JNA介绍

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。

优点

JNA可以让你像调用一般java方法一样直接调用本地方法。就和直接执行本地方法差不多，而且调用本地方法还不用额外的其他处理或者配置什么的，也不需要多余的引用或者编码，使用很方便。

JNA描述

JNA类库使用一个很小的本地类库sub 动态的调用本地代码。程序员只需要使用一个特定的java接口描述一下将要调用的本地代码的方法的结构和一些基本属性。这样就省了为了适配多个平台而大量的配置和编译代码。因为调用的都是JNA提供的公用jar 包中的接口。

JNA简单使用

JNA实现WINDOWS下全局鼠标键盘钩子

package jna_test;
  
import com.sun.jna.platform.win32.*;
import com.sun.jna.platform.win32.WinUser.*;
import com.sun.jna.platform.win32.WinDef.HMODULE;
import com.sun.jna.platform.win32.WinDef.LRESULT;
import com.sun.jna.platform.win32.WinDef.WPARAM;
import com.sun.jna.platform.win32.WinUser.HHOOK;
import com.sun.jna.platform.win32.WinUser.KBDLLHOOKSTRUCT;
import com.sun.jna.platform.win32.WinUser.LowLevelKeyboardProc;
import com.sun.jna.win32.WinUser.Mouse.LowLevelMouseProc;
import com.sun.jna.win32.WinUser.Mouse.MOUSEHOOKSTRUCT;
  
public class MouseLLHook {
     
    // 鼠标钩子函数里判断按键类型的常数
    public static final int WM_LBUTTONUP = 514;
    public static final int WM_LBUTTONDOWN = 513;
    public static final int WM_RBUTTONUP = 517;
    public static final int WM_RBUTTONDOWN = 516;
    public static final int WM_MOUSEHWHEEL = 526;
    public static final int WM_MOUSEWHEEL = 522;
    public static final int WM_MOUSEMOVE = 512;
      
    static HHOOK mouseHHK,keyboardHHK;//鼠标、键盘钩子的句柄
    static LowLevelMouseProc mouseHook;//鼠标钩子函数
    static LowLevelKeyboardProc keyboardHook;//键盘钩子函数
      
    // 安装钩子
    static void setHook() {
        HMODULE hMod = Kernel32.INSTANCE.GetModuleHandle(null);
        mouseHHK = User32.INSTANCE.SetWindowsHookEx(WinUser.WH_MOUSE_LL, mouseHook, hMod, 0);
        keyboardHHK = User32.INSTANCE.SetWindowsHookEx(WinUser.WH_KEYBOARD_LL, keyboardHook, hMod, 0);      
    }
      
    //卸载钩子
    static void unhook() {
        User32.INSTANCE.UnhookWindowsHookEx(keyboardHHK);
        User32.INSTANCE.UnhookWindowsHookEx(mouseHHK);     
    }
      
    public static void main(String[] args) {
          
        keyboardHook = new LowLevelKeyboardProc() {
              
            @Override
            //该函数参数的意思参考：http://msdn.microsoft.com/en-us/library/windows/desktop/ms644985(v=vs.85).aspx
            public LRESULT callback(int nCode, WPARAM wParam, KBDLLHOOKSTRUCT lParam) {
                int w = wParam.intValue();
                //按下alt键时w=.WM_SYSKEYDOWN; 按下其他大部分键时w=WinUser.WM_KEYDOWN
                if(w==WinUser.WM_KEYDOWN || w==WinUser.WM_SYSKEYDOWN)
                    System.out.println("key down: vkCode = "+lParam.vkCode);
                else if(w==WinUser.WM_KEYUP || w==WinUser.WM_SYSKEYUP)
                    System.out.println("key up: vkCode = "+lParam.vkCode);
                  
                // 如果按下'q'退出程序，'q'的vkCode是81
                if(lParam.vkCode==81) {
                    unhook();
                    System.err.println("program terminated.");
                    System.exit(0);
                }
                return User32.INSTANCE.CallNextHookEx(keyboardHHK, nCode, wParam, lParam.getPointer());
            }
        };
          
        mouseHook = new LowLevelMouseProc() {
              
            @Override
            //该函数参数的意思参考：http://msdn.microsoft.com/en-us/library/windows/desktop/ms644986(v=vs.85).aspx
            public LRESULT callback(int nCode, WPARAM wParam, MOUSEHOOKSTRUCT lParam) {
                switch (wParam.intValue()) {
                case WM_MOUSEMOVE:
                    System.out.print("mouse moved:");
                    break;
                case WM_LBUTTONDOWN:
                    System.out.print("mouse left button down:");
                    break;
                case WM_LBUTTONUP:
                    System.out.print("mouse left button up");
                    break;
                case WM_RBUTTONUP:
                    System.out.print("mouse right button up:");
                    break;
                case WM_RBUTTONDOWN:
                    System.out.print("mouse right button down:");
                    break;
                case WM_MOUSEWHEEL:
                    System.out.print("mouse wheel rotated:");
                    break;             
                }
                System.out.println("("+lParam.pt.x+","+lParam.pt.y+")");
                return User32.INSTANCE.CallNextHookEx(mouseHHK, nCode, wParam, lParam.getPointer());
            }
        };
          
        System.out.println("press 'q' to quit.");
        setHook();     
                  
        int result;
        MSG msg = new MSG();
        // 消息循环
        // 实际上while循环一次都不执行，这些代码的作用我理解是让程序在GetMessage函数这里阻塞，不然程序就结束了。
        while ((result = User32.INSTANCE.GetMessage(msg, null, 0, 0)) != 0) {          
            if (result == -1) {
                System.err.println("error in GetMessage");
                unhook();
                break;
            } else {
                User32.INSTANCE.TranslateMessage(msg);               
                User32.INSTANCE.DispatchMessage(msg);
            }
        }
        unhook();
    }
}