source: nutchez-0.1/tomcat/webapps/docs/architecture/startup/serverStartup.txt @ 112

  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

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