Why doesn't more Java code use PipedInputStream / PipedOutputStream?

Question

I\'ve discovered this idiom recently, and I am wondering if there is something I am missing. I\'ve never seen it used. Nearly all Java code I\'ve worked with in the wild fav

Answer 1

In your example you're creating two threads to do the work that could be done by one. And introducing I/O delays into the mix.

Do you have a better example? Or did I just answer your question.

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To pull some of the comments (at least my view of them) into the main response:

• Concurrency introduces complexity into an application. Instead of dealing with a single linear flow of data, you now have to be concerned about sequencing of independent data flows. In some cases, the added complexity may be justified, particularly if you can leverage multiple cores/CPUs to do CPU-intensive work.
• If you are in a situation where you can benefit from concurrent operations, there's usually a better way to coordinate the flow of data between threads. For example, passing objects between threads using a concurrent queue, rather than wrapping the piped streams in object streams.
• Where a piped stream may be a good solution is when you have multiple threads performing text processing, a la a Unix pipeline (eg: grep | sort).

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In the specific example, the piped stream allows use of an existing RequestEntity implementation class provided by HttpClient. I believe that a better solution is to create a new implementation class, as below, because the example is ultimately a sequential operation that cannot benefit from the complexity and overhead of a concurrent implementation. While I show the RequestEntity as an anonymous class, reusability would indicate that it should be a first-class class.

post.setRequestEntity(new RequestEntity()
{
    public long getContentLength()
    {
        return 0-1;
    }

    public String getContentType()
    {
        return "text/xml";
    }

    public boolean isRepeatable()
    {
        return false;
    }

    public void writeRequest(OutputStream out) throws IOException
    {
        output.setByteStream(out);
        serializer.write(doc, output);
    }
});