nanaji

See the next few lines containing Java Code:

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. }

This code above shows us how to implement a single instance application. But let me explain it.

The getMonitoredVMs(int processPid) method receives as paramter the current application PID, and catch the application name that is called from command line, for example, the application was started from c:\java\app\test.jar path, then the value variable is "c:\\java\\app\\teste.jar". This way, we will catch just application name on the line 17 of the code below.
After that, we search JVM for antoher process with the same name, if we found it and the application PID is different, it means that is the second application instance.

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. }

The problem of all this code are the imports, that are defined only in the file tools.jar file and has a size of 11MB. But to solve this problem, I have unpacked this file and a packed a new file called VM.ZIP only with the necessary classes, and it has a size of just 81kb.

PS: When you're debbuging the code, the processName variable will be assigned to Class Main project, for example, the name of its class is Principal and is in the package com.main, then the variable processName will be assigned as "com.main.Principal." To test you have to open another instance of Debug and it will work.
In the release case, it will be showed the application name as we can see in the line code JOptionPane.showMessageDialog(null,processName).


Below the file attached VM.zip.
VM.zip