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) throws IOException {      try {         // do the compare         while (true) {             int fr = i1.read();             int tr = i2.read();              if (fr != tr)                 return false;              if (fr == -1)                 return true;         }      } finally {         if (i1 != null)             i1.close();         if (i2 != null)             i2.close();     } } 

But it's really slow. I want to use buffered reads but have not come up with a good way of doing it.

Some extra stuff that makes it harder:

• I don't want to read one of the input streams into memory (the whole one)
• I don't want to use a third party library

I need a practial solution - code! :)

Answer 1

By far my favorite is to use the org.apache.commons.io.IOUtils helper class from the Apache Commons IO library:

IOUtils.contentEquals( is1, is2 ); 

Answer 2

Something like this may do:

private static boolean isEqual(InputStream i1, InputStream i2)         throws IOException {      ReadableByteChannel ch1 = Channels.newChannel(i1);     ReadableByteChannel ch2 = Channels.newChannel(i2);      ByteBuffer buf1 = ByteBuffer.allocateDirect(1024);     ByteBuffer buf2 = ByteBuffer.allocateDirect(1024);      try {         while (true) {              int n1 = ch1.read(buf1);             int n2 = ch2.read(buf2);              if (n1 == -1 || n2 == -1) return n1 == n2;              buf1.flip();             buf2.flip();              for (int i = 0; i < Math.min(n1, n2); i++)                 if (buf1.get() != buf2.get())                     return false;              buf1.compact();             buf2.compact();         }      } finally {         if (i1 != null) i1.close();         if (i2 != null) i2.close();     } }