Memory Stream in Java

Question

ByteArrayInputStream and ByteArrayOutputStream is what you are looking for.

These are implementations of the interfaces InputStream and OutputStream that read from and write to a byte array in memory. For ByteArrayOutputStream, the array will grow automatically as you write data to the stream.

Does it need to support the Input and Output Streams? If not I would just use a ByteBuffer which allows you to read/write primitive types at random locations. (Up to 2 GB)

You can share a ByteBuffer between a reader and a writer.

e.g.

// 1 GB of virtual memory outside the heap.
ByteBuffer writer = ByteBuffer.allocateDirect(1024*1024*1024); 
ByteBuffer reader = writer.slice();

You can share memory between threads (e.g. Exchanger) and processes (using memory mapped files)

You can use PipedInputStream and PipedOutputStream

like this:

PipedOutputStream outstr = new PipedOutputStream();
PipedInputStream instr = new PipedInputStream(outstr);

that won't directly allow you to seek, but it does allow you to skip as many bytes you want from the input stream.

Be aware that whenever you write into the outstr it is blocked until everything is read from in instr (that is: if I remember correctly the Streams don't Buffer, but you can decorate them with a BufferedInputStream then you don't have to bother.

NIO allows you to directly transfer data within kernel memory - I'm not sure if it exactly overlaps with .NET's memory stream. Here's a simple example of mapping an entire file into memory for reading.