How to register hooks into Jetty Startup Lifecycle? - jetty

Question

I am trying to run a piece of code just before a Jetty server starts and stops.
The configuration that starts my server looks similar to this:
public class ExampleServer {
public static void main(String[] args) throws Exception {
Server server = new Server();
ServerConnector connector = new ServerConnector(server);
connector.setPort(8080);
server.setConnectors(new Connector[] { connector });
ServletContextHandler context = new ServletContextHandler();
context.setContextPath("/hello");
context.addServlet(HelloServlet.class, "/");
HandlerCollection handlers = new HandlerCollection();
handlers.setHandlers(new Handler[] { context, new DefaultHandler() });
server.setHandler(handlers);
server.start();
server.join();
}
}
I am not sure what piece of Jetty component I need to configure to be able to insert into the lifecycle.
How do I go about doing this?

Answer 1

The most basic is LifeCycle.Listener which when added to a LifeCycle capable component in the LifeCycle will report the state changes to your own listener.
This will only report for that one component that you have used LifeCycle.addListener(LifeCycle.Listener) on.
Example:
package jetty;
import org.eclipse.jetty.server.Connector;
import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.ServerConnector;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.handler.HandlerCollection;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.util.component.LifeCycle;
public class LifeCycleListenerDemo
{
public static void main(String[] args) throws Exception
{
Server server = new Server();
server.addLifeCycleListener(new CustomLifeCycleListener());
ServerConnector connector = new ServerConnector(server);
connector.setPort(8080);
server.setConnectors(new Connector[] {connector });
ServletContextHandler context = new ServletContextHandler();
context.setContextPath("/hello");
context.addServlet(HelloServlet.class, "/");
HandlerCollection handlers = new HandlerCollection();
handlers.setHandlers(new Handler[] {context, new DefaultHandler() });
server.setHandler(handlers);
server.start();
server.join();
}
public static class CustomLifeCycleListener implements LifeCycle.Listener
{
#Override
public void lifeCycleStarting(LifeCycle event)
{
System.out.println("Starting: " + event);
}
#Override
public void lifeCycleStarted(LifeCycle event)
{
System.out.println("Started: " + event);
}
#Override
public void lifeCycleFailure(LifeCycle event, Throwable cause)
{
System.out.println("Failure: " + event);
cause.printStackTrace(System.out);
}
#Override
public void lifeCycleStopping(LifeCycle event)
{
System.out.println("Stopping: " + event);
}
#Override
public void lifeCycleStopped(LifeCycle event)
{
System.out.println("Stopped: " + event);
}
}
}
There is also a Container.Listener which will tell you about the beans added to a specific container component via ContainerLifeCycle.addEventListener(Container.Listener).
And then there's the specialized Container.InheritedListener which will propagate your Container.InheritedListener to all child beans of the container as well (nested).
You can use this to add your custom LifeCycle.Listener too all registered beans.
Example:
package jetty;
import java.util.HashSet;
import java.util.Set;
import org.eclipse.jetty.server.Connector;
import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.ServerConnector;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.handler.HandlerCollection;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.util.component.Container;
import org.eclipse.jetty.util.component.LifeCycle;
public class LifeCycleNestedListenerDemo
{
public static void main(String[] args) throws Exception
{
Server server = new Server();
CustomLifeCycleListener lifeCycleListener = new CustomLifeCycleListener();
server.addEventListener(lifeCycleListener);
lifeCycleListener.addListener(server); // so we can see server/starting event
ServerConnector connector = new ServerConnector(server);
connector.setPort(8080);
server.setConnectors(new Connector[]{connector});
ServletContextHandler context = new ServletContextHandler();
context.setContextPath("/hello");
context.addServlet(HelloServlet.class, "/");
HandlerCollection handlers = new HandlerCollection();
handlers.setHandlers(new Handler[]{context, new DefaultHandler()});
server.setHandler(handlers);
server.start();
server.join();
}
public static class CustomLifeCycleListener implements Container.InheritedListener, LifeCycle.Listener
{
private Set<Integer> addedObjects = new HashSet<>();
public void addListener(LifeCycle lifeCycle)
{
// identify what we've added the listener too already, so we don't add it multiple times
int identityHashCode = System.identityHashCode(lifeCycle);
if (!addedObjects.contains(identityHashCode))
{
lifeCycle.addLifeCycleListener(this);
addedObjects.add(identityHashCode);
}
}
#Override
public void beanAdded(Container parent, Object child)
{
System.out.printf("beanAdded(%s, %s)%n", parent.getClass().getName(), child.getClass().getName());
if (child instanceof LifeCycle)
{
LifeCycle lifeCycle = (LifeCycle)child;
addListener(lifeCycle);
}
}
#Override
public void beanRemoved(Container parent, Object child)
{
}
#Override
public void lifeCycleStarting(LifeCycle event)
{
System.out.println("Starting: " + event);
}
#Override
public void lifeCycleStarted(LifeCycle event)
{
System.out.println("Started: " + event);
}
#Override
public void lifeCycleFailure(LifeCycle event, Throwable cause)
{
System.out.println("Failure: " + event);
cause.printStackTrace(System.out);
}
#Override
public void lifeCycleStopping(LifeCycle event)
{
System.out.println("Stopping: " + event);
}
#Override
public void lifeCycleStopped(LifeCycle event)
{
System.out.println("Stopped: " + event);
}
}
}