How to convert OutputStream to InputStream?
I am on the stage of development, where I have two modules and from one I got output as a OutputStream and second one, which accepts only InputStream . Do you know how to convert OutputStream to InputStream (not vice versa, I mean really this way) that I will be able to connect these two parts?
Thanks
An OutputStream is one where you write data to. If some module exposes an OutputStream , the expectation is that there is something reading at the other end.
Something that exposes an InputStream , on the other hand, is indicating that you will need to listen to this stream, and there will be data that you can read.
So it is possible to connect an InputStream to an OutputStream
InputStream----read---> intermediateBytes[n] ----write----> OutputStream
As someone metioned, this is what the copy() method from IOUtils lets you do. It does not make sense to go the other way... hopefully this makes some sense
UPDATE:
Of course the more I think of this, the more I can see how this actually would be a requirement. I know some of the comments mentioned Piped input/ouput streams, but there is another possibility.
If the output stream that is exposed is a ByteArrayOutputStream , then you can always get the full contents by calling the toByteArray() method. Then you can create an input stream wrapper by using the ByteArrayInputStream sub-class. These two are pseudo-streams, they both basically just wrap an array of bytes. Using the streams this way, therefore, is technically possible, but to me it is still very strange...
There seem to be many links and other such stuff, but no actual code using pipes. The advantage of using java.io.PipedInputStream and java.io.PipedOutputStream is that there is no additional consumption of memory. ByteArrayOutputStream.toByteArray() returns a copy of the original buffer, so that means that whatever you have in memory, you now have two copies of it. Then writing to an InputStream means you now have three copies of the data.
The code:
// take the copy of the stream and re-write it to an InputStream
PipedInputStream in = new PipedInputStream();
final PipedOutputStream out = new PipedOutputStream(in);
new Thread(new Runnable() {
public void run () {
try {
// write the original OutputStream to the PipedOutputStream
originalByteArrayOutputStream.writeTo(out);
} catch (IOException e) {
// logging and exception handling should go here
}
}
}).start();
This code assumes that the originalByteArrayOutputStream is a ByteArrayOutputStream as it is usually the only usable output stream, unless you're writing to a file. I hope this helps! The great thing about this is that since it's in a separate thread, it also is working in parallel, so whatever is consuming your input stream will be streaming out of your old output stream too. That is beneficial because the buffer can remain smaller and you'll have less latency and less memory usage.
You will need an intermediate class which will buffer between. Each time InputStream.read(byte[]...) is called, the buffering class will fill the passed in byte array with the next chunk passed in from OutputStream.write(byte[]...) . Since the sizes of the chunks may not be the same, the adapter class will need to store a certain amount until it has enough to fill the read buffer and/or be able to store up any buffer overflow.
This article has a nice breakdown of a few different approaches to this problem:
http://blog.ostermiller.org/convert-java-outputstream-inputstream
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