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/**
<h2>Admin commands in GlassFish</h2>
<h3>Basic Support</h3>
Commands are annotated with {@link org.jvnet.hk2.annotations.Service} annotation and must implement the
{@link org.glassfish.api.admin.AdminCommand} contract. Commands are looked up based on the @Service
{@link org.jvnet.hk2.annotations.Service#name} attribute.
<p>Commands can be singleton or instantiated at each invocation depending on the {@link org.jvnet.hk2.annotations.Scope}
annotation. Singleton commands will be injected once for all {@link org.jvnet.hk2.annotations.Inject} dependencies but
will have all @{link org.glassfish.api.admin.Param} dependencies injected for each invocation.
<p>more to be added to describe the v3 behaviors.
<h3>Supplemental Commands</h3>
A supplemental command is an administrative command that will supplement the execution of an existing command. Although most
supplemental commands can execute in isolation, they usually represent added administrative tasks that can be
optionally installed inside a GlassFish installation and need to be notified when higher level administrative
requests are invoked.
A supplemental command must be annotated with the {@link Supplemental} annotation.
<p>For instance, a supplemental command might configure a particular load-balancer when instances are created or
deleted within a cluster. Usually, this required complicated scripts to first create the instance and then invoke
some subsequent commands to configure the load-balancer. With supplemental commands, the load-balancer supplemental
command can attach itself to the create or delete instance methods and be automatically invoked by the administration
framework when the supplemented command is invoked by the user.
<p>A supplemental command usually run after the supplemented command has finished running successfully. If the
supplemented command fail to execute, none of the supplemental commands should be invoked. A supplemental command can
request to be invoked before the supplemented command. In such a case, these commands must have a
{@link UndoableCommand} annotation to undo any changes in case the supplemented command fail to
execute successfully. If a supplemental command is executing before and does not have {@link Rollbak} annotation, the
system should flag this as an error, and prevent the supplemental method execution.
<p>
It might be possible for a supplemental command to fail executing and since such commands execute usually after the
supplemented command has finished executing, a rollbacking mechanism can be described though the combination of the
{@link org.glassfish.api.admin.ExecuteOn#ifFailure()} annotation value and the {@link UndoableCommand}}. If a clustered
command requires rollbacking when any of its supplemented command fail then it must be annotated with {@link UndoableCommand}
and all of its supplemented commands must also be annotated with {@link UndoableCommand}, otherwise, it must be flagged by
the system as an error.
<p>
Supplemental commands can be a wrapper for existing external commands, and therefore can use a very different set
of parameters than the ones provided to the supplemented command. Supplemental commands can use {@link org.glassfish.api.admin.Supplemental#bridge()}
annotation value to translate or bridge the parameters names and values from the supplemented command to the supplemental
ones.
<p>
<h3>Clustering support</h3>
A command can be optionally annotated with {@link org.glassfish.api.admin.ExecuteOn} to specify the clustering
support. A command not annotated with {@link ExecuteOn} will have a virtual @ExecuteOn annotation with the default values.
(note to asarch, this is mainly for backward compatibility, can be revisited).
<p>A Clustered command will be executed on the server receiving the command from the user (the DAS usually) and any
of the remote instances identified by the {@link org.glassfish.api.admin.ExecuteOn#executor()} instance.
<p>For a command to not be "cluster" available requires the following annotation :
<pre><code>
@ExecuteOn(RuntimeType.DAS)
</code></pre>
<p>Whether commands are executed in parallel or synchronously is immaterial to the user as long as he gets proper
feedback on the remote commands executions successes or failures.
<h3>Rollbacking</h3>
Supplemental and clustered commands execute separately and can create issues when one of the invocation fails.
Commands can optionally implement the {@link UndoableCommand} interface to allow for roll-backing a previously successful
execution of an administrative change.
<p>In a clustering environment, any of the remote invocations can rollback the entire set of changes depending on the
values of {@link org.glassfish.api.admin.ExecuteOn#ifFailure()} and {@link org.glassfish.api.admin.ExecuteOn#ifOffline()}
annotation values.
<p>A Supplemental command can force the roll-backing of the supplemented command using the {@link org.glassfish.api.admin.Supplemental#ifFailure()}
annotation value.
*/