1 /*
2 * Copyright (c) 1994, 2018, 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 11
65 */
66 public static OutputStream nullOutputStream() {
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 public void write(byte b[], int off, int len) throws IOException {
83 Objects.checkFromIndexSize(off, len, b.length);
84 ensureOpen();
85 }
86
87 @Override
88 public void close() {
89 closed = true;
90 }
91 };
92 }
93
94 /**
95 * Writes the specified byte to this output stream. The general
96 * contract for <code>write</code> is that one byte is written
97 * to the output stream. The byte to be written is the eight
98 * low-order bits of the argument <code>b</code>. The 24
99 * high-order bits of <code>b</code> are ignored.
100 * <p>
101 * Subclasses of <code>OutputStream</code> must provide an
102 * implementation for this method.
103 *
104 * @param b the <code>byte</code>.
105 * @exception IOException if an I/O error occurs. In particular,
106 * an <code>IOException</code> may be thrown if the
107 * output stream has been closed.
108 */
109 public abstract void write(int b) throws IOException;
110
111 /**
112 * Writes <code>b.length</code> bytes from the specified byte array
113 * to this output stream. The general contract for <code>write(b)</code>
114 * is that it should have exactly the same effect as the call
115 * <code>write(b, 0, b.length)</code>.
116 *
117 * @param b the data.
118 * @exception IOException if an I/O error occurs.
119 * @see java.io.OutputStream#write(byte[], int, int)
120 */
121 public void write(byte b[]) throws IOException {
122 write(b, 0, b.length);
123 }
124
125 /**
126 * Writes <code>len</code> bytes from the specified byte array
127 * starting at offset <code>off</code> to this output stream.
128 * The general contract for <code>write(b, off, len)</code> is that
129 * some of the bytes in the array <code>b</code> are written to the
130 * output stream in order; element <code>b[off]</code> is the first
131 * byte written and <code>b[off+len-1]</code> is the last byte written
132 * by this operation.
133 * <p>
134 * The <code>write</code> method of <code>OutputStream</code> calls
135 * the write method of one argument on each of the bytes to be
136 * written out. Subclasses are encouraged to override this method and
137 * provide a more efficient implementation.
138 * <p>
139 * If <code>b</code> is <code>null</code>, a
140 * <code>NullPointerException</code> is thrown.
141 * <p>
142 * If <code>off</code> is negative, or <code>len</code> is negative, or
143 * <code>off+len</code> is greater than the length of the array
144 * {@code b}, then an {@code IndexOutOfBoundsException} is thrown.
145 *
146 * @param b the data.
147 * @param off the start offset in the data.
148 * @param len the number of bytes to write.
149 * @exception IOException if an I/O error occurs. In particular,
150 * an <code>IOException</code> is thrown if the output
151 * stream is closed.
152 */
153 public void write(byte b[], int off, int len) throws IOException {
154 Objects.checkFromIndexSize(off, len, b.length);
155 // len == 0 condition implicitly handled by loop bounds
156 for (int i = 0 ; i < len ; i++) {
157 write(b[off + i]);
158 }
159 }
160
161 /**
162 * Flushes this output stream and forces any buffered output bytes
163 * to be written out. The general contract of <code>flush</code> is
164 * that calling it is an indication that, if any bytes previously
165 * written have been buffered by the implementation of the output
166 * stream, such bytes should immediately be written to their
167 * intended destination.
168 * <p>
169 * If the intended destination of this stream is an abstraction provided by
170 * the underlying operating system, for example a file, then flushing the
171 * stream guarantees only that bytes previously written to the stream are
172 * passed to the operating system for writing; it does not guarantee that
173 * they are actually written to a physical device such as a disk drive.
174 * <p>
175 * The <code>flush</code> method of <code>OutputStream</code> does nothing.
176 *
177 * @exception IOException if an I/O error occurs.
178 */
179 public void flush() throws IOException {
180 }
181
182 /**
183 * Closes this output stream and releases any system resources
184 * associated with this stream. The general contract of <code>close</code>
185 * is that it closes the output stream. A closed stream cannot perform
186 * output operations and cannot be reopened.
187 * <p>
188 * The <code>close</code> method of <code>OutputStream</code> does nothing.
189 *
190 * @exception IOException if an I/O error occurs.
191 */
192 public void close() throws IOException {
193 }
194
195 }