JAVA调用动态链接库

上一篇《JAVA本地接口（JNI）》中介绍了JAVA的JNI技术，通过JAVA自有的方式调用动态链接库，这一篇将继续为大家介绍使用其他方式调用动态链接库。
首先，我们编写一个用于测试的链接库

头文件 print.h

#ifdef DLL_IMPLEMENT  
   #define DLL_API __declspec(dllexport)  
#else  
   #define DLL_API __declspec(dllimport)  
#endif 

#ifndef _Included_PRINT
   #define _Included_PRINT
   #ifdef __cplusplus
      extern "C" {
   #endif
   DLL_API void print();
   DLL_API void print2(int i);
   DLL_API int print3(int i);

   #ifdef __cplusplus
      }
   #endif
#endif

源文件 print.c

#define DLL_IMPLEMENT 
#include 
#include "print.h"
DLL_API void print()
{
   printf("invoke print...");
}
DLL_API void print2(int i)
{
   printf("invoke print %d...", i);
}
DLL_API int print3(int i)
{
   return i;
}

使用c编译器对其进行编译：cl -LD print.c -Feprint.dll
然后我们将生成的print.dll放在系统的system32文件夹下，至此准备工作完成。

JNative

JNative是Java to native interface的缩写，使用JNative，我们可以很方便的调用动态链接库，使用示例如下：

import org.xvolks.jnative.JNative;
import org.xvolks.jnative.Type;

public class JNativeTest
{
       
   public static void main(String[] args) throws Exception
   {
      // 加载动态链接库
      JNative print = new JNative("print.dll", "print");
      // 执行函数
      print.invoke();
      JNative print2 = new JNative("print.dll", "print2");
      // 设置函数形参
      print2.setParameter(0, 2);
      print2.invoke();
      JNative print3 = new JNative("print.dll", "print3");
      // 设置返回值类型
      print3.setRetVal(Type.INT);
      print3.setParameter(0, 3);
      print3.invoke();
      // 获得运行结果
      String result = print3.getRetVal();
      System.out.println("print3:" + result);
   }
}

下面再给出一个使用JNative获得系统时间的示例：

import org.xvolks.jnative.JNative;
import org.xvolks.jnative.exceptions.NativeException;
import org.xvolks.jnative.misc.basicStructures.AbstractBasicData;
import org.xvolks.jnative.pointers.Pointer;
import org.xvolks.jnative.pointers.memory.MemoryBlockFactory;
import org.xvolks.jnative.util.Kernel32.SystemTime;

public class JNativeDemo extends AbstractBasicData<JNativeDemo>
{
       
   public short wYear;
   public short wMonth;
   public short wDayOfWeek;
   public short wDay;
   public short wHour;
   public short wMinute;
   public short wSecond;
   public short wMilliseconds;

   /**
    * 分配内存，并返回指针
    */
   public Pointer createPointer() throws NativeException
   {
      pointer = new Pointer(MemoryBlockFactory.createMemoryBlock(getSizeOf()));
      return pointer;
   }

   /**
    * 内存大小
    */
   public int getSizeOf()
   {
      return 8 * 2;
   }

   /**
    * 获取通过内存指针解析出结果
    */
   public JNativeDemo getValueFromPointer() throws NativeException
   {
      wYear = getNextShort();
      wMonth = getNextShort();
      wDayOfWeek = getNextShort();
      wDay = getNextShort();
      wHour = getNextShort();
      wMinute = getNextShort();
      wSecond = getNextShort();
      wMilliseconds = getNextShort();
      return this;
   }

   public JNativeDemo() throws NativeException
   {
      super(null);
      createPointer();
   }

   public String toString()
   {
      return wYear + "/" + wMonth + "/" + wDay + " at + " + wHour + ":"
            + wMinute + ":" + wSecond + ":" + wMilliseconds;
   }

   public static SystemTime GetSystemTime() throws NativeException,
         IllegalAccessException
   {
      // 创建对象
      JNative nGetSystemTime = new JNative("Kernel32.dll", "GetSystemTime");
      SystemTime systemTime = new SystemTime();
      // 设置参数
      nGetSystemTime.setParameter(0, systemTime.getPointer());
      nGetSystemTime.invoke();
      // 解析结构指针内容
      return systemTime.getValueFromPointer();
   }

   public static void main(String[] args) throws NativeException,
         IllegalAccessException
   {
      System.err.println(GetSystemTime());
   }
}

JNA

JNA（Java Native Access ）提供一组Java工具类用于在运行期动态访问系统本地库（native library：如Window的dll）而不需要编写任何Native/JNI代码。开发人员只要在一个java接口中描述目标native library的函数与结构，JNA将自动实现Java接口到native function的映射。

使用示例：

import com.sun.jna.Library;
import com.sun.jna.Native;

public class JNADemo
{
       
   // 定义接口CLibrary，继承自com.sun.jna.Library
   public interface CLibrary extends Library
   {
       
      // 定义并初始化接口的静态变量
      CLibrary Instance = (CLibrary) Native
            .loadLibrary("print", CLibrary.class);

      // 函数声明
      void print();

      void print2(int i);

      int print3(int i);

   }

   public static void main(String[] args)
   {
      CLibrary.Instance.print();
      CLibrary.Instance.print2(2);
      System.out.println("print3:" + CLibrary.Instance.print3(3));
   }
}

JNative和JNA都可以实现对DLL的调用，但二者各有优缺点，需要根据实际情况选择。