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Subject Proposal: request processing cleanup
Date Thu, 06 Jan 2000 21:30:05 GMT
Existing model

The current request processing is implemented in:

   * ContextManager - it's the entry point used by Adapters ( service()
     method is called after Request/Response is generated).
   * Context - implements the ServletContext API, except mappings.
   * Container - keeps all the mappings defined in context, and all the
   * RequestMapper - implements the alghoritm used to find the servlet
     inside a Container.
   * LookupResult - The servlet associated with a URI, plus path info
     and servlet path
   * RequestDispatcherImpl - will create a new LookupResult and use it
     to create a sub-request
   * InvokerServlet - if no servlet is found in Context/Container, it
     will generate a new one using defaults.
   * DefaultServlet - for non-servlet resources.
   * Request - URI, headers, attributes - and some informations
     generated by the rest of the  code ( overlaps with LookupResult )
   * Interceptors - Context and ServletWrapper will call Lifecycle and
     Service interceptors.

When a request is generated by Adapter, ContextManager will parse the
URI, find the Context and delegate the processing to it.

The Context will delegate it to Container, which will create a new
RequestMapper that will do  a second parsing and return a LookupResult,
and then delegate to the resulted ServletWrapper.  Context and
ServletWrapper will also call a list of Interceptors.

( this is based on my understanding of the code :-)

New model.

This model is based on Interceptors and use the same semantics/alghoritm
as Apache (and NSAPI, ISAPI !!) -  each request ( or sub-request) will
follow the same path,  with several types of Interceptors processing the
request in a specific way.

In addition to the Lifecycle and Service Interceptors ( and the
SecurityInterceptors as defined by J2EE or Craig's security package), we
will have interceptors that will  parse the URI and set the Context,
ServletWrapper and all other informations required by the spec.

   * Request - same role ( changes: move LookupResult functionality
     inside Request, RequestDispatcher will create a subrequest instead
     of using LookupResult )
   * ContextManager - same role, but instead of hardcoded parsing of the
     request to find a Context it will call a a set of translation
     Interceptors == RequestHandlers ( configurable - the current code
     will be the default !).
   * Interceptor ( or RequestHandler ??  ) - will process the request.
     The current parsing code from RequestMapper, ContextManager,
     InvokerServlet, Container, etc will be moved in one or many

The initial implementation will use the existing code to parse the URI
find the Context, ServletWrapper, pathInfo, servletPath, etc and set
in the Request object.

( please also read the Apache docs&code, with Request==request_struct,
ServletWrapper==handler, Context==per_dir_config,  Interceptor=handler
method in a module, etc. )


   * it cleans up existing code. The current code is the result of a
     long evolution ( including the introduction of RequestDispatcher
     and the current semantics of Context), we need something simpler
     and easier to follow.
   * allow better integration with web servers.  This model is similar (
     or identical?) with Apache request processing and few other
   * Will help improve the standalone server - it can use a different
     set of Interceptors, and it is easier to experiment with faster
   * You can customize tomcat for specific tasks. For example, if a
     server has only one context and no virtual hosts it can use a
     simple interceptor and cut 1/2 of the size ( embeded? ). This will
     also fix several virtual-host problems in the existing code.
   * it will keep the critical path in one place, and IMHO it will be
     easier to read and understand.
   * Craig: It is a specific way to process the request - with 2
     Container layers: ContextManager and ServletWrapper. It is a
     particular implementation of Container - it doesn't prevent the
     hierarchy of containers as in your proposal (2.2.1).


I made few experiments and the changes doesn't affect too much outside
Most of the code is written, and assuming no absolute -1 is raised most
code can be reorganized in 1-2 weeks.

The first step is to merge LookupResult and Request, and change
RequestDispatcherImpl and the other classes acordingly. Second,
RequestMapper must be transformed into an Interceptor ( i.e. made
stateless ).

The code from ContextManager can be moved in a Interceptor ( that will
parse the URI and set the Context - if none is already there !).

Some code from Context will go into SessionInterceptor - that will
further decouple the session-related code.

Container.lookupServlet will be part another interceptor ( or merged
with ContextInterceptor, and use same parsing code ).

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