Download Java Native Interface Tutorial

Java Native Interface
Tutorial
Xiaolin Li
Rutgers
2/20/2004
Rutgers University Excellence Campaign
Motivation
• A seamless bridge between Java and
native implementation in C, C++ or other
languages
Java Application
and Library
Native Application
And Library
JVM
JNI
Host Environment
(OS)
Rutgers University Excellence Campaign
2
Getting Started
1. Create a Java
class that declares
the native method
Hello.h
4. Write C impl
5. Compile C code
and generate
native lib
Hello.java
3. Javah –jni
Hello
Hello.c
2. Compile
(javac)
Hello.class
6. Done
Run the java
application
Java Hello
Hello.dll
or libhello.so
Rutgers University Excellence Campaign
3
Hello World
// Hello.java
public class Hello {
static {
String libpath =
System.getProperty("java.library.path");
libpath += ":.";
System.setProperty("java.library.path", libpath);
System.loadLibrary("Hello");
}
public static void main(String[] args) {
Hello hello = new Hello();
hello.Hello();
}
private native void Hello();
}
Rutgers University Excellence Campaign
4
Hello World
// Hello.c
#include <stdio.h>
#include <math.h>
#include "Hello.h"
JNIEXPORT void JNICALL Java_Hello_hello(JNIEnv*
env, jobject obj)
{
printf("Hello, World.\n");
}
Rutgers University Excellence Campaign
5
Executable Java Application
int main(int argc, char * argv[])
{
JNIEnv *env;
JavaVM *jvm;
jint res;
jclass cls;
jmethodID mid;
// 1. create JVM
res = JNI_CreateJavaVM(&jvm, (void**) &env, &vm_args);
// 2. find and load the Java application
cls = (*env)->FindClass(env, "Hello");
mid = (*env)->GetStaticMethodID(env, cls, "main",
"([Ljava/lang/String;)V");
// 3. execute it
(*env)->CallStaticVoidMethod(env, cls, mid, args);
(*jvm)->DestroyJavaVM(jvm);
}
Rutgers University Excellence Campaign
6
Thank You
2/20/2004
Rutgers University Excellence Campaign