Learning lifecycle - OSGi in Action - page 104

public BundleTracker(BundleContext context) {
m_context = context;
m_listener = new SynchronousBundleListener() {
public void bundleChanged(BundleEvent evt) {
synchronized (BundleTracker.this) {
if (!m_open) {
return;
}
if (evt.getType() == BundleEvent.STARTED) {
if (!m_bundleSet.contains(evt.getBundle())) {
m_bundleSet.add(evt.getBundle());
addedBundle(evt.getBundle());
}
} else if (evt.getType() == BundleEvent.STOPPING) {
if (m_bundleSet.contains(evt.getBundle())) {
m_bundleSet.remove(evt.getBundle());
removedBundle(evt.getBundle());
}
}
}
}
};
}
The bundle tracker is constructed with a BundleContext object, which is used to listen
for bundle lifecycle events. The tracker uses a SynchronousBundleListener to listen
to events because a regular BundleListener doesn't get notified when a bundle enters
the STOPPING state, only STOPPED . You need to react on the STOPPING event instead of
the STOPPED event because it's still possible to use the stopping bundle, which hasn't
been stopped yet; a potential subclass might need to do this if it needed to access the
stopping bundle's BundleContext object. The bundle listener's single method B
makes sure the tracker is tracking bundles C . If so, for started events, it adds the asso-
ciated bundle to its bundle list D and invokes the abstract addedBundle() method.
Likewise, for stopping events, it removes the bundle from its bundle list and invokes
the abstract removedBundle() method.
The following listing shows the next portion of the BundleTracker .

B

Implements bundler
listener's method

Checks if tracking
bundles

C

Adds bundle
to list

D

Listing 3.15 Opening and using a BundleTracker

public synchronized void open() {
if (!m_open) {
m_open = true;
m_context.addBundleListener(m_listener);
Bundle[] bundles = m_context.getBundles();
for (int i = 0; i < bundles.length; i++) {
if (bundles[i].getState() == ACTIVE) {
m_bundleSet.add(bundles[i]);
addedBundles(bundles[i]);
}
}
}