1. // imports
   2. import sun.management.ConnectorAddressLink;  
   3. import sun.jvmstat.monitor.HostIdentifier;  
   4. import sun.jvmstat.monitor.Monitor;  
   5. import sun.jvmstat.monitor.MonitoredHost;  
   6. import sun.jvmstat.monitor.MonitoredVm;  
   7. import sun.jvmstat.monitor.MonitoredVmUtil;  
   8. import sun.jvmstat.monitor.MonitorException;  
   9. import sun.jvmstat.monitor.VmIdentifier;  
  10.  
  11. public static void main(String args[]) {  
  12.         /* The method ManagementFactory.getRuntimeMXBean() returns an identifier with applcation PID
  13.             in the Sun JVM, but each jvm may have you own implementation.
  14.             So in anothers jvm, other than Sun, this code may not work., :(
  15.         */  
  16.         RuntimeMXBean rt = ManagementFactory.getRuntimeMXBean();  
  17.         final int runtimePid = Integer.parseInt(rt.getName().substring(0,rt.getName().indexOf("@")));  
  18.                                
  19.         java.awt.EventQueue.invokeLater(new Runnable() {  
  20.             public void run() {  
  21.                  
  22.                 // If exists another instance, show message and terminates the current instance.  
  23.                 // Otherwise starts application.  
  24.                 if (getMonitoredVMs(runtimePid))  
  25.                 {  
  26.                     new MainFrame().setVisible(true);  
  27.                 } else  
  28.                     JOptionPane.showMessageDialog(null,"There is another instance of this application running.");  
  29.                  
  30.             }  
  31.         });  
  32. }

1. private static boolean getMonitoredVMs(int processPid) {  
   2.         MonitoredHost host;  
   3.         Set vms;  
   4.         try {  
   5.             host = MonitoredHost.getMonitoredHost(new HostIdentifier((String)null));  
   6.             vms = host.activeVms();  
   7.         } catch (java.net.URISyntaxException sx) {  
   8.             throw new InternalError(sx.getMessage());  
   9.         } catch (MonitorException mx) {  
  10.             throw new InternalError(mx.getMessage());  
  11.         }  
  12.         MonitoredVm mvm = null;  
  13.         String processName = null;  
  14.         try{  
  15.             mvm = host.getMonitoredVm(new VmIdentifier(String.valueOf(processPid)));  
  16.             processName = MonitoredVmUtil.commandLine(mvm);  
  17.             processName = processName.substring(processName.lastIndexOf("\\") + 1,processName.length());  
  18.             mvm.detach();  
  19.         } catch (Exception ex) {  
  20.              
  21.         }  
  22.        // This line is just to verify the process name. It can be removed.
  23.         JOptionPane.showMessageDialog(null,processName);  
  24.         for (Object vmid: vms) {  
  25.             if (vmid instanceof Integer) {  
  26.                 int pid = ((Integer) vmid).intValue();  
  27.                 String name = vmid.toString(); // default to pid if name not available  
  28.                 try {  
  29.                      mvm = host.getMonitoredVm(new VmIdentifier(name));  
  30.                      // use the command line as the display name  
  31.                      name =  MonitoredVmUtil.commandLine(mvm);  
  32.                      name = name.substring(name.lastIndexOf("\\")+1,name.length());  
  33.                      mvm.detach();  
  34.                      if ((name.equalsIgnoreCase(processName)) && (processPid != pid))  
  35.                          return false;  
  36.                 } catch (Exception x) {  
  37.                      // ignore  
  38.                 }  
  39.             }  
  40.         }  
  41.          
  42.         return true;  
  43. }