Java Native Interface Tutorial

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Java Native Interface Tutorial

• Xiaolin Li
• Rutgers

2
Motivation

• A seamless bridge between Java and native
  implementation in C, C or other languages

Java Application and Library
Native Application And Library
Host Environment (OS)
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Getting Started
1. Create a Java class that declares the native
method
2. Compile (javac)
Hello.java
3. Javah jni Hello
Hello.class
Hello.h
6. Done Run the java application Java Hello
Hello.c
4. Write C impl
5. Compile C code and generate native lib
Hello.dll or libhello.so
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Hello World

• // Hello.java
• public class Hello
• static
• String libpath
  System.getProperty("java.library.path")
• libpath "."
• System.setProperty("java.library.p
  ath", libpath)
• System.loadLibrary("Hello")
• public static void main(String args)
• Hello hello new Hello()
• hello.Hello()
• private native void Hello()

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Hello World

• // Hello.c
• include ltstdio.hgt
• include ltmath.hgt
• include "Hello.h"
• JNIEXPORT void JNICALL Java_Hello_hello(JNIEnv
  env, jobject obj)
• printf("Hello, World.\n")

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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)-gtFindClass(env, "Hello")
• mid (env)-gtGetStaticMethodID(env, cls,
  "main", "(Ljava/lang/String)V")
• // 3. execute it
• (env)-gtCallStaticVoidMethod(env, cls, mid,
  args)
• (jvm)-gtDestroyJavaVM(jvm)

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Thank You