Java IO.pdf - Nguyen Dang Binh

}
}
catch (MalformedURLException e) {System.err.println(e);}
catch (Exception e) {System.err.println(e);}
public static byte[] getDigestFromURL(URL u)
throws IOException, NoSuchAlgorithmException {
}
MessageDigest sha = MessageDigest.getInstance("MD5");
InputStream in = u.openStream();
byte[] data = new byte[128];
while (true) {
int bytesRead = in.read(data);
if (bytesRead < 0) { // end of stream
break;
}
sha.update(data, 0, bytesRead);
}
return sha.digest();
Here's a sample run:
% java TrueMirror http://metalab.unc.edu/javafaq/
http://sunsite.uakom.sk/javafaq/
http://metalab.uakom.sk/javafaq/ is up to date
10.2.7 Accessor Methods
Java I/O
The MessageDigest class contains three accessor methods that return information about the
digest:
public final Provider getProvider()
public final String getAlgorithm()
public final int getDigestLength()
The getProvider() method returns a reference to the instance of java.security.Provider
that provided this MessageDigest implementation. The getAlgorithm() method returns a
string containing the name of the digest algorithm as given in Table 10.1; for example, "SHA"
or "MD2". Finally, getDigestLength()returns the length of the digest in bytes. Digest
algorithms are supposed to have fixed lengths. For instance, SHA digests are always 20 bytes
long. However, this method allows for the possibility of variable length digests. It returns if
the length of the digest is not yet available.
10.2.8 Cloning Digests
Some digests allow themselves to be cloned, though not all do. A digest that does not
implement cloning throws a CloneNotSupportedException if you attempt to clone it. SHA
and MD5 digests from the JDK do support cloning. Cloning a digest is useful if you want to
view a series of intermediate digests before the entire data sequence has been read:
public Object clone() throws CloneNotSupportedException
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