v1.1.4a

Changed:
- PInstance knows and calls a function when another instance with the same port tries to open

Author: Paulsen

src/ooo/paulsen/demo/Demo.java

@@ -13,7 +13,6 @@
 import java.awt.event.KeyEvent;
 import java.awt.event.KeyListener;
 import java.io.IOException;
-import java.net.BindException;
 
 public class Demo {
 
@@ -39,13 +38,20 @@ public static void main(String[] args) {
     public Demo() {
 
         try {
-            PInstance p = new PInstance(8123);
-        } catch (BindException e) {
+            PInstance p = new PInstance(8123, new Runnable() {
+                @Override
+                public void run() {
+                    System.out.println("Focus that thing! Someone tried to open this exact program once again");
+                    f.setVisible(true);
+                    f.setState(JFrame.NORMAL);
+                    f.toFront();
+                    f.requestFocus();
+                }
+            });
+        } catch (IOException e) {
             System.out.println("Already runs");
-            JOptionPane.showMessageDialog(null,"Port 8123 already taken by another Process","Instance already running",JOptionPane.INFORMATION_MESSAGE);
+            JOptionPane.showMessageDialog(null, "Port 8123 already taken by another Process", "Instance already running", JOptionPane.INFORMATION_MESSAGE);
             System.exit(0);
-        } catch (IOException e) {
-            throw new RuntimeException(e);
         }
 
         frameTitle = "JPL-Demo - " + PSystem.getUserName() + "'s " + PSystem.getOSType() + "-System from " + PSystem.getUserDisplayLocation();

src/ooo/paulsen/utils/PInstance.java

@@ -4,38 +4,87 @@
 import java.net.BindException;
 import java.net.InetAddress;
 import java.net.ServerSocket;
+import java.net.Socket;
 
 /**
  * Used for singe-instance-Programms <br>
  * <a href="https://stackoverflow.com/questions/920386/how-to-allow-running-only-one-instance-of-a-java-program-at-a-time">Source</a>
  */
 public class PInstance {
 
-    private static int PORT;
-    private static ServerSocket socket;
+    private int PORT;
+    private Runnable connectAction;
+    private ServerSocket serverSocket;
 
     /**
      * Creates/reserves a local Port to indicate that this Program is running.
-     * @param port has to be in Range and not be allocated by <a href="https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml">another program</a>
-     * @throws BindException if Another Instance already exists
-     * <br>IOException if the socket failed
+     *
+     * @param port          has to be in Range and not be allocated by <a href="https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml">another program</a>
+     * @param connectAction is the Function that is called when some program connects to it
+     * @throws IOException if the socket failed or Another Instance already exists
      */
-    public PInstance(int port) throws IOException, BindException {
+    public PInstance(int port, Runnable connectAction) throws IOException {
         PORT = port;
+        this.connectAction = connectAction;
 
-        //Bind to localhost adapter with a zero connection queue
-        socket = new ServerSocket(PORT, 0, InetAddress.getByAddress(new byte[]{127, 0, 0, 1}));
+        callServer();
+        initServer();
+    }
+
+    /**
+     * Looks for a Server/Process that waits for a connection
+     */
+    private void callServer() {
+        try {
+            Socket s = new Socket("127.0.0.1", PORT);
+        } catch (IOException e) {
+            // No Other Instance found (or other error)
+        }
     }
 
     /**
+     * Inits Server
      *
+     * @throws IOException if the socket failed or Another Instance already exists
+     */
+    private void initServer() throws IOException {
+
+        //Bind to localhost adapter with a zero connection queue
+        serverSocket = new ServerSocket(PORT, 0, InetAddress.getByAddress(new byte[]{127, 0, 0, 1}));
+        Thread t = new Thread(new Runnable() {
+            @Override
+            public void run() {
+                while (true) {
+                    try {
+
+                        // look for connection
+                        serverSocket.accept();
+
+                        // execute Function if some other program connected (to e.g. focus the older UI-Instance)
+                        if (connectAction != null)
+                            connectAction.run();
+
+                        // close and reopen server
+                        serverSocket.close();
+                        serverSocket = new ServerSocket(PORT, 0, InetAddress.getByAddress(new byte[]{127, 0, 0, 1}));
+                    } catch (IOException e) {
+                        // Address already in Use
+                        throw new RuntimeException(e);
+                    }
+                }
+            }
+        });
+        t.start();
+    }
+
+    /**
      * @param port
      * @return if a local Program, which reserves/uses a Port, is running.
      */
     public static boolean isInstanceRunning(int port) {
         try {
             //Bind to localhost adapter with a zero connection queue
-            socket = new ServerSocket(port, 0, InetAddress.getByAddress(new byte[]{127, 0, 0, 1}));
+            ServerSocket serverSocket = new ServerSocket(port, 0, InetAddress.getByAddress(new byte[]{127, 0, 0, 1}));
         } catch (BindException e) {
             return true;
         } catch (IOException e) {