Package org.apache.wiki.workflow

Class Workflow

java.lang.Object
org.apache.wiki.workflow.Workflow
All Implemented Interfaces:
Serializable
public class Workflow
extends Object
implements Serializable

Sequence of Step objects linked together. Workflows are always initialized with a message key that denotes the name of the Workflow, and a Principal that represents its owner.

Workflow lifecycle

A Workflow's state (obtained by getCurrentState()) will be one of the following:

  • CREATED: after the Workflow has been instantiated, but before it has been started using the start() method.
  • RUNNING: after the Workflow has been started using the start() method, but before it has finished processing all Steps. Note that a Workflow can only be started once; attempting to start it again results in an IllegalStateException. Callers can place the Workflow into the WAITING state by calling waitstate().
  • WAITING: when the Workflow has temporarily paused, for example because of a pending Decision. Once the responsible actor decides what to do, the caller can change the Workflow back to the RUNNING state by calling the restart() method (this is done automatically by the Decision class, for instance, when the Decision.decide(Outcome) method is invoked)
  • COMPLETED: after the Workflow has finished processing all Steps, without errors.
  • ABORTED: if a Step has elected to abort the Workflow.

Steps and processing algorithm

Workflow Step objects can be of type Decision, Task or other Step subclasses. Decisions require user input, while Tasks do not. See the Step class for more details.

After instantiating a new Workflow (but before telling it to start()), calling classes should specify the first Step by executing the setFirstStep(Step) method. Additional Steps can be chained by invoking the first step's Step.addSuccessor(Outcome, Step) method.

When a Workflow's start method is invoked, the Workflow retrieves the first Step and processes it. This Step, and subsequent ones, are processed as follows:

  • The Step's Step.start() method executes, which sets the start time.
  • The Step's Step.execute() method is called to begin processing, which will return an Outcome to indicate completion, continuation or errors:
    • Outcome.STEP_COMPLETE indicates that the execution method ran without errors, and that the Step should be considered "completed."
    • Outcome.STEP_CONTINUE indicates that the execution method ran without errors, but that the Step is not "complete" and should be put into the WAITING state.
    • Outcome.STEP_ABORT indicates that the execution method encountered errors, and should abort the Step and the Workflow as a whole. When this happens, the Workflow will set the current Step's Outcome to Outcome.STEP_ABORT and invoke the Workflow's abort() method. The Step's processing errors, if any, can be retrieved by Step.getErrors().
  • The Outcome of the execute method also affects what happens next. Depending on the result (and assuming the Step did not abort), the Workflow will either move on to the next Step or put the Workflow into the WAITING state:
    • If the Outcome denoted "completion" (i.e., its Step.isCompleted() method returns true) then the Step is considered complete; the Workflow looks up the next Step by calling the current Step's Step.getSuccessor(Outcome) method. If successor() returns a non-null Step, the return value is marked as the current Step and added to the Workflow's Step history. If successor() returns null, then the Workflow has no more Steps and it enters the COMPLETED state.
    • If the Outcome did not denote "completion" (i.e., its Step.isCompleted() method returns false), then the Step still has further work to do. The Workflow enters the WAITING state and stops further processing until a caller restarts it.

The currently executing Step can be obtained by getCurrentStep(). The actor for the current Step is returned by getCurrentActor().

To provide flexibility for specific implementations, the Workflow class provides two additional features that enable Workflow participants (i.e., Workflow subclasses and Step/Task/Decision subclasses) to share context and state information. These two features are named attributes and message arguments:

  • Named attributes are simple key-value pairs that Workflow participants can get or set. Keys are Strings; values can be any Object. Named attributes are set with setAttribute(String, Serializable) and retrieved with getAttribute(String).
  • Message arguments are used in combination with JSPWiki's InternationalizationManager to create language-independent user interface messages. The message argument array is retrieved via getMessageArguments(); the first two array elements will always be these: a String representing work flow owner's name, and a String representing the current actor's name. Workflow participants can add to this array by invoking addMessageArgument(Serializable).

Example

Workflow Steps can be very powerful when linked together. JSPWiki provides two abstract subclasses classes that you can use to build your own Workflows: Tasks and Decisions. As noted, Tasks are Steps that execute without user intervention, while Decisions require actors (aka Principals) to take action. Decisions and Tasks can be mixed freely to produce some highly elaborate branching structures.

Here is a simple case. For example, suppose you would like to create a Workflow that (a) executes a initialization Task, (b) pauses to obtain an approval Decision from a user in the Admin group, and if approved, (c) executes a "finish" Task. Here's sample code that illustrates how to do it: 

    // Create workflow; owner is current user
 1  Workflow workflow = new Workflow( " workflow.myworkflow ", context.getCurrentUser() );

    // Create custom initialization task
 2  Step initTask = new InitTask( this );

    // Create finish task
 3  Step finishTask = new FinishTask( this );

    // Create an intermediate decision step
 4  Principal actor = new GroupPrincipal( "Admin" );
 5  Step decision = new SimpleDecision( this, "decision.AdminDecision", actor );

    // Hook the steps together
 6  initTask.addSuccessor( Outcome.STEP_COMPLETE, decision );
 7  decision.addSuccessor( Outcome.DECISION_APPROVE, finishTask );

    // Set workflow's first step
 8  workflow.setFirstStep( initTask );

Some comments on the source code:

  • Line 1 instantiates the workflow with a sample message key and designated owner Principal, in this case the current wiki user
  • Lines 2 and 3 instantiate the custom Task subclasses, which contain the business logic
  • Line 4 creates the relevant GroupPrincipal for the Admin group, who will be the actor in the Decision step
  • Line 5 creates the Decision step, passing the Workflow, sample message key, and actor in the constructor
  • Line 6 specifies that if the InitTask's Outcome signifies "normal completion" (STEP_COMPLETE), the SimpleDecision step should be invoked next
  • Line 7 specifies that if the actor (anyone possessing the Admin GroupPrincipal) selects DECISION_APPROVE, the FinishTask step should be invoked
  • Line 8 adds the InitTask (and all of its successor Steps, nicely wired together) to the workflow
See Also:
Serialized Form

  • Field Summary

    Fields
    Modifier and Type Field Description
    static int ABORTED
    State value: Workflow aborted before completion.
    static int COMPLETED
    State value: Workflow completed all Steps without errors.
    static int CREATED
    State value: Workflow instantiated, but not started.
    static int ID_NOT_SET
    ID value: the workflow ID has not been set.
    static int RUNNING
    State value: Workflow started, and is running.
    static int WAITING
    State value: Workflow paused, typically because a Step returned an Outcome that doesn't signify "completion."

  • Constructor Summary

    Constructors
    Constructor Description
    Workflow​(String messageKey, Principal owner)
    Constructs a new Workflow object with a supplied message key, owner Principal, and undefined unique identifier ID_NOT_SET.

  • Method Summary

    Modifier and Type Method Description
    void abort()
    Aborts the Workflow by setting the current Step's Outcome to Outcome.STEP_ABORT, and the Workflow's overall state to ABORTED.
    void addMessageArgument​(Serializable obj)
    Appends a message argument object to the array returned by getMessageArguments().
    protected void cleanup()
    Clears the attribute map and sets the current step field to null.
    protected void complete()
    Protected helper method that changes the Workflow's state to COMPLETED and sets the current Step to null.
    Object getAttribute​(String attr)
    Retrieves a named Object associated with this Workflow.
    Map<String,​Serializable> getAttributes()
    Retrieves workflow's attributes.
    Principal getCurrentActor()
    Returns the actor Principal responsible for the current Step.
    int getCurrentState()
    Returns the workflow state: CREATED, RUNNING, WAITING, COMPLETED or ABORTED.
    Step getCurrentStep()
    Returns the current Step, or null if the workflow has not started or already completed.
    Date getEndTime()
    The end time for this Workflow, expressed as a system time number.
    List<Step> getHistory()
    Returns a Step history for this Workflow as a List, chronologically, from the first Step to the currently executing one.
    int getId()
    Returns the unique identifier for this Workflow.
    Serializable[] getMessageArguments()
    Returns an array of message arguments, used by MessageFormat to create localized messages.
    String getMessageKey()
    Returns an i18n message key for the name of this workflow; for example, workflow.saveWikiPage.
    Principal getOwner()
    The owner Principal on whose behalf this Workflow is being executed; that is, the user who created the workflow.
    Step getPreviousStep()
    Convenience method that returns the predecessor of the current Step.
    Date getStartTime()
    The start time for this Workflow, expressed as a system time number.
    boolean isAborted()
    Returns true if the workflow had been previously aborted.
    boolean isCompleted()
    Determines whether this Workflow is completed; that is, if it has no additional Steps to perform.
    boolean isStarted()
    Determines whether this Workflow has started; that is, its start() method has been executed.
    protected Step previousStep​(Step step)
    Protected method that returns the predecessor for a supplied Step.
    protected void processCurrentStep()
    Protected method that processes the current Step by calling Step.execute().
    void restart()
    Restarts the Workflow from the WAITING state and puts it into the RUNNING state again.
    void setAttribute​(String attr, Serializable obj)
    Temporarily associates an object with this Workflow, as a named attribute, for the duration of workflow execution.
    void setFirstStep​(Step step)
    Sets the first Step for this Workflow, which will be executed immediately after the start() method executes.
    void setId​(int id)
    Sets the unique identifier for this Workflow.
    void start()
    Starts the Workflow and sets the state to RUNNING.
    void waitstate()
    Sets the Workflow in the WAITING state.

    Methods inherited from class java.lang.Object

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

  • Field Details

  • Constructor Details

    • Workflow

      public Workflow​(String messageKey, Principal owner)
      Constructs a new Workflow object with a supplied message key, owner Principal, and undefined unique identifier ID_NOT_SET. Once instantiated the Workflow is considered to be in the CREATED state; a caller must explicitly invoke the start() method to begin processing.
      Parameters:
      messageKey - the message key used to construct a localized workflow name, such as workflow.saveWikiPage
      owner - the Principal who owns the Workflow. Typically, this is the user who created and submitted it

  • Method Details

    • abort

      public final void abort()
      Aborts the Workflow by setting the current Step's Outcome to Outcome.STEP_ABORT, and the Workflow's overall state to ABORTED. It also appends the aborted Step into the workflow history, and sets the current step to null. If the Step is a Decision, it is removed from the DecisionQueue. This method can be called at any point in the lifecycle prior to completion, but it cannot be called twice. It finishes by calling the cleanup() method to flush retained objects. If the Workflow had been previously aborted, this method throws an IllegalStateException.

    • addMessageArgument

      public final void addMessageArgument​(Serializable obj)
      Appends a message argument object to the array returned by getMessageArguments(). The object must be an type used by the MessageFormat: String, Date, or Number (BigDecimal, BigInteger, Byte, Double, Float, Integer, Long, Short). If the object is not of type String, Number or Date, this method throws an IllegalArgumentException.
      Parameters:
      obj - the object to add

    • getCurrentActor

      public final Principal getCurrentActor()
      Returns the actor Principal responsible for the current Step. If there is no current Step, this method returns null.
      Returns:
      the current actor

    • getCurrentState

      public final int getCurrentState()
      Returns the workflow state: CREATED, RUNNING, WAITING, COMPLETED or ABORTED.
      Returns:
      the workflow state

    • getCurrentStep

      public final Step getCurrentStep()
      Returns the current Step, or null if the workflow has not started or already completed.
      Returns:
      the current step

    • getAttribute

      public final Object getAttribute​(String attr)
      Retrieves a named Object associated with this Workflow. If the Workflow has completed or aborted, this method always returns null.
      Parameters:
      attr - the name of the attribute
      Returns:
      the value

    • getAttributes

      public final Map<String,​Serializable> getAttributes()
      Retrieves workflow's attributes.
      Returns:
      workflow's attributes.

    • getEndTime

      public final Date getEndTime()
      The end time for this Workflow, expressed as a system time number. This value is equal to the end-time value returned by the final Step's Step.getEndTime() method, if the workflow has completed. Otherwise, this method returns Step.TIME_NOT_SET.
      Returns:
      the end time

    • getId

      public final int getId()
      Returns the unique identifier for this Workflow. If not set, this method returns ID_NOT_SET (0).
      Returns:
      the unique identifier

    • getMessageArguments

      public final Serializable[] getMessageArguments()

      Returns an array of message arguments, used by MessageFormat to create localized messages. The first two array elements will always be these:

      • String representing the name of the workflow owner (i.e.,getOwner())
      • String representing the name of the current actor (i.e.,getCurrentActor()). If the current step is null because the workflow hasn't started or has already finished, the value of this argument will be a dash character (-)

      Workflow and Step subclasses are free to append items to this collection with addMessageArgument(Serializable).

      Returns:
      the array of message arguments

    • getMessageKey

      public final String getMessageKey()
      Returns an i18n message key for the name of this workflow; for example, workflow.saveWikiPage.
      Returns:
      the name

    • getOwner

      public final Principal getOwner()
      The owner Principal on whose behalf this Workflow is being executed; that is, the user who created the workflow.
      Returns:
      the name of the Principal who owns this workflow

    • getStartTime

      public final Date getStartTime()
      The start time for this Workflow, expressed as a system time number. This value is equal to the start-time value returned by the first Step's Step.getStartTime() method, if the workflow has started already. Otherwise, this method returns Step.TIME_NOT_SET.
      Returns:
      the start time

    • getHistory

      public final List<Step> getHistory()
      Returns a Step history for this Workflow as a List, chronologically, from the first Step to the currently executing one. The first step is the first item in the array. If the Workflow has not started, this method returns a zero-length array.
      Returns:
      an array of Steps representing those that have executed, or are currently executing

    • isAborted

      public final boolean isAborted()
      Returns true if the workflow had been previously aborted.
      Returns:
      the result

    • isCompleted

      public final boolean isCompleted()
      Determines whether this Workflow is completed; that is, if it has no additional Steps to perform. If the last Step in the workflow is finished, this method will return true.
      Returns:
      true if the workflow has been started but has no more steps to perform; false if not.

    • isStarted

      public final boolean isStarted()
      Determines whether this Workflow has started; that is, its start() method has been executed.
      Returns:
      true if the workflow has been started; false if not.

    • getPreviousStep

      public final Step getPreviousStep()
      Convenience method that returns the predecessor of the current Step. This method simply examines the Workflow history and returns the second-to-last Step.
      Returns:
      the predecessor, or null if the first Step is currently executing

    • restart

      public final void restart() throws WikiException
      Restarts the Workflow from the WAITING state and puts it into the RUNNING state again. If the Workflow had not previously been paused, this method throws an IllegalStateException. If any of the Steps in this Workflow throw a WikiException, the Workflow will abort and propagate the exception to callers.
      Throws:
      WikiException - if the current task's AbstractStep.execute() method throws an exception

    • setAttribute

      public final void setAttribute​(String attr, Serializable obj)
      Temporarily associates an object with this Workflow, as a named attribute, for the duration of workflow execution. The passed object can be anything required by an executing Step, although it should be serializable. Note that when the workflow completes or aborts, all attributes will be cleared.
      Parameters:
      attr - the attribute name
      obj - the value

    • setFirstStep

      public final void setFirstStep​(Step step)
      Sets the first Step for this Workflow, which will be executed immediately after the start() method executes. Note than the Step is not marked as the "current" step or added to the Workflow history until the start() method is called.
      Parameters:
      step - the first step for the workflow

    • setId

      public final void setId​(int id)
      Sets the unique identifier for this Workflow.
      Parameters:
      id - the unique identifier

    • start

      public final void start() throws WikiException
      Starts the Workflow and sets the state to RUNNING. If the Workflow has already been started (or previously aborted), this method returns an IllegalStateException. If any of the Steps in this Workflow throw a WikiException, the Workflow will abort and propagate the exception to callers.
      Throws:
      WikiException - if the current Step's Step.start() method throws an exception of any kind

    • waitstate

      public final void waitstate()
      Sets the Workflow in the WAITING state. If the Workflow is not running or has already been paused, this method throws an IllegalStateException. Once paused, the Workflow can be un-paused by executing the restart() method.

    • cleanup

      protected void cleanup()
      Clears the attribute map and sets the current step field to null.

    • complete

      protected final void complete()
      Protected helper method that changes the Workflow's state to COMPLETED and sets the current Step to null. It calls the cleanup() method to flush retained objects. This method will no-op if it has previously been called.

    • previousStep

      protected final Step previousStep​(Step step)
      Protected method that returns the predecessor for a supplied Step.
      Parameters:
      step - the Step for which the predecessor is requested
      Returns:
      its predecessor, or null if the first Step was supplied.

    • processCurrentStep

      protected final void processCurrentStep() throws WikiException
      Protected method that processes the current Step by calling Step.execute(). If the execute throws an exception, this method will propagate the exception immediately to callers without aborting.
      Throws:
      WikiException - if the current Step's Step.start() method throws an exception of any kind