cocoon-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Reinhard Poetz (JIRA)" <j...@apache.org>
Subject [jira] Created: (COCOON-1764) Component handling
Date Thu, 02 Feb 2006 22:27:03 GMT
Component handling
------------------

         Key: COCOON-1764
         URL: http://issues.apache.org/jira/browse/COCOON-1764
     Project: Cocoon
        Type: New Feature
  Components: - Blocks Framework  
    Reporter: Reinhard Poetz


see http://marc.theaimsgroup.com/?l=xml-cocoon-dev&m=113813135727508&w=2

In the current implementation of blocks, each block has an own component manager (the choice
of which type is configurable) for managing the components of the block. The block local CM
has an InterBlockServiceManager as parent manager and through it it can access components
from component managers in other blocks that it is *wired* to, (and not from the other blocks
of the system). Let us call this behavior wiring based CM for later reference.

Now I'm starting to think that the above described behavior is unnecessarily complicated and
has some other problems as well. So if no one protests I'm going to change it so that the
blocks still has own component managers, but that they register their (exposed) components
in a global registry and that the parent manager of the local component managers access components
from the global registry and not only from the connected blocks.

Consequences
------------

A global registry is much more similar to the situation in our "compile time" blocks than
the wiring based CM, so it should be easier to migrate, furthermore so is a global registry
used in OSGi so it will be more future safe as well.

A global registry requires less configuration in block.xml and wiring.xml. It is enough to
declare the dependency on the interfaces of the components in the POM. If one want to make
certain that a certain block is used at run time, a run time dependency can declared in the
POM. Connections in the block.xml is only used for declaring inter block servlet communication.

A possible disadvantage is that role names could collide in the global registry but by using
URIs or package names it should be possible to distinguish between components from different
manufacturers.

The global registry approach might give run time errors when components are missing instead
of deploy time errors. But this depends to a large extent on what lookup strategy the components
and the local CMs use. If most of the component lookup is done from within the components
using a service manager the setup problems might be defered to runtime. But if configuration
based dependency injection is used the problems can at least in principle be detected early.

Local vs Global CMs
-------------------

A question that not will matter much until we use OSGi is whether the CMs are used from within
the block or from the outside.

The current design assumes that the CM is internal to each block. The reason for this is that
with OSGi R3 it was, IIUC, the only way to be able to have the implementation classes for
the components internal to the bundle. A global CM would have requried that all implementation
packages to be exported.

With R4 there are some new possibilities, one can get a class loader from a bundle and use
that for constructing components in a global CM. OSGi R4 uses this for the new declarative
services manager. A bundle that want to use the declarative service manager signals that by
pointing out its component declaration with a special manifest header, "Service-Component".
We could have a similar global ECM++ manager for legacy support. It is rather probable that
there will be a OSGi adapted Spring CM, following the same principles.

               --- o0o ---

AFAIR, we haven't discussed what lookup strategy we wanted for components in blocks, I implemented
the wiring based strategy because it seemed more natural for me before. The OSGi CM bridge
that Sylvain implemented used OSGis service registry as a global registry. Gianugo tried to
convince me that global registry was better at ApacheCon, but I was obviously not ready for
it then 

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators:
   http://issues.apache.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see:
   http://www.atlassian.com/software/jira


Mime
View raw message