Read all standard input into a Java byte array

问题:

What's the simplest way in modern Java (using only the standard libraries) to read all of standard input until EOF into a byte array, preferably without having to provide that array oneself? The stdin data is binary stuff and doesn't come from a file.

I.e. something like Ruby's

foo = $stdin.read

The only partial solution I could think of was along the lines of

byte[] buf = new byte[1000000];
int b;
int i = 0;

while (true) {
    b = System.in.read();
    if (b == -1)
        break;
    buf[i++] = (byte) b;
}

byte[] foo[i] = Arrays.copyOfRange(buf, 0, i);

... but that seems bizarrely verbose even for Java, and uses a fixed size buffer.

回答1:

I'd use Guava and its ByteStreams.toByteArray method:

byte[] data = ByteStreams.toByteArray(System.in);

Without using any 3rd party libraries, I'd use a ByteArrayOutputStream and a temporary buffer:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buffer = new byte[32 * 1024];

int bytesRead;
while ((bytesRead = System.in.read(buffer)) > 0) {
    baos.write(buffer, 0, bytesRead);
}
byte[] bytes = baos.toByteArray();

... possibly encapsulating that in a method accepting an InputStream, which would then be basically equivalent to ByteStreams.toByteArray anyway...

回答2:

If you're reading from a file, Files.readAllBytes is the way to do it.

Otherwise, I'd use a ByteBuffer:

ByteBuffer buf = ByteBuffer.allocate(1000000);
ReadableByteChannel channel = Channels.newChannel(System.in);
while (channel.read(buf) >= 0)
    ;
buf.flip();
byte[] bytes = Arrays.copyOf(buf.array(), buf.limit());