Question

I’m working on a Java web application in which files will be stored in a database. Originally, we retrieved files already in the DB by simply calling getBytes on our result set:

byte[] bytes = resultSet.getBytes(1);
...

This byte array was then converted into a DataHandler using the obvious constructor:

dataHandler = new DataHandler(bytes, "application/octet-stream");

This worked great until we started trying to store and retrieve larger files. Dumping the entire file contents into a byte array and then building a DataHandler out of that simply requires too much memory.

My immediate idea is to retrieve a stream of the data in the database with getBinaryStream and somehow convert that InputStream into a DataHandler in a memory-efficient way. Unfortunately it doesn’t seem like there’s a direct way to convert an InputStream into a DataHandler. Another idea I’ve been playing with is reading chunks of data from the InputStream and writing them to the OutputStream of the DataHandler. But… I can’t find a way to create an "empty" DataHandler that returns a non-null OutputStream when I call getOutputStream…

Has anyone done this? I’d appreciate any help you can give me or leads in the right direction.

Answer 1

My approach would be to write a custom class implementing DataSource that wraps your InputStream. Then create the DataHandler giving it the created DataSource.