Learning lifecycle - OSGi in Action - page 90

explicitly resolve the bundle, because the specification requires the framework to
implicitly resolve the bundle if it's not already resolved. If the bundle's dependencies
can't be resolved, start() throws a BundleException and the bundle can't be used
until its dependencies are satisfied. If this happens, you'll typically install additional
bundles to satisfy the missing dependencies and try to start the bundle again.
I f t h e b u n d l e h a s a n a c t i v a t o r, t h e f r a m e w o r k i n v o k e s t h e BundleActivator.start()
method when starting the bundle. Any exceptions thrown from the activator result in
a failed attempt to start the bundle and an exception
being thrown from Bundle.start() . One last case where
an exception may result is if a bundle tries to start itself;
the specification says attempts to do so should result in
an IllegalStateException .
STOP COMMAND
That's it for starting bundles. Now we can look at stop-
ping bundles, which is similar to starting them; see the
next listing and figure 3.10.

Active

Resolved

Stop

Stopping

Figure 3.10 The stop-related
portion of the bundle lifecycle
state diagram

Listing 3.7 Bundle stop command

package org.foo.shell;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;

public class StopCommand extends BasicCommand {
public void exec(String id) throws Exception {
Bundle bundle = getBundle(id);
bundle.stop();
}
}
Like starting a bundle, stopping a bundle takes a simple call to Bundle.stop() on the
Bundle object retrieved from the specified identifier. As before, you must be mindful
of the bundle's state. If it's UNINSTALLED , an Illegal-
StateException results. Either STARTING or STOPPING
blocks until ACTIVE or RESOLVED is reached, respec-
tively. In the ACTIVE state, the bundle transitions to
RESOLVED via the STOPPING state. If the bundle has an
activator and the activator's stop() method throws an
exception, a BundleException is thrown. Finally, a
bundle isn't supposed to change its own state; trying to
do so may result in an IllegalStateException .
UPDATE COMMAND
Let's continue with the update command in the follow-
ing listing (see figure 3.11).

Update

Installed

Update

Resolved

Figure 3.11 The update-related
portion of the bundle lifecycle
state diagram