Java tutorial
/* * Copyright (c) 1994, 2018, 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.io; import java.util.Arrays; import java.util.Objects; /** * A {@code ByteArrayInputStream} contains * an internal buffer that contains bytes that * may be read from the stream. An internal * counter keeps track of the next byte to * be supplied by the {@code read} method. * <p> * Closing a {@code ByteArrayInputStream} has no effect. The methods in * this class can be called after the stream has been closed without * generating an {@code IOException}. * * @author Arthur van Hoff * @see java.io.StringBufferInputStream * @since 1.0 */ public class ByteArrayInputStream extends InputStream { /** * An array of bytes that was provided * by the creator of the stream. Elements {@code buf[0]} * through {@code buf[count-1]} are the * only bytes that can ever be read from the * stream; element {@code buf[pos]} is * the next byte to be read. */ protected byte buf[]; /** * The index of the next character to read from the input stream buffer. * This value should always be nonnegative * and not larger than the value of {@code count}. * The next byte to be read from the input stream buffer * will be {@code buf[pos]}. */ protected int pos; /** * The currently marked position in the stream. * ByteArrayInputStream objects are marked at position zero by * default when constructed. They may be marked at another * position within the buffer by the {@code mark()} method. * The current buffer position is set to this point by the * {@code reset()} method. * <p> * If no mark has been set, then the value of mark is the offset * passed to the constructor (or 0 if the offset was not supplied). * * @since 1.1 */ protected int mark = 0; /** * The index one greater than the last valid character in the input * stream buffer. * This value should always be nonnegative * and not larger than the length of {@code buf}. * It is one greater than the position of * the last byte within {@code buf} that * can ever be read from the input stream buffer. */ protected int count; /** * Creates a {@code ByteArrayInputStream} * so that it uses {@code buf} as its * buffer array. * The buffer array is not copied. * The initial value of {@code pos} * is {@code 0} and the initial value * of {@code count} is the length of * {@code buf}. * * @param buf the input buffer. */ public ByteArrayInputStream(byte buf[]) { this.buf = buf; this.pos = 0; this.count = buf.length; } /** * Creates {@code ByteArrayInputStream} * that uses {@code buf} as its * buffer array. The initial value of {@code pos} * is {@code offset} and the initial value * of {@code count} is the minimum of {@code offset+length} * and {@code buf.length}. * The buffer array is not copied. The buffer's mark is * set to the specified offset. * * @param buf the input buffer. * @param offset the offset in the buffer of the first byte to read. * @param length the maximum number of bytes to read from the buffer. */ public ByteArrayInputStream(byte buf[], int offset, int length) { this.buf = buf; this.pos = offset; this.count = Math.min(offset + length, buf.length); this.mark = offset; } /** * Reads the next byte of data from this input stream. The value * byte is returned as an {@code int} in the range * {@code 0} to {@code 255}. If no byte is available * because the end of the stream has been reached, the value * {@code -1} is returned. * <p> * This {@code read} method * cannot block. * * @return the next byte of data, or {@code -1} if the end of the * stream has been reached. */ public synchronized int read() { return (pos < count) ? (buf[pos++] & 0xff) : -1; } /** * Reads up to {@code len} bytes of data into an array of bytes from this * input stream. If {@code pos} equals {@code count}, then {@code -1} is * returned to indicate end of file. Otherwise, the number {@code k} of * bytes read is equal to the smaller of {@code len} and {@code count-pos}. * If {@code k} is positive, then bytes {@code buf[pos]} through * {@code buf[pos+k-1]} are copied into {@code b[off]} through * {@code b[off+k-1]} in the manner performed by {@code System.arraycopy}. * The value {@code k} is added into {@code pos} and {@code k} is returned. * <p> * This {@code read} method cannot block. * * @param b the buffer into which the data is read. * @param off the start offset in the destination array {@code b} * @param len the maximum number of bytes read. * @return the total number of bytes read into the buffer, or * {@code -1} if there is no more data because the end of * the stream has been reached. * @throws NullPointerException If {@code b} is {@code null}. * @throws IndexOutOfBoundsException If {@code off} is negative, * {@code len} is negative, or {@code len} is greater than * {@code b.length - off} */ public synchronized int read(byte b[], int off, int len) { Objects.checkFromIndexSize(off, len, b.length); if (pos >= count) { return -1; } int avail = count - pos; if (len > avail) { len = avail; } if (len <= 0) { return 0; } System.arraycopy(buf, pos, b, off, len); pos += len; return len; } public synchronized byte[] readAllBytes() { byte[] result = Arrays.copyOfRange(buf, pos, count); pos = count; return result; } public int readNBytes(byte[] b, int off, int len) { int n = read(b, off, len); return n == -1 ? 0 : n; } public synchronized long transferTo(OutputStream out) throws IOException { int len = count - pos; out.write(buf, pos, len); pos = count; return len; } /** * Skips {@code n} bytes of input from this input stream. Fewer * bytes might be skipped if the end of the input stream is reached. * The actual number {@code k} * of bytes to be skipped is equal to the smaller * of {@code n} and {@code count-pos}. * The value {@code k} is added into {@code pos} * and {@code k} is returned. * * @param n the number of bytes to be skipped. * @return the actual number of bytes skipped. */ public synchronized long skip(long n) { long k = count - pos; if (n < k) { k = n < 0 ? 0 : n; } pos += k; return k; } /** * Returns the number of remaining bytes that can be read (or skipped over) * from this input stream. * <p> * The value returned is {@code count - pos}, * which is the number of bytes remaining to be read from the input buffer. * * @return the number of remaining bytes that can be read (or skipped * over) from this input stream without blocking. */ public synchronized int available() { return count - pos; } /** * Tests if this {@code InputStream} supports mark/reset. The * {@code markSupported} method of {@code ByteArrayInputStream} * always returns {@code true}. * * @since 1.1 */ public boolean markSupported() { return true; } /** * Set the current marked position in the stream. * ByteArrayInputStream objects are marked at position zero by * default when constructed. They may be marked at another * position within the buffer by this method. * <p> * If no mark has been set, then the value of the mark is the * offset passed to the constructor (or 0 if the offset was not * supplied). * * <p> Note: The {@code readAheadLimit} for this class * has no meaning. * * @since 1.1 */ public void mark(int readAheadLimit) { mark = pos; } /** * Resets the buffer to the marked position. The marked position * is 0 unless another position was marked or an offset was specified * in the constructor. */ public synchronized void reset() { pos = mark; } /** * Closing a {@code ByteArrayInputStream} has no effect. The methods in * this class can be called after the stream has been closed without * generating an {@code IOException}. */ public void close() throws IOException { } }