Adding characters to beginning and end of InputStream in Java

Question

I have an InputStream which I need to add characters to the beginning and end of, and should end up with another variable of type InputStream. How could I easily do this?

Solution

You want a SequenceInputStream and a couple of ByteArrayInputStreams. You can use String.getBytes to make the bytes for the latter. SequenceInputStream is ancient, so it's a little clunky to use:

InputStream middle ;
String beginning = "Once upon a time ...\n";
String end = "\n... and they lived happily ever after.";
List<InputStream> streams = Arrays.asList(
    new ByteArrayInputStream(beginning.getBytes()),
    middle,
    new ByteArrayInputStream(end.getBytes()));
InputStream story = new SequenceInputStream(Collections.enumeration(streams));

If you have a lot of characters to add, and don't want to convert them to bytes en masse, you could put them in a StringReader, then use a ReaderInputStream from Commons IO to read them as bytes. But you would need to add Commons IO to your project to do that. Exact code for that is left as an exercise for the reader.

Comments

[pqn]

More detail please? Thanks for the handy class names.

[Tom Anderson]

How do you write characters to an InputStream?

[Alex]

-1, Write the ending characters to your new InputStream. -> you can't write characters to an InputStream

[JB Nizet]

If you read the javadoc for those classes, it's pretty obvious. Construct a first ByteArrayInputStream (let's call it head) containing the bytes of the beginning, a second one containing the bytes of the end (let's call it tail), and build a SequenceInputStream from the head, the original input stream, and the tail.

[rossum]

Whoops! Reboots brain. Write to an output stream, backed by a byte array as Greg says. Extract the backing array and reopen as an input stream. Thanks for the correction.

[pqn]

Also, it should be Arrays.asList and not Collections.asList.

[Fabian Tamp]

-1, this would've been better represented with code and isn't efficient for large streams.

[rossum]

@Fabian I read this question as homework, hence I gave help, but not code. YMMV.