org.arch4j.clientcontroller
Class Transition

java.lang.Object
  |
  +--org.arch4j.clientcontroller.Transition

public abstract class Transition

extends Object

A collection of transitions are specified by each state and driven by the state machine. A transition will handle an event if its guard conditions are met. The transition action leads to a new state.

All deriving transition implementations should have a section of javadoc in the class heading based on the following:

Transition overview

• Event name
• MyEvent
• Context values read by action
• MyReadOnlyValues
• Context values added on action
• MyAddedValues
• Context values updated on action
• MyUpdatedValues
• Context values removed on action
• MyRemovedValues
• Entry condition
• Entry condition description
• Argument values expected on action
• MyExpectedValues
• Resulting states
• MyResultingStates - with descriptions of conditions

Version:

1.0

Author:

David Colwell

Constructor Summary

Transition()
Constructs a Transition object.

Method Summary

abstract State	doAction(Map arguments, StateContext context) Complete any action for the transition and specify a resulting State.
protected Object	getExpectedValueFromArguments(Map arguments, String aKey) Helper method to retrieve an expected value from the argument list.
abstract String	getExternalEvent() Retrieves the name of the external event which this transition reacts to.
protected Object	getValueFromArguments(Map arguments, String aKey) Helper method to retrieve a value from the argument list.
protected boolean	isExternal() Allow the state machine to know if this is an external/internal transition.
abstract boolean	isGuardConditionMet(StateContext context) Checks guard conditions for this transition.
protected void	setAsInternal() Specify that this is an internal transition.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Transition

public Transition()

Constructs a Transition object.

Method Detail

setAsInternal

protected void setAsInternal()

Specify that this is an internal transition. That is, the transition does not change the current state and no exit or entry actions are called.

isExternal

protected boolean isExternal()

Allow the state machine to know if this is an external/internal transition.

getExternalEvent

public abstract String getExternalEvent()

Retrieves the name of the external event which this transition reacts to. If this is specified to be "*", then this Transition will match all events. Note that the guard condition will still be checked and the priority order for registered Transitions is sill valid.

isGuardConditionMet

public abstract boolean isGuardConditionMet(StateContext context)

Checks guard conditions for this transition. Guard conditions allow for event handling based on current context in addition to the event name. However, they are not intended to directly control state. For example, testing a username/password to transition to a logon state should be done in the doAction method which can also specify the logoff state on failure.

Returns:

true if conditions are met, otherwise false.

doAction

public abstract State doAction(Map arguments,
                               StateContext context)
                        throws StateMachineException

Complete any action for the transition and specify a resulting State.

Parameters:

arguments - a list of arguments for the event handler, may be null.

Returns:

the resulting State.

Throws:

StateMachineException - if there is a system related problem processing the request. This might be a missing key-value, application server problems, failed domain validation, or data access errors.

getExpectedValueFromArguments

protected Object getExpectedValueFromArguments(Map arguments,
                                               String aKey)
                                        throws ValueNotFoundException

Helper method to retrieve an expected value from the argument list. If the value doesn't exist it is assumed to be due to a development error.

Returns:

the value, if found.

Throws:

ValueNotFoundException - if the expected key-value is not found in the arguments.

getValueFromArguments

protected Object getValueFromArguments(Map arguments,
                                       String aKey)
                                throws ValueNotFoundException

Helper method to retrieve a value from the argument list.

Returns:

the value, if found, else null.

ValueNotFoundException