Daniel Fagerstrom wrote:
<snip/>
Inter Block Communication
=========================
The servlets (sitemaps) in the different blocks need to be able to call
each other. Also it simplifies reuse of blocks if one block can extend
another one (or rather that a servlets in one block can extend a servlet
in another one). This is achieved with the block protocol.
One way of thinking about the inter block communication is to consider
the servlet in the block to be embedded in an own container where the
the servlets of the other blocks are available through the servlet
context. This is the way I have implemented it, so other servlets can be
called through the getNamedDispatcher method of the servlet context,
with the block name as argument.
The implementation of calls to super blocks and polymorphism requires
the use of a call stack, see [8] for details.
Block properties are accessed as servlet config (and context) init
parameters.
In the OSGi implementation there is a BlockServlet that sets up the the
communication with other blocks and creates the context that the servlet
of the own block is executed within. A declaration of a BlockServlet
might look like:
<scr:component name="cocoon.blockServlet2">
<scr:implementation
class="org.apache.cocoon.blocks.osgi.BlockServlet"/>
<scr:service>
<scr:provide interface="javax.servlet.Servlet"/>
</scr:service>
<scr:property name="path" value="/test2"/>
<scr:property name="attr" value="bar"/>
<scr:reference name="blockServlet"
interface="javax.servlet.Servlet"
target="(component.name=cocoon.servlet2)"/>
<scr:reference name="block1"
interface="javax.servlet.Servlet"
target="(component.name=cocoon.blockServlet1)"/>
</scr:component>
Do I understand correctly that every bundle can have such a component
declaration?
A second question: The bundle provides the interface javax.servlet.Servlet. One
of our goals is polymorphism. What's the plan to achieve this? My idea was
having a declaration like
<scr:component name="fancy-skin">
<scr:implementation class="myCompany.FancySkinServlet"/>
<scr:service>
<scr:provide interface="myCompany.Skin"/>
</scr:service>
<scr:property name="path" value="/test3"/>
</scr:component>
package myCompany;
public interface Skin extends javax.servlet.Servlet {
...
}
A block/bundle that requires my skin could have following declaration:
<scr:component name="myApp">
<scr:implementation
class="org.apache.cocoon.blocks.osgi.BlockServlet"/>
<scr:service>
<scr:provide interface="javax.servlet.Servlet"/>
</scr:service>
<scr:property name="path" value="/test2"/>
<scr:property name="attr" value="bar"/>
<scr:reference name="blockServlet"
interface="javax.servlet.Servlet"
target="(component.name=cocoon.servlet2)"/>
<scr:reference name="skin"
interface="myCompany.FancySkinServlet"
target="(component.name=fancy-skin)"/>
</scr:component>
The target could be overriden by the configuration service. Do we get
polymorphism this way based on the interface of references?
--
Reinhard Pötz Independent Consultant, Trainer & (IT)-Coach
{Software Engineering, Open Source, Web Applications, Apache Cocoon}
web(log): http://www.poetz.cc
--------------------------------------------------------------------
___________________________________________________________
Telefonate ohne weitere Kosten vom PC zum PC: http://messenger.yahoo.de
