如何設置焦點已運行的應用程序？

Question

我正在使用一個ServerSocket端口來運行我的Java Swing應用程序的一個實例，所以如果用戶試圖打開該程序的另一個實例，我會向他顯示一條警告「另一個實例已經打開」。這工作正常，但沒有顯示此消息，我想設置專注於運行的應用程序本身，就像一些程序（MSN Messenger），即使它被最小化。

對於各種操作系統，是否有解決方案？

Answer 1

由於您使用服務器套接字我假設您使用java.net.BindException來檢測您的應用程序已在運行。如果您啓動第二個實例，則可以發送一條控制消息，指示您在退出之前先將應用程序標準化（如果已最小化）。

if (msg == BRING_TO_FRONT) { 
    frame.setState(Frame.NORMAL); 
    frame.toFront(); 
} 

Answer 2

我不知道這是絕對正確的，但這裏的最終代碼我用它爲我工作得很好：

public class Loader { 
private static final int PORT = 9999; 
private static ServerSocket serverSocket = null; // Server 
private static Socket socket = null; // CLient 
private static final String focusProgram = "FOCUS"; 

public static void main(String[] args) { 
    if(!isProgramRunning()) { 
     Main main = new Main(); 
     main.setVisible(true); 
    } 
    else { 
     System.exit(2); 
    } 
} 

private static boolean isProgramRunning() { 
    try { 
     serverSocket = new ServerSocket(PORT,0,InetAddress.getByAddress(new byte[] {127,0,0,1})); // Bind to localhost adapter with a zero connection queue. 
     SwingWorker<String, Void> anotherThread = new SwingWorker<String, Void>() { // Do some code in another normal thread. 
      @Override 
      public String doInBackground() { // This method is to execute a long code in the other thread in background. 
       serverSocketListener(); 
       return ""; 
      } 
     }; 
     anotherThread.execute(); // Execute the other tread. 
    } 
    catch (BindException e) { 
     System.err.println("Already running."); 
     clientSocketListener(); 

     return true; 
    } 
    catch (IOException e) { 
     System.err.println("Unexpected error."); 
     e.printStackTrace(); 

     return true; 
    } 

    return false; 
} 

public static void serverSocketListener() { // Server socket 
    try { 
     System.out.println("Listener socket opened to prevent any other program instance."); 
     socket = serverSocket.accept(); 
     BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream())); 

     if(in.readLine().equals(focusProgram)) { // Restore the opened instance however you want. 
      Global.getCurrentFrame().setState(Frame.NORMAL); 
      Global.getCurrentFrame().toFront(); 
     }  
    } catch (IOException e) { 
     e.printStackTrace(); 
     System.exit(-1); 
    } 
} 

public static void clientSocketListener() { // Client socket 
    try{ 
     socket = new Socket(InetAddress.getByAddress(new byte[] {127,0,0,1}), PORT); 
     PrintWriter out = new PrintWriter(socket.getOutputStream(), true); 
     out.println(focusProgram); 
    } catch (IOException e) { 
     System.out.println("No I/O"); 
     System.exit(1); 
    } 
} 

}