Java IO.pdf - Nguyen Dang Binh

}
byte[] result = md.digest();
for (int i = 0; i < result.length; i++) {
System.out.println(result[i]);
}
Java I/O
The main purpose of DigestInputStream is to be one of a chain of filters. Otherwise, it
doesn't really make your work any easier. You still need to construct the MessageDigest
object by invoking getInstance(), pass it to the DigestInputStream() constructor,
retrieve the MessageDigest object from the input stream, invoke its digest() method, and
retrieve the digest data from that object. I would prefer the DigestInputStream to
completely hide the MessageDigest object. You could pass the name of the digest algorithm
to the constructor as a string rather than an actual MessageDigest object. The digest would
only be made available after the stream was closed, and then only through its data, not
through the actual object.
10.3.2 DigestOutputStream
The DigestOutputStream class is a subclass of FilterOutputStream that maintains a digest
of all the bytes it has written:
public class DigestOutputStream extends FilterOutputStream
DigestOutputStream has all the usual methods of any output stream, like write(),
flush(), and close(). It overrides two write() methods to do its filtering:
public void write(int b) throws IOException
public void write(byte[] data, int offset, int length) throws IOException
These are used much as they would be for any other output stream. DigestOutputStream
does not change the data it writes in any way. However, as each byte or group of bytes is
written, it is fed as input to a MessageDigest object stored in the class as the protected
digest field:
protected MessageDigest digest;
This is normally set in the constructor:
public DigestOutputStream(OutputStream out, MessageDigest digest)
For example:
FileOutputStream fout = new FileOutputStream("data.txt");
DigestOutputStream dout = new DigestOutputStream(fout,
MessageDigest.getInstance("SHA"));
The digest is not cloned inside the class. Only a reference to it is stored. Therefore, the
message digest used inside the stream should only be used by the stream. Interleaved use by
other objects or simultaneous use by other threads will corrupt the digest. You can change the
MessageDigest object used by the stream with the setMessageDigest() method:
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