Java如何调用C/C++(JNI)
Java如何调用C/C++(JNI)
Java开发者 jdeveloper
1. program Java source file loading Native method
//
//
// NativeDemo
// Author: huang_jc 1999/05/20
// file name: NativeDemo.java
public class NativeDemo
{
int i;
int j;
public static void main(String args[])
{
NativeDemo ob = new NativeDemo();
ob.i = 10;
ob.j = ob.test();
System.out.println("this is ob.i:"+ob.i+"
");
System.out.println("this is ob.j:"+ob.j);
}
public native int test();
static
{
System.loadLibrary("NativeDemo");
}
}
2.Compile file NativeDemo.java
Javac NativeDemo.java
3.Use javah.exe to prodUCe file NativeDemo.c and NativeDemo.h
a : javah NativeDemo to produce NativeDemo.h which is:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <native.h>
/* Header for class NativeDemo */
#ifndef _Included_NativeDemo
#define _Included_NativeDemo
#pragma pack(4)
typedef struct ClassNativeDemo {
long i;
long j;
} ClassNativeDemo;
HandleTo(NativeDemo);
#pragma pack()
#ifdef __cplusplus
extern "C" {
#endif
extern long NativeDemo_test(struct HNativeDemo *);
#ifdef __cplusplus
}
#endif
#endif
b : use javah -stubs NativeDemo to produce NativeDemo.c which seems as:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <StubPreamble.h>
/* Stubs for class NativeDemo */
/* SYMBOL: "NativeDemo/test()I", Java_NativeDemo_test_stub */
__declspec(dlleXPort) stack_item *Java_NativeDemo_test_stub(stack_item *_P_,struct execenv *_EE_) {
extern long NativeDemo_test(void *);
_P_[0].i = NativeDemo_test(_P_[0].p);
return _P_ + 1;
}
4. Write your own implimentation of method test()
//file name test.c
#include <StubPreamble.h>
#include "nativedemo.h"
#include <stdio.h>
long NativeDemo_test(HNativeDemo *this)
{
printf("hello:!
");
printf("this is in the native method!
");
return (unhand(this)->i)*2;
}
5. link NativeDemo.c and test.c to produce NativeDemo.dll
Use VC++5.0 tools :Cl.exe
Cl /GD NativeDemo.c test.c /LD
then we get NativeDemo.dll
NativeDemo.c
test.c
Generating Code...
/out:NativeDemo.dll
/dll
/implib:NativeDemo.lib
NativeDemo.obj
test.obj
Creating library NativeDemo.lib and object NativeDemo.ex
Press any key to continue
6.Run
java NativeDemo
we get the such result:
D:vj11user
ative>java NativeDemo
hello:!
this is in the native method!
this is ob.i:10
this is ob.j:20
D:vj11user
ative>
NOTE:
Do not forget this:
c:> set INCLUDE=d:javainclude;d:javawin32;%INCLUDE%
C:>set LIB =d:javalib;%LIB%
where d:java is the Directory of your jdk
new version jdk1.2.1 :
With new jdk1.2.1 :
1.javac NativeDemo.java
2. javah NativeDemo to produce head file (You need not to javah -stubs NativeDemo to produce NativeDemo.c file),
You don`t need the c file. Just the NativeDemo.h is sufficient!
3.Use VC++ produce a window dll project and add the NativeDemo.h to it.
then implement the function. All is OK!
NOTE: the data type conversion between java and c++.See jni.h for more information.