java使用JNA(Java Native Access)調(diào)用dll的方法

2019-11-26 15:54:46

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JNA(Java Native Access)：建立在JNI之上的Java開(kāi)源框架，SUN主導(dǎo)開(kāi)發(fā)，用來(lái)調(diào)用C、C++代碼，尤其是底層庫(kù)文件（windows中叫dll文件，linux下是so【shared object】文件）。
JNI是Java調(diào)用原生函數(shù)的唯一機(jī)制，JNA就是建立在JNI之上，JNA簡(jiǎn)化了Java調(diào)用原生函數(shù)的過(guò)程。JNA提供了一個(gè)動(dòng)態(tài)的C語(yǔ)言編寫(xiě)的轉(zhuǎn)發(fā)器（實(shí)際上也是一個(gè)動(dòng)態(tài)鏈接庫(kù)，在Linux-i386中文件名是：libjnidispatch.so）可以自動(dòng)實(shí)現(xiàn)Java與C之間的數(shù)據(jù)類(lèi)型映射。從性能上會(huì)比JNI技術(shù)調(diào)用動(dòng)態(tài)鏈接庫(kù)要低。
1.簡(jiǎn)單寫(xiě)個(gè)windows下的dll,文件命名為forjava.dll,其中一個(gè)add函數(shù),采用stdcall調(diào)用約定

復(fù)制代碼代碼如下:

main.h文件
#ifndef __MAIN_H__
#define __MAIN_H__

#include <windows.h>

/* To use this exported function of dll, include this header
* in your project.
*/

#ifdef BUILD_DLL
#define DLL_EXPORT __declspec(dllexport) __stdcall
#else
#define DLL_EXPORT __declspec(dllimport) __stdcall
#endif

#ifdef __cplusplus
extern "C"
{
#endif

int DLL_EXPORT add(int a,int b);

#ifdef __cplusplus
}
#endif

#endif // __MAIN_H__

main.cpp

#include "main.h"

// a sample exported function
int DLL_EXPORT add(int a ,int b)
{
    return a+b;
}

extern "C" DLL_EXPORT BOOL APIENTRY DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
    switch (fdwReason)
    {
        case DLL_PROCESS_ATTACH:
            // attach to process
            // return FALSE to fail DLL load
            break;

        case DLL_PROCESS_DETACH:
            // detach from process
            break;

        case DLL_THREAD_ATTACH:
            // attach to thread
            break;

        case DLL_THREAD_DETACH:
            // detach from thread
            break;
    }
    return TRUE; // succesful
}

2.將jna.jar導(dǎo)入eclipse工程中,java代碼如下

復(fù)制代碼代碼如下:

//import com.sun.jna.Library; cdecl call調(diào)用約定 
import com.sun.jna.Native; 
import com.sun.jna.Platform; 
import com.sun.jna.win32.StdCallLibrary; 

public class main { 

    public interface CLibrary extends StdCallLibrary { //cdecl call調(diào)用約定時(shí)為L(zhǎng)ibrary 
        CLibrary INSTANCE = (CLibrary)Native.loadLibrary("forjava",CLibrary.class); 
        public int add(int a,int b); 
    } 

    public static void main(String[] args) { 
        System.out.print(CLibrary.INSTANCE.add(2,3)); 
    } 
}
 