Fast way to compare inputstreams

Question

I have a problem, I need to compare two inputstreams fast.

Today I have a function like this:

private boolean isEqual(InputStream i1, InputStream i2) thr         


        

Answer 1

why not simply wrap both streams at the very beginning of your method:

i1 = new BufferedInputStream(i1);
i2 = new BufferedInputStream(i2);

Alternatively, you could simply try reading both streams into a buffer:

public static boolean equals(InputStream i1, InputStream i2, int buf) throws IOException {
    try {
        // do the compare
        while (true) {
            byte[] b1 = new byte[buf];
            byte[] b2 = new byte[buf];

            int length = i1.read(b1);
            if (length == -1) {
                return i2.read(b2, 0, 1) == -1;
            }

            try {
                StreamUtils.readFully(i2, b2, 0, length);
            } catch (EOFException e) {
                // i2 is shorter than i1
                return false;
            }

            if (!ArrayUtils.equals(b1, b2, 0, length)) {
                return false;
            }
        }
    } finally {
        // simply close streams and ignore (log) exceptions
        StreamUtils.close(i1, i2);
    }
}

// StreamUtils.readFully(..) 
public static void readFully(InputStream in, byte[] b, int off, int len) throws EOFException, IOException {
    while (len > 0) {
        int read = in.read(b, off, len);
        if (read == -1) {
            throw new EOFException();
        }
        off += read;
        len -= read;
    }
}

// ArrayUtils.equals(..)
public static boolean equals(byte[] a, byte[] a2, int off, int len) {
    if (off < 0 || len < 0 || len > a.length - off || len > a2.length - off) {
        throw new IndexOutOfBoundsException();
    } else if (len == 0) {
        return true;
    }

    if (a == a2) {
        return true;
    }
    if (a == null || a2 == null) {
        return false;
    }

    for (int i = off; i < off + len; i++) {
        if (a[i] != a2[i]) {
            return false;
        }
    }

    return true;
}

EDIT: I've fixed my implementation now. That's how it looks like without DataInputStream or NIO. Code is available at GitHub or from Sonatype's OSS Snapshot Repository Maven:

  at.molindo
  molindo-utils
  1.0-SNAPSHOT