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.InputStream; import java.io.FilterInputStream; import java.io.PrintStream; import java.io.ByteArrayInputStream; /** * 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 input stream's * {@link #read() read} 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 read} 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. * * <p>Note that digest objects can compute only one digest (see * {@link MessageDigest}), * so that in order to compute intermediate digests, a caller should * retain a handle onto the digest object, and clone it for each * digest to be computed, leaving the original digest untouched. * * @see MessageDigest * * @see DigestOutputStream * * @author Benjamin Renaud * @since 1.2 */ public class DigestInputStream extends FilterInputStream { /* NOTE: This should be made a generic UpdaterInputStream */ /* Are we on or off? */ private boolean on = true; /** * The message digest associated with this stream. */ protected MessageDigest digest; /** * Creates a digest input stream, using the specified input stream * and message digest. * * @param stream the input stream. * * @param digest the message digest to associate with this stream. */ public DigestInputStream(InputStream 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; } /** * Reads a byte, and updates the message digest (if the digest * function is on). That is, this method reads a byte from the * input stream, blocking until the byte is actually read. If the * digest function is on (see {@link #on(boolean) on}), this method * will then call {@code update} on the message digest associated * with this stream, passing it the byte read. * * @return the byte read. * * @exception IOException if an I/O error occurs. * * @see MessageDigest#update(byte) */ public int read() throws IOException { int ch = in.read(); if (on && ch != -1) { digest.update((byte) ch); } return ch; } /** * Reads into a byte array, and updates the message digest (if the * digest function is on). That is, this method reads up to * {@code len} bytes from the input stream into the array * {@code b}, starting at offset {@code off}. This method * blocks until the data is actually * read. If the digest function is on (see * {@link #on(boolean) on}), this method will then call {@code update} * on the message digest associated with this stream, passing it * the data. * * @param b the array into which the data is read. * * @param off the starting offset into {@code b} of where the * data should be placed. * * @param len the maximum number of bytes to be read from the input * stream into b, starting at offset {@code off}. * * @return the actual number of bytes read. This is less than * {@code len} if the end of the stream is reached prior to * reading {@code len} bytes. -1 is returned if no bytes were * read because the end of the stream had already been reached when * the call was made. * * @exception IOException if an I/O error occurs. * * @see MessageDigest#update(byte[], int, int) */ public int read(byte[] b, int off, int len) throws IOException { int result = in.read(b, off, len); if (on && result != -1) { digest.update(b, off, result); } return result; } /** * Turns the digest function on or off. The default is on. When * it is on, a call to one of the {@code read} 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 input stream and * its associated message digest object. */ public String toString() { return "[Digest Input Stream] " + digest.toString(); } }