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NIO Stream Storage

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The NIO Stream Storage project is a lightweight library to store streamed byte data and read them back. The core component, StreamStorage (which extends OutputStream) is used as the destination to write incoming bytes as they are available. The StreamStorage is required to supply an InputStream of the stored bytes when requested. The StreamStorage is implementing the Disposable interface for automatic resource management.

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The default implementation of StreamStorage provided by the library is the FileStreamStorage. The implementation enforces two distinct states:

  • The StreamStorage is ONLY writable and NOT readable.
  • The StreamStorage is ONLY readable and NOT writable.

A new instance will always start in a write state, ready to accept bytes and any call to the getInputStream() will fail. Once all the data has been written, the close() method needs to be called to close the write channel and switch the FileStreamStorage to the read state.

Additionally, the FileStreamStorage can be configured to:

  • Use a combination of in memory and file storage. In fact a memory threshold can be set and the bytes will be kept in memory until the threshold is reached. Once the threshold is reached, the FileStreamStorage will flush the in memory data to file and it will keep writing directly to that file.
  • Delete the underlying file after the FileStreamStorage is disposed.
  • Delete the underlying file after the InputStream supplied by the FileStreamStorage is closed.
  • Append the data to the underlying file. This option is only available when the threshold is set to 0 and it is made available to support scenarios where the write needs to be resumed.
  • Enforce a capacity limit. Exceeding the capacity will result in an error (IllegalStateException)


Instantiate a StreamStorage object either directly or via a configured Factory:

StreamStorageFactory streamStorageFactory = new DeferredFileStreamStorageFactory();
// Coinfigure the streamStorageFactory if needed
StreamStorage streamStorage = streamStorageFactory.create();

StreamStorage is an OutputStream so simply write bytes to it and close the stream once complete:

streamStorage.write(new byte[]{0x03, 0x4, 0x5});
streamStorage.write(new byte[]{0x01, 0x02});

Retrieve an InputStream of the stored bytes:

InputStream inputStream = streamStorage.getInputStream();

Close the InputStream to cleanup the underlying file:


Advanced Configuration

It is possible to configure an in-memory threshold before storing data on disk. If configured the data is flushed to disk only if that in-memory threshold is reached. This is provided as a potential optimisation to avoid unnecessary slow disk IO. It should be noted however that even without this option (when flushing directly to disk) there will likely be a Page Cache hit on the OS anyway, especially if the lifecycle of StreamStorage is relatively short-lived. So it may be worth bench-marking any use of this in-memory threshold.