File Transformers

To transform data read from the file system to objects and the other way around, you need to do some work. Unlike FileReadingMessageSource and to a lesser extent FileWritingMessageHandler, you probably need your own mechanism to get the job done. For this, you can implement the Transformer interface. Alternatively, you can extend the AbstractFilePayloadTransformer for inbound messages. Spring Integration provides some obvious implementations.

See the Javadoc for the Transformer interface to see which Spring Integration classes implement it. Similarly, you can check the Javadoc for the AbstractFilePayloadTransformer class to see which Spring Integration classes extend it.

FileToByteArrayTransformer extends AbstractFilePayloadTransformer and transforms a File object into a byte[] by using Spring’s FileCopyUtils. It is often better to use a sequence of transformers than to put all transformations in a single class. In that case the File to byte[] conversion might be a logical first step.

FileToStringTransformer extends AbstractFilePayloadTransformer convert a File object to a String. If nothing else, this can be useful for debugging (consider using it with a wire tap).

To configure file-specific transformers, you can use the appropriate elements from the file namespace, as the following example shows:

The delete-files option signals to the transformer that it should delete the inbound file after the transformation is complete. This is in no way a replacement for using an AcceptOnceFileListFilter when the FileReadingMessageSource is being used in a multi-threaded environment (such as when you use Spring Integration in general).