Using multi-threaded steps in spring batch job

2
votes

I have a spring batch job which takes-in flat file, processes the records and writes-out the output to another flat file. I have used FlatFileItemReader and FlatFileItemWriter as reader and writer respectively. However, when I try to implement multi-threaded steps, my job does not work properly. I get following warnings in my log file

WARN  ChunkMonitor:109 - No ItemReader set (must be concurrent step), so ignoring offset data.
WARN  ChunkMonitor:141 - ItemStream was opened in a different thread.  Restart data could be compromised.

Can you please help me out in implementing multi-threaded step?

1
multithreadingfile-iospring-batch

1 Answers

2
votes

This is because FlatFileItemReader is not thread-safe as the doc says :

/**
 * Abstract superclass for {@link ItemReader}s that supports restart by storing
 * item count in the {@link ExecutionContext} (therefore requires item ordering
 * to be preserved between runs).
 * 
 * Subclasses are inherently *not* thread-safe.
 * 
 * @author Robert Kasanicky
 */

To implements a multi-thread reader, you will have to write a custom reader that synchronize the calls to open and update from the ItemStream interface. If not, your job won't be safe to be restartable.

Hope it helps

Regards