[jetty-dev] Servlet-3.0 WebApp configuration

[Greg Wilkins <gregw@xxxxxxxxxxx>]

All,

the next big refactor that we need to do to the jetty-7/8 code base is
for the webapp configuration mechanism.

The current mechanism consists of a stack of classes for configuring
different aspects of the webapp:

  WEB-INF/lib classloader configuration
  jetty-web.xml
  web.xml
  jetty-env.xml
  tag lib discovery

Some of these are extended by the jetty plus classes to handle
annotations and resource injection.

Without considering servlet-3.0, there are a few problems with
this, mostly that inheritance is not the best way to extend
configurations, you can only have a single inheritance path
and mix and match is thus difficult.

With servlet-3.0 the configuration of a webapplication becomes
even more complex.  We've already hacked in some support for
this, but I'm now thinking we need to take a step back and
redo the entire configuration mechanism.

The non-functional requirements of the configuration mechanism
are:

 + It must be optional and pluggable, so uses such as geronimo
   and jboss can have their own configuration mechanisms.
 + The default needs to be servlet-3.0 compliant
 + It should be easy to take out some features that
   might not be best for production/embedded deployments
   (eg. auto discovery mechanisms etc.).



to fully configure a 3.0 webapp, the process will need to be
something like below.  The key change is that instead of
multiple passes through the configurations - only a single
pass is made, but with each configuration having the
ability to leave data structures for others to work on
  eg. sorted list of jars with fragments
      and effective web.xml parse tree



UnpackConfiguration
-------------------
unpack war file depending on configured
attributes of the webAppContext
Potentially expand WEB-INF/lib/* separately
to avoid jar locking issues.



WebInfConfiguration:
--------------------

 discover WEB-INF/classes and add to class-path

 discover WEB-INF/lib/*.jar  and for each:
   a) add to class-path
   b) scan jar index for
      i)   META-INF/web-fragment.xml
           parse (not process) for name and partial orderings
      ii)  META-INF/*.tld   add to list of tlds
      iii) META-INF/resources add to resource base.

 set Thread context classloader


TempDirConfiguration
--------------------

configure the tempdir location, potentially using a WEB-INF/work directory



WebXmlConfiguration
-------------------

discover defaultweb.xml, WEB-INF/web.xml and override web.xml
   a) parse (but not process) to determine
      i)  if meta-data complete
      ii) if there is a web-fragment ordering

Apply orderings to list of WEB-INF/lib/*.jar
Store list of jars as attribute for later configurations.


Use meta-data-complete and orderings to merge
   * defaultweb.xml
   * web.xml
   * web-fragment.xml s
   * override web.xml

to obtain an effective web.xml that respects
main merging rules.   Store resulting parse
tree as attribute for use by subsequent configuration


process effective web.xml standard configuration


EnvConfiguration
----------------
Process the effective web.xml looking for resources
and other JNDI type stuff.

Process jetty-env.xml



AnnotationConfiguration
-----------------------

For each jar in ordered list scan classes for
   a) handled types for ServletContainerInitializers
   b) Servlets|Filters|Listeners instances with annotations
      i) Setup resource injection for newServlet and newFilter


ContainerInitializerConfiguration
---------------------------------

user JVM service discovery to find ServletContainerInitializer classes
on container classpath.
   a) for each initialize use @HandlesTypes to discover interested classes

For each ServletContainerInitializer
   i) scan ordered jar list for matching classes (or maybe all jars)
   i) call with list of discovered classes and allow to do programmatic
      configuration


TagLibConfiguration
-------------------
Combine list of  META-INF/*.tld with
    * TLDs defined in effective web.xml
    * TLDs discovered in WEB-INF/*.tld (including META-INF/resources/WEB-INF/*.tld)
    Parse TLDs for listeners - add to listener lists.


ListenerConfiguration
---------------------
Call all listeners (which can do programmatic configuration)


LoadOnStartupConfiguration
--------------------------
Sort and instantiate all load-on-startup servlets