tomcat-uidm/webapps/docs/architecture/startup/serverStartup.txt

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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 initialize 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 retrieves 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 invocation 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) Invocation of the servlet class