Java: Write to OutputStream and then use it as InputStream

Question

I want to get a file from a remote storage as an InputStream without saving it to the local File System. The remote storage provides a Java API with a method that takes an OutputStream and dumps the file data into it.

void dump(OutputStream dest);

The easy way I've come up with is to create a temporary file, dump the data into it and reopen it as an InputStream. But this approach creates a temporary file. Is there an easy way to achieve the same result without a proxy file?

Answer 1

Two options:

Memory

If the "file" in question is small enough for it to be viable, you could read the data into a ByteArrayOutputStream, and then use its toByteArray method to construct a ByteArrayInputStream to read from.

Piping

To avoid storing more in memory than necessary, you could use PipedOutputStream and PipedInputStream.

PipedOutputStream:

A piped output stream can be connected to a piped input stream to create a communications pipe. The piped output stream is the sending end of the pipe. Typically, data is written to a PipedOutputStream object by one thread and data is read from the connected PipedInputStream by some other thread.

PipedInputStream:

A piped input stream should be connected to a piped output stream; the piped input stream then provides whatever data bytes are written to the piped output stream. Typically, data is read from a PipedInputStream object by one thread and data is written to the corresponding PipedOutputStream by some other thread.

You give the API the output stream, and read from the input stream.