RegisterNatives JNI example

libregisternatives.cpp

#include <jni.h>

#include <iostream>
#include <string>

using namespace std;

extern "C"
JNIEXPORT void JNICALL sayHello(JNIEnv *env, jclass cls, jstring arg)
{
	const char *raw = env->GetStringUTFChars(arg, NULL);
	string s(raw);
	env->ReleaseStringUTFChars(arg, raw);
	cout << "Hello, " << s << endl;
}

static JNINativeMethod methods[] = {
	{ const_cast<char *>("sayHello"), const_cast<char *>("(Ljava/lang/String;)V"), reinterpret_cast<void *>(&sayHello) },
};

extern "C"
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *pvt)
{
	JNIEnv *env = NULL;

	if (vm->GetEnv((void **)&env, JNI_VERSION_1_2) != JNI_OK) {
		throw "Cannot get Java env";
	}

	jclass cls = env->FindClass("RegisterNativesExample");
	if (!cls)
		env->FatalError("Cannot file RegisterNativesExample class");

	env->RegisterNatives(cls, methods, 1);

	return JNI_VERSION_1_2;
}

Makefile

JAVA_HOME = /usr/lib/jvm/java-7-openjdk

CXXFLAGS += -Wall
CXXFLAGS += -I. -I$(JAVA_HOME)/include -I$(JAVA_HOME)/include/linux

all: libregisternatives.so RegisterNativesExample.class

clean:
	rm RegisterNativesExample.class libregisternatives.so

libregisternatives.o: libregisternatives.cpp
libregisternatives.so: libregisternatives.o
RegisterNativesExample.class: RegisterNativesExample.java

%.o: %.cpp
	$(CXX) $(CXXFLAGS) $(LDFLAGS) -fPIC -c $< 

%.so: %.o
	$(CXX) $(CXXFLAGS) $(LDFLAGS) -shared -o $@ $< 


%.class: %.java
	javac $<

%.h: %.class
	javah -cp . $(<:.class=)

RegisterNativesExample.java

public class RegisterNativesExample {

	static {
		System.loadLibrary("registernatives");
	}

	static native void sayHello(String args);

	static public void main(String[] args) {
		sayHello("World");
	}
}