| org.apache.commons.chain.Chain
All known Subclasses: org.apache.commons.chain.impl.ChainBase,
| Chain | | public interface Chain extends Command(Code) | | A
Chain represents a configured list of
Command s that will be executed in order to perform processing
on a specified
Context . Each included
Command will be
executed in turn, until either one of them returns true,
one of the executed
Command s throws an exception,
or the end of the chain has been reached. The
Chain itself will
return the return value of the last
Command that was executed
(if no exception was thrown), or rethrow the thrown exception.
Note that
Chain extends
Command , so that the two can
be used interchangeably when a
Command is expected. This makes it
easy to assemble workflows in a hierarchical manner by combining subchains
into an overall processing chain.
To protect applications from evolution of this interface, specialized
implementations of
Chain should generally be created by extending
the provided base class
org.apache.commons.chain.impl.ChainBase )
rather than directly implementing this interface.
Chain implementations should be designed in a thread-safe
manner, suitable for execution on multiple threads simultaneously. In
general, this implies that the state information identifying which
Command is currently being executed should be maintained in a
local variable inside the execute() method, rather than
in an instance variable. The
Command s in a
Chain may be
configured (via calls to addCommand()) at any time before
the execute() method of the
Chain is first called.
After that, the configuration of the
Chain is frozen.
author:
Craig R. McClanahan
version:
$Revision: 155403 $ $Date: 2005-02-26 12:52:46 +0000 (Sat, 26 Feb 2005) $ |
| Method Summary | |
| void | addCommand(Command command)
Add a
Command to the list of
Command s that will
be called in turn when this
Chain 's execute()
method is called. | | boolean | execute(Context context)
Execute the processing represented by this
Chain according
to the following algorithm.
- If there are no configured
Command s in the
Chain ,
return
false.
- Call the
execute() method of each
Command configured on this chain, in the order they were added via calls
to the addCommand() method, until the end of the
configured
Command s is encountered, or until one of
the executed
Command s returns true
or throws an exception.
- Walk backwards through the
Command s whose
execute() methods, starting with the last one that
was executed. |
| addCommand | | void addCommand(Command command)(Code) | | Add a
Command to the list of
Command s that will
be called in turn when this
Chain 's execute()
method is called. Once execute() has been called
at least once, it is no longer possible to add additional
Command s; instead, an exception will be thrown.
Parameters:
command - The Command to be added
exception:
IllegalArgumentException - if commandis null
exception:
IllegalStateException - if this Chain has alreadybeen executed at least once, so no further configuration is allowed |
| execute | | boolean execute(Context context) throws Exception(Code) | | Execute the processing represented by this
Chain according
to the following algorithm.
- If there are no configured
Command s in the
Chain ,
return
false.
- Call the
execute() method of each
Command configured on this chain, in the order they were added via calls
to the addCommand() method, until the end of the
configured
Command s is encountered, or until one of
the executed
Command s returns true
or throws an exception.
- Walk backwards through the
Command s whose
execute() methods, starting with the last one that
was executed. If this
Command instance is also a
Filter , call its postprocess() method,
discarding any exception that is thrown.
- If the last
Command whose
execute() method
was called threw an exception, rethrow that exception.
- Otherwise, return the value returned by the
execute()
method of the last
Command that was executed. This will be
true if the last
Command indicated that
processing of this
Context has been completed, or
false if none of the called
Command s
returned true.
Parameters:
context - The Context to be processed by thisChain
exception:
Exception - if thrown by one of the Commandsin this Chain but not handled by a postprocess()method of a Filter
exception:
IllegalArgumentException - if contextis null true if the processing of this Contexthas been completed, or false if the processingof this Context should be delegated to a subsequentCommand in an enclosing Chain |
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