We currently either use the blueprint namespace or the AbstractCommand
and a service definition to define commands. This has some shortcomings:
- The blueprint namespace definition is a bit verbose and at first I did
not understand that actions in the xml can be injected like beans
Example:
<command-bundle xmlns="http://karaf.apache.org/xmlns/shell/v1.1.0";>
<command>
<action class="org.apache.karaf.shell.commands.impl.WatchAction">
<property name="commandProcessor" ref="commandProcessor"/>
</action>
<completers>
<ref component-id="commandCompleter" />
<null/>
</completers>
</command>
</command-bundle>
- The other way using AbstractCommand and a service def is even more
verbose and exposes a lot of implementation details like the
DefaultActionPreparator
<bean id="commandCompleter"
class="org.apache.karaf.shell.console.completer.CommandsCompleter"/>
<service>
<interfaces>
<value>org.apache.felix.service.command.Function</value>
<value>org.apache.karaf.shell.console.CompletableFunction</value>
</interfaces>
<service-properties>
<entry key="osgi.command.scope" value="*"/>
<entry key="osgi.command.function" value="help"/>
</service-properties>
<bean class="org.apache.karaf.shell.console.commands.BlueprintCommand">
<property name="blueprintContainer" ref="blueprintContainer"/>
<property name="blueprintConverter" ref="blueprintConverter"/>
<property name="actionId" value="help"/>
<property name="completers">
<list>
<bean
class="org.apache.karaf.shell.console.completer.CommandNamesCompleter"/>
</list>
</property>
</bean>
</service>
<bean id="help" class="org.apache.karaf.shell.help.impl.HelpAction" activation="lazy"
scope="prototype">
<property name="provider" ref="helpSystem"/>
</bean>
So here is what I propose:
The first thing is to add a complerers property to the @Commands
annotation. This is the last bit we need to make sure the annotations
provide all metadata of an action.
Then the idea is to simply define the action as a blueprint bean and
publish it as an OSGi service. We then have an extender that adapts
these to the felix gogo commands.
So the blueprint code for the help example above would look like:
<service interface="org.apache.karaf.shell.commands.Action">
<bean id="help" class="org.apache.karaf.shell.help.impl.HelpAction"
activation="lazy" scope="prototype">
<property name="provider" ref="helpSystem"/>
</bean>
</service>
With the upcoming blueprint annotations we could simply annotate the
Action class and need no blueprint code at all. The above style would
also work much better with declarative services. If you look at the scr
module in karaf you see how complicated it is till now to create a
command in ds.
One problem with the aproach is of course that the Action has to be
created per execution. So we need to find a good way to clone the Action
object. To a degree this problem is already present int the current
solution.
So what are the advantages:
- The user code only depends on some very few interfaces like Action and
the annotations. AbstractCommand and similar are not needed anymore and
the impls can be private
- The blueprint syntax is quite concise and does not need a special
namespace
- Using BP annotations the syntax is even more concise as no xml is
needed. This would not be possible with the current way
So what do you think?
Christian
--
Christian Schneider
http://www.liquid-reality.de
Open Source Architect
Talend Application Integration Division http://www.talend.com
