Show previous instance of RCP application - eclipse

Question

I had an rcp application which runs for only first run, when a user attempts to re-execute the application, second instance behaves as a client which encodes and sends its arguments over the socket to the first instance which acts as a server and then exits silently. The first instance receives and decodes that message, then behaves as if it had been invoked with those arguments.
so far so good i made internal protocol specification for passing arguments between two instances.
I could not bring the first instance(RCP application) to front. It is in minimized state only,
this is in continuation to my previous question
the change i made to previous post is start method of application class
public Object start(IApplicationContext context) throws Exception {
if (!ApplicationInstanceManager.registerInstance()) {
return IApplication.EXIT_OK;
}
ApplicationInstanceManager
.setApplicationInstanceListener(new ApplicationInstanceListener() {
public void newInstanceCreated() {
Display.getDefault().asyncExec(new Runnable() {
public void run() {
System.out.println("New instance detected...");
//Display.getCurrent().getActiveShell()
.forceActive();// this gives null
// pointer exception
// hence commented
}
});
}
});
Display display = PlatformUI.createDisplay();
try {
int returnCode = PlatformUI.createAndRunWorkbench(display,
new ApplicationWorkbenchAdvisor());
if (returnCode == PlatformUI.RETURN_RESTART)
return IApplication.EXIT_RESTART;
else
return IApplication.EXIT_OK;
} finally {
display.dispose();
}
}
below line is stopping me to bring Application to front
Display.getCurrent().getActiveShell().forceActive();
generates null pointer exception at getActiveShell()
how can i maximize the previous instance or bring it to front

Answer 1

I wrote an instance manager to restrict my RCP to a single instance.
Here's the code that goes in Application.java, in the start method:
if (!ApplicationInstanceManager.registerInstance()) {
return IApplication.EXIT_OK;
}
ApplicationInstanceManager
.setApplicationInstanceListener(new ApplicationInstanceListener() {
public void newInstanceCreated() {
Display.getDefault().asyncExec(new Runnable() {
public void run() {
if (DEBUG)
System.out.println("New instance detected...");
Display.getCurrent().getActiveShell().forceActive();
}
});
}
});
Here's the listener interface:
public interface ApplicationInstanceListener {
public void newInstanceCreated();
}
And here's the Manager class:
public class ApplicationInstanceManager {
private static final boolean DEBUG = true;
private static ApplicationInstanceListener subListener;
/** Randomly chosen, but static, high socket number */
public static final int SINGLE_INSTANCE_NETWORK_SOCKET = 44331;
/** Must end with newline */
public static final String SINGLE_INSTANCE_SHARED_KEY = "$$RabidNewInstance$$\n";
/**
* Registers this instance of the application.
*
* #return true if first instance, false if not.
*/
public static boolean registerInstance() {
// returnValueOnError should be true if lenient (allows app to run on
// network error) or false if strict.
boolean returnValueOnError = true;
// try to open network socket
// if success, listen to socket for new instance message, return true
// if unable to open, connect to existing and send new instance message,
// return false
try {
final ServerSocket socket = new ServerSocket(
SINGLE_INSTANCE_NETWORK_SOCKET, 10, InetAddress
.getLocalHost());
if (DEBUG)
System.out
.println("Listening for application instances on socket "
+ SINGLE_INSTANCE_NETWORK_SOCKET);
Thread instanceListenerThread = new InstanceListenerThread(socket);
instanceListenerThread.start();
// listen
} catch (UnknownHostException e) {
EclipseLogging.logError(RabidPlugin.getDefault(),
RabidPlugin.PLUGIN_ID, e);
return returnValueOnError;
} catch (IOException e) {
return portTaken(returnValueOnError, e);
}
return true;
}
private static boolean portTaken(boolean returnValueOnError, IOException e) {
if (DEBUG)
System.out.println("Port is already taken. "
+ "Notifying first instance.");
try {
Socket clientSocket = new Socket(InetAddress.getLocalHost(),
SINGLE_INSTANCE_NETWORK_SOCKET);
OutputStream out = clientSocket.getOutputStream();
out.write(SINGLE_INSTANCE_SHARED_KEY.getBytes());
out.close();
clientSocket.close();
System.out.println("Successfully notified first instance.");
return false;
} catch (UnknownHostException e1) {
EclipseLogging.logError(RabidPlugin.getDefault(),
RabidPlugin.PLUGIN_ID, e);
return returnValueOnError;
} catch (IOException e1) {
EclipseLogging
.logError(
RabidPlugin.getDefault(),
RabidPlugin.PLUGIN_ID,
"Error connecting to local port for single instance notification",
e);
return returnValueOnError;
}
}
public static void setApplicationInstanceListener(
ApplicationInstanceListener listener) {
subListener = listener;
}
private static void fireNewInstance() {
if (subListener != null) {
subListener.newInstanceCreated();
}
}
public static void main(String[] args) {
if (!ApplicationInstanceManager.registerInstance()) {
// instance already running.
System.out.println("Another instance of this application "
+ "is already running. Exiting.");
System.exit(0);
}
ApplicationInstanceManager
.setApplicationInstanceListener(new ApplicationInstanceListener() {
public void newInstanceCreated() {
System.out.println("New instance detected...");
// this is where your handler code goes...
}
});
}
public static class InstanceListenerThread extends Thread {
private ServerSocket socket;
public InstanceListenerThread(ServerSocket socket) {
this.socket = socket;
}
#Override
public void run() {
boolean socketClosed = false;
while (!socketClosed) {
if (socket.isClosed()) {
socketClosed = true;
} else {
try {
Socket client = socket.accept();
BufferedReader in = new BufferedReader(
new InputStreamReader(client.getInputStream()));
String message = in.readLine();
if (SINGLE_INSTANCE_SHARED_KEY.trim().equals(
message.trim())) {
if (DEBUG)
System.out.println("Shared key matched - "
+ "new application instance found");
fireNewInstance();
}
in.close();
client.close();
} catch (IOException e) {
socketClosed = true;
}
}
}
}
}
}

Answer 2

After your IApplication start up, you can also check and lock the OSGi instance location using org.eclipse.osgi.service.datalocation.Location.isSet() and org.eclipse.osgi.service.datalocation.Location.lock()
The location is usually retrieved from your Activator using code like:
public Location getInstanceLocation() {
if (locationTracker == null) {
Filter filter = null;
try {
filter = context.createFilter(Location.INSTANCE_FILTER);
} catch (InvalidSyntaxException e) {
// ignore this. It should never happen as we have tested the
// above format.
}
locationTracker = new ServiceTracker(context, filter, null);
locationTracker.open();
}
return (Location) locationTracker.getService();
}