org.springframework.batch.item.support

Class SingleItemPeekableItemReader<T>

java.lang.Object

org.springframework.batch.item.support.SingleItemPeekableItemReader<T>

All Implemented Interfaces:

ItemReader<T>, ItemStream, ItemStreamReader<T>, PeekableItemReader<T>

public class SingleItemPeekableItemReader<T>
extends java.lang.Object
implements ItemStreamReader<T>, PeekableItemReader<T>

A PeekableItemReader that allows the user to peek one item ahead. Repeated calls to peek() will return the same item, and this will be the next item returned from read().

Intentionally not thread-safe: it wouldn't be possible to honour the peek in multiple threads because only one of the threads that peeked would get that item in the next call to read.

Author:

Dave Syer

Constructor Summary

Constructors

Constructor and Description
SingleItemPeekableItemReader()

Method Summary

Modifier and Type	Method and Description
void	close() If the delegate is an ItemStream, just pass the call on, otherwise reset the peek cache.
void	open(ExecutionContext executionContext) If the delegate is an ItemStream, just pass the call on, otherwise reset the peek cache.
T	peek() Peek at the next item, ensuring that if the delegate is an ItemStream the state is stored for the next call to update(ExecutionContext).
T	read() Get the next item from the delegate (whether or not it has already been peeked at).
void	setDelegate(ItemReader<T> delegate) The item reader to use as a delegate.
void	update(ExecutionContext executionContext) If there is a cached peek, then retrieve the execution context state from that point.

Methods inherited from class java.lang.Object

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

Constructor Detail

SingleItemPeekableItemReader

public SingleItemPeekableItemReader()

Method Detail

setDelegate

public void setDelegate(ItemReader<T> delegate)

The item reader to use as a delegate. Items are read from the delegate and passed to the caller in read().

Parameters:

delegate - the delegate to set

read

@Nullable
public T read()
                 throws java.lang.Exception,
                        UnexpectedInputException,
                        ParseException

Get the next item from the delegate (whether or not it has already been peeked at).

Specified by:

read in interface ItemReader<T>

Returns:

T the item to be processed or null if the data source is exhausted

Throws:

ParseException - if there is a problem parsing the current record (but the next one may still be valid)

NonTransientResourceException - if there is a fatal exception in the underlying resource. After throwing this exception implementations should endeavour to return null from subsequent calls to read.

UnexpectedInputException - if there is an uncategorised problem with the input data. Assume potentially transient, so subsequent calls to read might succeed.

java.lang.Exception - if an there is a non-specific error.

See Also:

ItemReader.read()

peek

@Nullable
public T peek()
                 throws java.lang.Exception,
                        UnexpectedInputException,
                        ParseException

Peek at the next item, ensuring that if the delegate is an ItemStream the state is stored for the next call to update(ExecutionContext).

Specified by:

peek in interface PeekableItemReader<T>

Returns:

the next item (or null if there is none).

Throws:

java.lang.Exception - if there is a problem

UnexpectedInputException

ParseException

See Also:

PeekableItemReader.peek()

close

public void close()
           throws ItemStreamException

If the delegate is an ItemStream, just pass the call on, otherwise reset the peek cache.

Specified by:

close in interface ItemStream

Throws:

ItemStreamException - if there is a problem

See Also:

ItemStream.close()

open

public void open(ExecutionContext executionContext)
          throws ItemStreamException

If the delegate is an ItemStream, just pass the call on, otherwise reset the peek cache.

Specified by:

open in interface ItemStream

Parameters:

executionContext - the current context

Throws:

ItemStreamException - if there is a problem

See Also:

ItemStream.open(ExecutionContext)

update

public void update(ExecutionContext executionContext)
            throws ItemStreamException

If there is a cached peek, then retrieve the execution context state from that point. If there is no peek cached, then call directly to the delegate.

Specified by:

update in interface ItemStream

Parameters:

executionContext - the current context

Throws:

ItemStreamException - if there is a problem

See Also:

ItemStream.update(ExecutionContext)