javainputstream

Reading a binary input stream into a single byte array in Java

The documentation says that one should not use available() method to determine the size of an InputStream. How can I read the whole content of an InputStream into a byte array?

InputStream in; //assuming already present
byte[] data = new byte[in.available()];
in.read(data);//now data is filled with the whole content of the InputStream

I could read multiple times into a buffer of a fixed size, but then, I will have to combine the data I read into a single byte array, which is a problem for me.

Solution

  • The simplest approach IMO is to use Guava and its ByteStreams class:

    byte[] bytes = ByteStreams.toByteArray(in);

    Or for a file:

    byte[] bytes = Files.toByteArray(file);

    Alternatively (if you didn't want to use Guava), you could create a ByteArrayOutputStream, and repeatedly read into a byte array and write into the ByteArrayOutputStream (letting that handle resizing), then call ByteArrayOutputStream.toByteArray().

    Note that this approach works whether you can tell the length of your input or not - assuming you have enough memory, of course.