Package org.springframework.batch.repeat.support

Class RepeatTemplate

java.lang.Object

org.springframework.batch.repeat.support.RepeatTemplate

All Implemented Interfaces:

RepeatOperations

Direct Known Subclasses:

TaskExecutorRepeatTemplate

public class RepeatTemplate
extends Object
implements RepeatOperations

Simple implementation and base class for batch templates implementing RepeatOperations. Provides a framework including interceptors and policies. Subclasses just need to provide a method that gets the next result and one that waits for all the results to be returned from concurrent processes or threads.
N.B. the template accumulates thrown exceptions during the iteration, and they are all processed together when the main loop ends (i.e. finished processing the items). Clients that do not want to stop execution when an exception is thrown can use a specific CompletionPolicy that does not finish when exceptions are received. This is not the default behaviour.
Clients that want to take some business action when an exception is thrown by the RepeatCallback can consider using a custom RepeatListener instead of trying to customise the CompletionPolicy. This is generally a friendlier interface to implement, and the RepeatListener.after(RepeatContext, RepeatStatus) method is passed in the result of the callback, which would be an instance of Throwable if the business processing had thrown an exception. If the exception is not to be propagated to the caller, then a non-default CompletionPolicy needs to be provided as well, but that could be off the shelf, with the business action implemented only in the interceptor.

Author:

Dave Syer

Field Summary

Fields

Modifier and Type	Field	Description
protected org.apache.commons.logging.Log	logger

Constructor Summary

Constructors

Constructor	Description
RepeatTemplate()

Method Summary

Modifier and Type	Method	Description
protected final boolean	canContinue(RepeatStatus value)	Check return value from batch operation.
protected RepeatInternalState	createInternalState(RepeatContext context)	Create an internal state object that is used to store data needed internally in the scope of an iteration.
protected void	executeAfterInterceptors(RepeatContext context, RepeatStatus value)	Convenience method to execute after interceptors on a callback result.
protected RepeatStatus	getNextResult(RepeatContext context, RepeatCallback callback, RepeatInternalState state)	Get the next completed result, possibly executing several callbacks until one finally finishes.
protected boolean	isComplete(RepeatContext context)	Delegate to CompletionPolicy.
protected boolean	isComplete(RepeatContext context, RepeatStatus result)	Delegate to the CompletionPolicy.
RepeatStatus	iterate(RepeatCallback callback)	Execute the batch callback until the completion policy decides that we are finished.
void	registerListener(RepeatListener listener)	Register an additional listener.
void	setCompletionPolicy(CompletionPolicy terminationPolicy)	Setter for policy to decide when the batch is complete.
void	setExceptionHandler(ExceptionHandler exceptionHandler)	Setter for exception handler strategy.
void	setListeners(RepeatListener[] listeners)	Set the listeners for this template, registering them for callbacks at appropriate times in the iteration.
protected RepeatContext	start()	Delegate to the CompletionPolicy.
protected void	update(RepeatContext context)	Delegate to the CompletionPolicy.
protected boolean	waitForResults(RepeatInternalState state)	If necessary, wait for results to come back from remote or concurrent processes.

Methods inherited from class java.lang.Object

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

Field Details

logger

protected org.apache.commons.logging.Log logger

Constructor Details

RepeatTemplate

public RepeatTemplate()

Method Details

setListeners

public void setListeners(RepeatListener[] listeners)

Set the listeners for this template, registering them for callbacks at appropriate times in the iteration.

Parameters:

listeners - listeners to be used

registerListener

public void registerListener(RepeatListener listener)

Register an additional listener.

Parameters:

listener - a single listener to be added to the list

setExceptionHandler

public void setExceptionHandler(ExceptionHandler exceptionHandler)

Setter for exception handler strategy. The exception handler is called at the end of a batch, after the CompletionPolicy has determined that the batch is complete. By default all exceptions are re-thrown.

Parameters:

exceptionHandler - the ExceptionHandler to use.

See Also:

• ExceptionHandler
• DefaultExceptionHandler
• setCompletionPolicy(CompletionPolicy)

setCompletionPolicy

public void setCompletionPolicy(CompletionPolicy terminationPolicy)

Setter for policy to decide when the batch is complete. The default is to complete normally when the callback returns a RepeatStatus which is not marked as continuable, and abnormally when the callback throws an exception (but the decision to re-throw the exception is deferred to the ExceptionHandler).

Parameters:

terminationPolicy - a TerminationPolicy.

Throws:

IllegalArgumentException - if the argument is null

See Also:

• setExceptionHandler(ExceptionHandler)

iterate

public RepeatStatus iterate(RepeatCallback callback)

Execute the batch callback until the completion policy decides that we are finished. Wait for the whole batch to finish before returning even if the task executor is asynchronous.

Specified by:

iterate in interface RepeatOperations

Parameters:

callback - the batch callback.

Returns:

the aggregate of the result of all the callback operations. An indication of whether the RepeatOperations can continue processing if this method is called again.

See Also:

• RepeatOperations.iterate(org.springframework.batch.repeat.RepeatCallback)

createInternalState

protected RepeatInternalState createInternalState(RepeatContext context)

Create an internal state object that is used to store data needed internally in the scope of an iteration. Used by subclasses to manage the queueing and retrieval of asynchronous results. The default just provides an accumulation of Throwable instances for processing at the end of the batch.

Parameters:

context - the current RepeatContext

Returns:

a RepeatInternalState instance.

See Also:

• waitForResults(RepeatInternalState)

getNextResult

protected RepeatStatus getNextResult(RepeatContext context,
 RepeatCallback callback,
 RepeatInternalState state)
                              throws Throwable

Get the next completed result, possibly executing several callbacks until one finally finishes. Normally a subclass would have to override both this method and createInternalState(RepeatContext) because the implementation of this method would rely on the details of the internal state.

Parameters:

context - current BatchContext.

callback - the callback to execute.

state - maintained by the implementation.

Returns:

a finished result.

Throws:

Throwable - any Throwable emitted during the iteration

See Also:

• isComplete(RepeatContext)
• createInternalState(RepeatContext)

waitForResults

protected boolean waitForResults(RepeatInternalState state)

If necessary, wait for results to come back from remote or concurrent processes. By default does nothing and returns true.

Parameters:

state - the internal state.

Returns:

true if canContinue(RepeatStatus) is true for all results retrieved.

canContinue

protected final boolean canContinue(RepeatStatus value)

Check return value from batch operation.

Parameters:

value - the last callback result.

Returns:

true if the value is RepeatStatus.CONTINUABLE.

executeAfterInterceptors

protected void executeAfterInterceptors(RepeatContext context,
 RepeatStatus value)

Convenience method to execute after interceptors on a callback result.

Parameters:

context - the current batch context.

value - the result of the callback to process.

isComplete

protected boolean isComplete(RepeatContext context,
 RepeatStatus result)

Delegate to the CompletionPolicy.

Parameters:

context - the current batch context.

result - the result of the latest batch item processing.

Returns:

true if complete according to policy and result value, else false.

See Also:

• CompletionPolicy.isComplete(RepeatContext, RepeatStatus)

isComplete

protected boolean isComplete(RepeatContext context)

Delegate to CompletionPolicy.

Parameters:

context - the current batch context.

Returns:

true if complete according to policy alone not including result value, else false.

See Also:

• CompletionPolicy.isComplete(RepeatContext)

start

protected RepeatContext start()

Delegate to the CompletionPolicy.

Returns:

a RepeatContext object that can be used by the implementation to store internal state for a batch step.

See Also:

• CompletionPolicy.start(RepeatContext)

update

protected void update(RepeatContext context)

Delegate to the CompletionPolicy.

Parameters:

context - the value returned by start.

See Also:

• CompletionPolicy.update(RepeatContext)