Java InputStream to ByteBuffer

A neat solution with no 3rd party library needed is

ByteBuffer byteBuffer = ByteBuffer.allocate(inputStream.available());
Channels.newChannel(inputStream).read(byteBuffer);

See ReadableByteChannel#read(ByteBuffer)

For me the best in this case is Apache commons-io to handle this and similar tasks.

The IOUtils type has a static method to read an InputStream and return a byte[].

InputStream is;
byte[] bytes = IOUtils.toByteArray(is);

Internally this creates a ByteArrayOutputStream and copies the bytes to the output, then calls toByteArray().

UPDATE: as long as you have the byte array, as @Peter pointed, you have to convert to ByteBuffer

ByteBuffer.wrap(bytes)

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JAVA 9 UPDATE: as stated by @saka1029 if you're using java 9+ you can use the default InputStream API which now includes InputStream::readAllBytes function, so no external libraries needed

InputStream is;
byte[] bytes = is.readAllBytes()