
+	/**
+	 * Container for a global reference to a JNI object that gets
+	 * initialised and deinitialised explicitly.  Since there is no
+	 * implicit initialisation in the default constructor, this is a
+	 * trivial C++ class.  It should only be used for global variables
+	 * that are implicitly initialised with zeroes.
+	 */
+	template<typename T>
+	class TrivialRef {
+		T value;
+
+	public:
+		constexpr TrivialRef() {};
+
+		TrivialRef(const TrivialRef &other) = delete;
+		TrivialRef &operator=(const TrivialRef &other) = delete;
+
+		bool IsDefined() const {
+			return value != nullptr;
+		}
+
+		/**
+		 * Obtain a global reference on the specified object and store it.
+		 * This object must not be set already.
+		 */
+		void Set(JNIEnv *env, T _value) {
+			assert(value == nullptr);
+			assert(_value != nullptr);
+
+			value = (T)env->NewGlobalRef(_value);
+		}
+
+		/**
+		 * Release the global reference and clear this object.
+		 */
+		void Clear(JNIEnv *env) {
+			assert(value != nullptr);
+
+			env->DeleteGlobalRef(value);
+			value = nullptr;
+		}
+
+		/**
+		 * Release the global reference and clear this object.  It is
+		 * allowed to call this method without ever calling Set().
+		 */
+		void ClearOptional(JNIEnv *env) {
+			if (value != nullptr)
+				Clear(env);
+		}
+
+		T Get() const {
+			return value;
+		}
+
+		operator T() const {
+			return value;
+		}
+	};
+}
+
+#endif
diff --git a/src/java/String.cxx b/src/java/String.cxx
new file mode 100644
index 000000000..8ffb82d72
--- /dev/null
+++ b/src/java/String.cxx
@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "String.hxx"
+#include "util/StringUtil.hxx"
+
+char *
+Java::String::CopyTo(JNIEnv *env, jstring value,
+		     char *buffer, size_t max_size)
+{
+	const char *p = env->GetStringUTFChars(value, nullptr);
+	if (p == nullptr)
+		return nullptr;
+
+	char *result = CopyString(buffer, p, max_size);
+	env->ReleaseStringUTFChars(value, p);
+	return result;
+}
diff --git a/src/java/String.hxx b/src/java/String.hxx
new file mode 100644
index 000000000..a58385f50
--- /dev/null
+++ b/src/java/String.hxx
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2010-2011 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef JAVA_STRING_HXX
+#define JAVA_STRING_HXX
+
+#include "Ref.hxx"
+
+#include <jni.h>
+
+#include <assert.h>
+#include <stddef.h>
+
+namespace Java {
+	/**
+	 * Wrapper for a local "jstring" reference.
+	 */
+	class String : public LocalRef<jstring> {
+	public:
+		String(JNIEnv *env, jstring value)
+			:LocalRef<jstring>(env, value) {}
+
+		String(JNIEnv *_env, const char *_value)
+			:LocalRef<jstring>(_env, _env->NewStringUTF(_value)) {}
+
+		/**
+		 * Copy the value to the specified buffer.  Truncates
+		 * the value if it does not fit into the buffer.
+		 *
+		 * @return a pointer to the terminating null byte,
+		 * nullptr on error
+		 */
+		static char *CopyTo(JNIEnv *env, jstring value,
+				    char *buffer, size_t max_size);
+
+		/**
+		 * Copy the value to the specified buffer.  Truncates
+		 * the value if it does not fit into the buffer.
+		 *
+		 * @return a pointer to the terminating null byte,
+		 * nullptr on error
+		 */
+		char *CopyTo(JNIEnv *env, char *buffer, size_t max_size) {
+			return CopyTo(env, Get(), buffer, max_size);
+		}
+	};
+}
+
+#endif