问题
We have an application based on the netbeans rich client platform.
Default behaviour is that only one instance of the software can run, and this can be overridden by specifying a different user-dir as argument when starting the application.
Are there any alternatives to this? Our clients rely on being able to run several instances of the application.
(We would prefer if we didnt have to implement our own launcher that examines netbeans userdir for locks to pass alternative userdirs)
Is there a build-in way in the netbeans RCP to easily support multiple instances?
cheers /B
回答1:
So, unable to find a proper way to do this (seems like it will be available with nb 7 though through a new launcher input parameter), my workmate implemented it in a somewhat hackish way.
He created an alternative main-class, which checks and manipulates the user-dir property so each instance gets its own userdir.
Im still surprised that netbeans does not have this functionality!
import java.io.File;
import org.netbeans.Main;
/**
* Launches Netbeans Rich Client Platform application where mulitple instances of
* the application can run simultaneously for the same user.
* <p>
* Netbeans does not allow to run several instances of an application for the same
* user simultaneously, but this class does the job by fooling Netbeans.
* If an instance is already running then a new folder is created and used for this instance.
* </p>
* <p>
* This is quite tricky and this class is indeed a hack to override Netbeans behaviour.
* An example makes it a little easier to understand, when application is first started
* Netbeans userdir is set from a configuration file like {@code etc/xxxxx.conf} to something like:<br>
* {@code /home/username/.xxxxx/dev/} which includes a lock file.
* <br>
* If application is started again then this lock file is checked and Netbeans tries to connect to the other instance through a socket.
* This class does the trick by never using this folder but instead creating unique directories for each instance like:<br>
* {@code /home/username/.xxxxx/instance_01/netbeans/}<br>
* {@code /home/username/.xxxxx/instance_02/netbeans/}<br>
* {@code /home/username/.xxxxx/instance_03/netbeans/}<br>
* ...
* </p>
*
*/
public class MultipleInstancesMain
{
/** Key for Netbeans default user dir */
private static final String NETBEANS_USER = "netbeans.user";
/** Argument to Netbeans for alternate user dir */
private static final String USERDIR_ARG = "--userdir";
/** Like "C:\Documents and Settings\username\Application Data\.xxxxx" or "/home/username/.xxxxx" */
private static final File MAIN_DIR = getMainDir();
/** Sub dir of MAIN_DIR for each instance of application */
private static final String INSTANCE_DIR = "instance";
/** Sub dir of INSTANCE_DIR where netbeans stores it's settings, logs and cache */
private static final String NETBEANS_SUBDIR = "netbeans";
/** Name of Netbeans lock file inside of NETBEANS_SUBDIR */
private static final String LOCKFILE = "lock";
/** Max number of instance directories we allow */
private static final int MAX_DIR_COUNT = 999;
/** Padding of instance dir */
private static final String PAD = "000";
private static final int PAD_LENGTH = PAD.length();
/**
* Lock file could be present even though application is not running (after crash).
* So we treat it as "dead" after some time, to prevent "dead directories".
*/
private static final long LOCKFILE_MAX_AGE_IN_MILLIS = 1000L * 60L * 60L * 24L * 30L; // 30 days
/**
* Launches application with multiple instances support.
* @param args command line arguments
*/
public static void main(String[] args) throws Exception
{
// Get directory for this instance
String[] userDir = new String[2];
userDir[0] = USERDIR_ARG;
userDir[1] = getNetbeansDir();
// Remove default dir and set this class not to run again
deleteDefaultNetbeansDir();
System.clearProperty("netbeans.mainclass");
// Start Netbeans again with new userdir and default main class
startNetbeans(args, userDir);
}
/**
* Starts Netbeans.
* @param oldArgs command line arguments
* @param newArgs new arguments added
*/
private static void startNetbeans(String[] oldArgs, String[] newArgs) throws Exception
{
String[] args = new String[oldArgs.length + newArgs.length];
for (int i = 0; i <oldArgs.length; i++)
{
args[i] = oldArgs[i];
}
for (int i = 0; i < newArgs.length; i++)
{
args[oldArgs.length + i] = newArgs[i];
}
Main.main(args);
}
/**
* @return the directory that Netbeans will use for this instance of the application
*/
private static String getNetbeansDir()
{
for(int i = 1; i <= MAX_DIR_COUNT; i++)
{
File instanceDir = getSuffixedInstanceDir(i);
if (isLockFileFree(instanceDir))
{
File dirToUse = new File(instanceDir, NETBEANS_SUBDIR);
return dirToUse.getAbsolutePath();
}
}
// This would probably never happen, but we don't want an eternal loop above
String errorMessage = String.format("Unable to find Netbeans userdir, %s dirs checked in '%s'",
MAX_DIR_COUNT, MAIN_DIR.getAbsolutePath());
throw new RuntimeException(errorMessage);
}
private static File getSuffixedInstanceDir(int count)
{
String suffix = PAD + count;
suffix = suffix.substring(suffix.length() - PAD_LENGTH);
File suffixedDir = new File(MAIN_DIR, INSTANCE_DIR + "_" + suffix);
return suffixedDir;
}
/**
* Checks is if Netbeans lock file is free.
* @param instanceDir directory to look for Netbeans directory and lock file in
* @return true if {@code instanceDir} does not have a Netbeans folder with a occupied lock file
*/
private static boolean isLockFileFree(File instanceDir)
{
File netbeansDir = new File(instanceDir, NETBEANS_SUBDIR);
File lockFile = new File(netbeansDir, LOCKFILE);
if (lockFile.exists())
{
return deleteLockFileIfOldEnough(lockFile);
}
else
{
return true;
}
}
/**
* Deletes the lock file if it's old enough.
* @param lockFile lock file to delete
* @return true if it was deleted
* @see #LOCKFILE_MAX_AGE_IN_MILLIS
*/
private static boolean deleteLockFileIfOldEnough(File lockFile)
{
long currentTime = System.currentTimeMillis();
long fileCreated = lockFile.lastModified();
long ageInMillis = currentTime - fileCreated;
if (ageInMillis > LOCKFILE_MAX_AGE_IN_MILLIS)
{
return lockFile.delete();
}
else
{
return false;
}
}
/**
* Netbeans is started with a default userdir, but we need to have a unique dir for each instance.
* Main dir is the directory where directories of all instances are.
* @return main directory in users home area where application settings, logs and cache is stored
*/
private static File getMainDir()
{
String defaultNetbeansDir = System.getProperty(NETBEANS_USER);
File mainDir = new File(defaultNetbeansDir).getParentFile();
return mainDir;
}
/**
* Since we don't use default Netbeans dir at all, we remove it completely.
*/
private static void deleteDefaultNetbeansDir()
{
File defaultNetbeansDir = new File(System.getProperty(NETBEANS_USER));
Thread t = new Thread(new DirectoryDeleter(defaultNetbeansDir), "NetbeansDirDeleter");
t.start();
}
/**
* There are unpredictable behaviour when deleting Netbeans default directory, sometime it succeeds and sometimes not.
* But after some attempts it always succeeds, by deleting it in the background it will eventually be deleted.
* @author username
*/
private static class DirectoryDeleter implements Runnable
{
private static final long SLEEP_TIME = 3000;
private final File dirToDelete;
DirectoryDeleter(File dirToDelete)
{
this.dirToDelete = dirToDelete;
}
/**
* @see java.lang.Runnable#run()
*/
public void run()
{
while(!deleteDirOrFile(dirToDelete))
{
try
{
Thread.sleep(SLEEP_TIME);
}
catch (InterruptedException e)
{
// No idea to do anything here, should never happen anyway...
continue;
}
}
}
/**
* Deletes a file or directory
* @param dirFile directory or file to delete
* @return true if deletion succeeded
*/
private boolean deleteDirOrFile(File dirFile)
{
if (dirFile.isDirectory())
{
for (File f : dirFile.listFiles())
{
boolean deleted = deleteDirOrFile(f);
if (!deleted)
{
return false;
}
}
}
// The directory is now empty so delete it
return dirFile.delete();
}
}
}
回答2:
I'm the mysterious developer who wrote the MultipleInstancesMain class above =)
As answer to the questions by Swati Sharma and uvaraj above, these notes might help:
(1) The alternative main class above should work for applications built on Netbeans Platform 6.5.1 (our does), other versions I don't know about.
(2) We keep this class in a tiny project that is built by the main build.xml ant script of our application (the one in the "suite" module). The jar is then copied to the /[appname]/modules/ folder (so it's on Netbeans classpath)
(3) The separate project can NOT be a Netbeans module, I guess there will be cyclic dependency or Netbeans classloader can't handle it or something like that.
(4) Our application is then started by adding parameter to configuration file /[appname]/etc/.conf:
default_options="-J-Dnetbeans.mainclass=com.appname.startup.MultipleInstancesMain"
Hope it helps // Uhlén
来源：https://stackoverflow.com/questions/615708/running-several-instances-of-netbeans-rcp-application-simultaneously