1 /* 2 * Copyright (c) 1994, 2017, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.io; 27 28 import java.util.Objects; 29 30 /** 31 * This abstract class is the superclass of all classes representing 32 * an output stream of bytes. An output stream accepts output bytes 33 * and sends them to some sink. 34 * <p> 35 * Applications that need to define a subclass of 36 * <code>OutputStream</code> must always provide at least a method 37 * that writes one byte of output. 38 * 39 * @author Arthur van Hoff 40 * @see java.io.BufferedOutputStream 41 * @see java.io.ByteArrayOutputStream 42 * @see java.io.DataOutputStream 43 * @see java.io.FilterOutputStream 44 * @see java.io.InputStream 45 * @see java.io.OutputStream#write(int) 46 * @since 1.0 47 */ 48 public abstract class OutputStream implements Closeable, Flushable { 49 /** 50 * Returns a new {@code OutputStream} which discards all bytes. The 51 * returned stream is initially open. The stream is closed by calling 52 * the {@code close()} method. Subsequent calls to {@code close()} have 53 * no effect. 54 * 55 * <p> While the stream is open, the {@code write(int)}, {@code 56 * write(byte[])}, and {@code write(byte[], int, int)} methods do nothing. 57 * After the stream has been closed, these methods all throw {@code 58 * IOException}. 59 * 60 * <p> The {@code flush()} method does nothing. 61 * 62 * @return an {@code OutputStream} which discards all bytes 63 * 64 * @since 10 65 */ 66 public static OutputStream nullStream() { 67 return new OutputStream() { 68 private volatile boolean closed; 69 70 private void ensureOpen() throws IOException { 71 if (closed) { 72 throw new IOException("Stream closed"); 73 } 74 } 75 76 @Override 77 public void write(int b) throws IOException { 78 ensureOpen(); 79 } 80 81 @Override 82 // overridden for efficiency 83 public void write(byte b[], int off, int len) throws IOException { 84 if (b == null) { 85 throw new NullPointerException(); 86 } else if (off < 0 || len < 0 || len > b.length - off) { 87 throw new IndexOutOfBoundsException(); 88 } 89 ensureOpen(); 90 } 91 92 @Override 93 public void close() { 94 closed = true; 95 } 96 }; 97 } 98 99 /** 100 * Writes the specified byte to this output stream. The general 101 * contract for <code>write</code> is that one byte is written 102 * to the output stream. The byte to be written is the eight 103 * low-order bits of the argument <code>b</code>. The 24 104 * high-order bits of <code>b</code> are ignored. 105 * <p> 106 * Subclasses of <code>OutputStream</code> must provide an 107 * implementation for this method. 108 * 109 * @param b the <code>byte</code>. 110 * @exception IOException if an I/O error occurs. In particular, 111 * an <code>IOException</code> may be thrown if the 112 * output stream has been closed. 113 */ 114 public abstract void write(int b) throws IOException; 115 116 /** 117 * Writes <code>b.length</code> bytes from the specified byte array 118 * to this output stream. The general contract for <code>write(b)</code> 119 * is that it should have exactly the same effect as the call 120 * <code>write(b, 0, b.length)</code>. 121 * 122 * @param b the data. 123 * @exception IOException if an I/O error occurs. 124 * @see java.io.OutputStream#write(byte[], int, int) 125 */ 126 public void write(byte b[]) throws IOException { 127 write(b, 0, b.length); 128 } 129 130 /** 131 * Writes <code>len</code> bytes from the specified byte array 132 * starting at offset <code>off</code> to this output stream. 133 * The general contract for <code>write(b, off, len)</code> is that 134 * some of the bytes in the array <code>b</code> are written to the 135 * output stream in order; element <code>b[off]</code> is the first 136 * byte written and <code>b[off+len-1]</code> is the last byte written 137 * by this operation. 138 * <p> 139 * The <code>write</code> method of <code>OutputStream</code> calls 140 * the write method of one argument on each of the bytes to be 141 * written out. Subclasses are encouraged to override this method and 142 * provide a more efficient implementation. 143 * <p> 144 * If <code>b</code> is <code>null</code>, a 145 * <code>NullPointerException</code> is thrown. 146 * <p> 147 * If <code>off</code> is negative, or <code>len</code> is negative, or 148 * <code>off+len</code> is greater than the length of the array 149 * {@code b}, then an {@code IndexOutOfBoundsException} is thrown. 150 * 151 * @param b the data. 152 * @param off the start offset in the data. 153 * @param len the number of bytes to write. 154 * @exception IOException if an I/O error occurs. In particular, 155 * an <code>IOException</code> is thrown if the output 156 * stream is closed. 157 */ 158 public void write(byte b[], int off, int len) throws IOException { 159 Objects.requireNonNull(b); 160 Objects.checkFromIndexSize(off, len, b.length); 161 // len == 0 condition implicitly handled by loop bounds 162 for (int i = 0 ; i < len ; i++) { 163 write(b[off + i]); 164 } 165 } 166 167 /** 168 * Flushes this output stream and forces any buffered output bytes 169 * to be written out. The general contract of <code>flush</code> is 170 * that calling it is an indication that, if any bytes previously 171 * written have been buffered by the implementation of the output 172 * stream, such bytes should immediately be written to their 173 * intended destination. 174 * <p> 175 * If the intended destination of this stream is an abstraction provided by 176 * the underlying operating system, for example a file, then flushing the 177 * stream guarantees only that bytes previously written to the stream are 178 * passed to the operating system for writing; it does not guarantee that 179 * they are actually written to a physical device such as a disk drive. 180 * <p> 181 * The <code>flush</code> method of <code>OutputStream</code> does nothing. 182 * 183 * @exception IOException if an I/O error occurs. 184 */ 185 public void flush() throws IOException { 186 } 187 188 /** 189 * Closes this output stream and releases any system resources 190 * associated with this stream. The general contract of <code>close</code> 191 * is that it closes the output stream. A closed stream cannot perform 192 * output operations and cannot be reopened. 193 * <p> 194 * The <code>close</code> method of <code>OutputStream</code> does nothing. 195 * 196 * @exception IOException if an I/O error occurs. 197 */ 198 public void close() throws IOException { 199 } 200 201 }