Here is a very simple yet complete working sample of a
low level Windows keyboard hook within a Swing application.
Please try it.

//
// FrameTest.java
//
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class FrameTest extends JFrame {
   private JPanel mainPanel;
   private JTextArea mainTextArea;
   private HookTest hook;

   public static void main(String[] args) {
       SwingUtilities.invokeLater(new Runnable() {
           public void run() {
               new FrameTest().setVisible(true);
           }
       });
   }

   FrameTest() {
       super("FrameTest");
       setSize(200, 200);
       setDefaultCloseOperation(EXIT_ON_CLOSE);
       mainPanel = new JPanel();
       mainPanel.setLayout(new BorderLayout());
       mainTextArea = new JTextArea();
       mainPanel.add(mainTextArea, BorderLayout.CENTER);
       getContentPane().add(mainPanel);
       addWindowListener(new WindowAdapter() {
           public void windowClosing(WindowEvent event) {
               hook.unRegisterHook();
           }
       });
       new Thread() {
           public void run() {
               hook = new HookTest();
               hook.registerHook();
           }
       }.start();
   }
}

//
// HookTest.java
//
public class HookTest {
   static {
       System.loadLibrary("HookTest");
   }

   void processKey(int key, boolean pressed) {
       System.out.println("Java: HookTest.processKey - key = " + key +
(pressed ? " pressed" : " released"));
   }

   native void registerHook();
   native void unRegisterHook();
}

//
// HookTest.h
//
#ifndef _Included_HookTest
#define _Included_HookTest

#include <jni.h>

#ifdef __cplusplus
extern "C" {
#endif

JNIEXPORT void JNICALL Java_HookTest_registerHook(JNIEnv * env, jobject
obj);

JNIEXPORT void JNICALL Java_HookTest_unRegisterHook(JNIEnv * env,
jobject obj);

#ifdef __cplusplus
}
#endif

#endif /* _Included_HookTest */

//
// HookTest.cpp
//
#include <windows.h>
#include "HookTest.h"

HINSTANCE hInst = NULL;
JavaVM * jvm = NULL;
jobject hookObj = NULL;
jmethodID processKeyID = NULL;
DWORD hookThreadId = 0;

extern "C" BOOL APIENTRY DllMain(HINSTANCE _hInst, DWORD reason, LPVOID
reserved) {
   switch (reason) {
   case DLL_PROCESS_ATTACH:
       printf("C++: DllMain - DLL_PROCESS_ATTACH.\n");
       hInst = _hInst;
       break;
   default:
       break;
   }

   return TRUE;
}

LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM
lParam) {
   JNIEnv * env;
   KBDLLHOOKSTRUCT * p = (KBDLLHOOKSTRUCT *)lParam;

   if (jvm->AttachCurrentThread((void **)&env, NULL) >= 0) {
       switch (wParam) {
       case WM_KEYDOWN:
       case WM_SYSKEYDOWN:
           printf("C++: LowLevelKeyboardProc - Key pressed\n");
           env->CallVoidMethod(hookObj, processKeyID, p->vkCode,
true);
           break;
       case WM_KEYUP:
       case WM_SYSKEYUP:
           printf("C++: LowLevelKeyboardProc - Key released\n");
           env->CallVoidMethod(hookObj, processKeyID, p->vkCode,
false);
           break;
       default:
           break;
       }
   }
   else {
       printf("C++: LowLevelKeyboardProc - Error on the attach current
thread.\n");
   }

   return CallNextHookEx(NULL, nCode, wParam, lParam);
}

void MsgLoop() {
   MSG message;

   while (GetMessage(&message, NULL, 0, 0)) {
       TranslateMessage(&message);
       DispatchMessage(&message);
   }
}

JNIEXPORT void JNICALL Java_HookTest_registerHook(JNIEnv * env, jobject
obj) {
   HHOOK hookHandle = SetWindowsHookEx(WH_KEYBOARD_LL,
LowLevelKeyboardProc, hInst, 0);

   if (hookHandle == NULL) {
       printf("C++: Java_HookTest_registerHook - Hook failed!\n");
       return;
   }
   else {
       printf("C++: Java_HookTest_registerHook - Hook successful\n");
   }

   hookObj = env->NewGlobalRef(obj);
   jclass cls = env->GetObjectClass(hookObj);
   processKeyID = env->GetMethodID(cls, "processKey", "(IZ)V");
   env->GetJavaVM(&jvm);
   hookThreadId = GetCurrentThreadId();

   MsgLoop();

   if (!UnhookWindowsHookEx(hookHandle))
       printf("C++: Java_HookTest_registerHook - Unhook failed\n");

   else
       printf("C++: Java_HookTest_registerHook - Unhook
successful\n");
}

JNIEXPORT void JNICALL Java_HookTest_unRegisterHook(JNIEnv *env,
jobject object) {
   if (hookThreadId == 0)
       return;

   printf("C++: Java_HookTest_unRegisterHook - call
PostThreadMessage.\n");
   PostThreadMessage(hookThreadId, WM_QUIT, 0, 0L);
}

Regards