net.java.trueupdate.manager.spec.cmd

Interface Command

All Known Implementing Classes:

AbstractCommand, CompositeCommand

public interface Command

An interface for revertible commands with durable side effects. The use case is to compose revertible commands with durable side effects into larger revertible commands with durable side effects.

For example updating an enterprise application in an application may be composed of a list of commands to undeploy, update and redeploy the enterprise application. Each of these commands needs to be revertible so that if for example the final redeployment step fails, the prior update and undeployment steps can get reverted in order. If each of the commands in the list has ACID properties, then this results in the composed command to have ACID properties too, and thus work similar to a transaction.

Note that commands are generally not idempotent, that is once they have been successfully executed, you may not be able to successfully execute them again because the preconditions are no longer met. However, commands must be restartable, that is if perform() has thrown an exception and revert() has succeeded, then clients can still successfully execute the command as soon as the preconditions are met again.

Author:

Christian Schlichtherle

See Also:

Commands.execute(net.java.trueupdate.manager.spec.cmd.Command), CompositeCommand

Method Summary

Modifier and Type	Method and Description
void	perform() Performs this command, thereby creating some durable side effects.
void	revert() Reverts any durable side effects of the perform() method.

Method Detail

perform

void perform()
      throws Exception

Performs this command, thereby creating some durable side effects. If this method throws an exception, then revert() must get called.

Throws:

Exception

revert

void revert()
     throws Exception

Reverts any durable side effects of the perform() method. If this method fails with an exception, then the state of the system may be corrupted.

Throws:

Exception