This sample demonstrates how to wire a message flow to process Files sequentially (maintain the order) or concurrently (no order). The difference is in the Poller configuration - single threaded or multi-threaded.
The Poller, configured for the File Inbound Channel Adapter and after polling files and converting them to Messages, will distribute these Messages one at the time using its own thread by default. So files will be pulled based in the order they were created in the directory and processed in such order.
See sequentialFileProcessing-config.xml for configuration details. The FileProcessor class will randomly delay the file processing, but the order of processing is still maintained regardless of this delay.
If order is not important, then you can process files concurrently. All you need to do, is to configure a task-executor for the Poller. Based on the delay in FileProcessor, you'll clearly observe that the order of processing is based on the availability of the thread in the thread poll of task executor
To run sample, execute FileProcessingTest. You should see the following output:
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest -
#### Starting Sequential processing test ####
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Populating directory with files
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Populated directory with files
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Starting Spring Integration Sequential File processing
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_0.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_0.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_1.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_1.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_2.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_2.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_3.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_3.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_4.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_4.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest -
#### Starting Concurrent processing test ####
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Populating directory with files
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Populated directory with files
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Starting Spring Integration Sequential File processing
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_1.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_1.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_0.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_0.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_3.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_3.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_4.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_4.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessor - Processing File: input/file_2.txt
INFO : org.springframework.integration.samples.fileprocessing.FileProcessingTest - Finished processing input/file_2.txt unless you specify task-executor or introduce task-executor somewhere downstream you are fine.