Java tutorial
/* * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.security; import java.io.IOException; import java.io.EOFException; import java.io.OutputStream; import java.io.FilterOutputStream; import java.io.PrintStream; import java.io.ByteArrayOutputStream; /** * A transparent stream that updates the associated message digest using * the bits going through the stream. * * <p>To complete the message digest computation, call one of the * {@code digest} methods on the associated message * digest after your calls to one of this digest output stream's * {@link #write(int) write} methods. * * <p>It is possible to turn this stream on or off (see * {@link #on(boolean) on}). When it is on, a call to one of the * {@code write} methods results in * an update on the message digest. But when it is off, the message * digest is not updated. The default is for the stream to be on. * * @see MessageDigest * @see DigestInputStream * * @author Benjamin Renaud * @since 1.2 */ public class DigestOutputStream extends FilterOutputStream { private boolean on = true; /** * The message digest associated with this stream. */ protected MessageDigest digest; /** * Creates a digest output stream, using the specified output stream * and message digest. * * @param stream the output stream. * * @param digest the message digest to associate with this stream. */ public DigestOutputStream(OutputStream stream, MessageDigest digest) { super(stream); setMessageDigest(digest); } /** * Returns the message digest associated with this stream. * * @return the message digest associated with this stream. * @see #setMessageDigest(java.security.MessageDigest) */ public MessageDigest getMessageDigest() { return digest; } /** * Associates the specified message digest with this stream. * * @param digest the message digest to be associated with this stream. * @see #getMessageDigest() */ public void setMessageDigest(MessageDigest digest) { this.digest = digest; } /** * Updates the message digest (if the digest function is on) using * the specified byte, and in any case writes the byte * to the output stream. That is, if the digest function is on * (see {@link #on(boolean) on}), this method calls * {@code update} on the message digest associated with this * stream, passing it the byte {@code b}. This method then * writes the byte to the output stream, blocking until the byte * is actually written. * * @param b the byte to be used for updating and writing to the * output stream. * * @exception IOException if an I/O error occurs. * * @see MessageDigest#update(byte) */ public void write(int b) throws IOException { out.write(b); if (on) { digest.update((byte) b); } } /** * Updates the message digest (if the digest function is on) using * the specified subarray, and in any case writes the subarray to * the output stream. That is, if the digest function is on (see * {@link #on(boolean) on}), this method calls {@code update} * on the message digest associated with this stream, passing it * the subarray specifications. This method then writes the subarray * bytes to the output stream, blocking until the bytes are actually * written. * * @param b the array containing the subarray to be used for updating * and writing to the output stream. * * @param off the offset into {@code b} of the first byte to * be updated and written. * * @param len the number of bytes of data to be updated and written * from {@code b}, starting at offset {@code off}. * * @exception IOException if an I/O error occurs. * * @see MessageDigest#update(byte[], int, int) */ public void write(byte[] b, int off, int len) throws IOException { out.write(b, off, len); if (on) { digest.update(b, off, len); } } /** * Turns the digest function on or off. The default is on. When * it is on, a call to one of the {@code write} methods results in an * update on the message digest. But when it is off, the message * digest is not updated. * * @param on true to turn the digest function on, false to turn it * off. */ public void on(boolean on) { this.on = on; } /** * Prints a string representation of this digest output stream and * its associated message digest object. */ public String toString() { return "[Digest Output Stream] " + digest.toString(); } }