Tomcat 5 Startup Sequence



Sequence 1. Start from Command Line

Class: org.apache.catalina.startup.Bootstrap

What it does:

	a) Set up classloaders 

		commonLoader (common)-> System Loader

		sharedLoader (shared)-> commonLoader -> System Loader

		catalinaLoader(server) -> commonLoader -> System Loader

	b) Load startup class (reflection)

		org.apache.catalina.startup.Catalina

		setParentClassloader -> sharedLoader

		Thread.contextClassloader -> catalinaLoader

	c) Bootstrap.daemon.init() complete

	

Sequence 2. Process command line argument (start, startd, stop, stopd)

Class: org.apache.catalina.startup.Bootstrap (assume command->start)

What it does: 

	a) Catalina.setAwait(true);

	b) Catalina.load()

		b1) initDirs() -> set properties like 

		                  catalina.home

		                  catalina.base == catalina.home (most cases)

		b2) initNaming

			setProperty(javax.naming.Context.INITIAL_CONTEXT_FACTORY,

				    org.apache.naming.java.javaURLContextFactory ->default)

		b3) createStartDigester() 

			Configures a digester for the main server.xml elements like

			org.apache.catalina.core.StandardServer (can change of course :)

			org.apache.catalina.deploy.NamingResources

				Stores naming resources in the J2EE JNDI tree

			org.apache.catalina.LifecycleListener

				implements events for start/stop of major components

			org.apache.catalina.core.StandardService

				The single entry for a set of connectors,

				so that a container can listen to multiple connectors

				ie, single entry

			org.apache.coyote.tomcat5.CoyoteConnector

				Connectors to listen for incoming requests only

			It also adds the following rulesets to the digester

				NamingRuleSet

				EngineRuleSet

				HostRuleSet

				ContextRuleSet

		b4) Load the server.xml and parse it using the digester

		    Parsing the server.xml using the digester is an automatic

		    XML-object mapping tool, that will create the objects defined in server.xml

		    Startup of the actual container has not started yet.

		b5) Assigns System.out and System.err to the SystemLogHandler class

		b6) Calls intialize on all components, this makes each object register itself with the 

		    JMX agent.

		    During the process call the Connectors also initialize the adapters.

		    The adapters are the components that do the request pre-processing.

		    Typical adapters are HTTP1.1 (default if no protocol is specified,

		    org.apache.coyote.http11.Http11Protocol)

		    AJP1.3 for mod_jk etc.



	c) Catalina.start()

		c1) Starts the NamingContext and binds all JNDI references into it

		c2) Starts the services under <Server> which are:

			StandardService -> starts Engine (ContainerBase ->Logger,Loader,Realm,Cluster etc)

		c3) StandardHost (started by the service)

				Configures a ErrorReportValvem to do proper HTML output for different HTTP 

				errors codes

				Starts the Valves in the pipeline (at least the ErrorReportValve)

				Configures the StandardHostValve, 

					this valves ties the Webapp Class loader to the thread context

					it also finds the session for the request

					and invokes the context pipeline

				Starts the HostConfig component

					This component deploys all the webapps

						(webapps & conf/Catalina/localhost/*.xml)

					Webapps are installed using the deployer (StandardHostDeployer)

					The deployer will create a Digester for your context, this digester

					will then invoke ContextConfig.start()

						The ContextConfig.start() will process the default web.xml (conf/web.xml)

						and then process the applications web.xml (WEB-INF/web.xml)

						

		c4) During the lifetime of the container (StandardEngine) there is a background thread that 

		    keeps checking if the context has changed. If a context changes (timestamp of war file, 

		    context xml file, web.xml) then a reload is issued (stop/remove/deploy/start)

		    

	d) Tomcat receives a request on an HTTP port

	    d1) The request is received by a separate thread which is waiting in the PoolTcpEndPoint 

	         class. It is waiting for a request in a regular ServerSocket.accept() method.

	         When a request is received, this thread wakes up.

	    d2) The PoolTcpEndPoint assigns the a TcpConnection to handle the request. 

	        It also supplies a JMX object name to the catalina container (not used I believe)

	    d3) The processor to handle the request in this case is Coyote Http11Processor, 

	        and the process method is invoked.

	        This same processor is also continuing to check the input stream of the socket

	        until the keep alive point is reached or the connection is disconnected.

	    d4) The HTTP request is parsed using an internal buffer class (Coyote Http11 Internal Buffer)

	        The buffer class parses the request line, the headers, etc and store the result in a 

	        Coyote request (not an HTTP request) This request contains all the HTTP info, such

	        as servername, port, scheme, etc.

	    d5) The processor contains a reference to an Adapter, in this case it is the 

	        Coyote Tomcat 5 Adapter. Once the request has been parsed, the Http11 processor

	        invokes service() on the adapter. In the service method, the Request contains a 

	        CoyoteRequest and CoyoteRespons (null for the first time)

	        The CoyoteRequest(Response) implements HttpRequest(Response) and HttpServletRequest(Response)

	        The adapter parses and associates everything with the request, cookies, the context through a 

	        Mapper, etc

	    d6) When the parsing is finished, the CoyoteAdapter invokes its container (StandardEngine)

	        and invokes the invoke(request,response) method.

	        This initiates the HTTP request into the Catalina container starting at the engine level

	    d7) The StandardEngine.invoke() simply invokes the container pipeline.invoke()

	    d8) By default the engine only has one valve the StandardEngineValve, this valve simply

	        invokes the invoke() method on the Host pipeline (StandardHost.getPipeLine())

	    d9) the StandardHost has two valves by default, the StandardHostValve and the ErrorReportValve

	    d10) The standard host valve associates the correct class loader with the current thread

	         It also retrives the Manager and the session associated with the request (if there is one)

	         If there is a session access() is called to keep the session alive

	    d11) After that the StandardHostValve invokes the pipeline on the context associated

	         with the request.

	    d12) The first valve that gets invoked by the Context pipeline is the FormAuthenticator

	         valve. Then the StandardContextValve gets invoke.

	         The StandardContextValve invokes any context listeners associated with the context.

	         Next it invokes the pipeline on the Wrapper component (StandardWrapperValve)

	    d13) During the invokation of the StandardWrapperValve, the JSP wrapper (Jasper) gets invoked

	         This results in the actual compilation of the JSP.

	         And then invokes the actual servlet.

	e) Invokation of the servlet class

	         

	         

	         

	    

	        

	        

	        

	    

			

			

		

		

			