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 Objects.requireNonNull(b);
85 Objects.checkFromIndexSize(off, len, b.length);
86 ensureOpen();
87 }
88
89 @Override
90 public void close() {
91 closed = true;
92 }
93 };
94 }
95
96 /**
97 * Writes the specified byte to this output stream. The general
98 * contract for <code>write</code> is that one byte is written
99 * to the output stream. The byte to be written is the eight
100 * low-order bits of the argument <code>b</code>. The 24
101 * high-order bits of <code>b</code> are ignored.
102 * <p>
103 * Subclasses of <code>OutputStream</code> must provide an
104 * implementation for this method.
105 *
106 * @param b the <code>byte</code>.
107 * @exception IOException if an I/O error occurs. In particular,
108 * an <code>IOException</code> may be thrown if the
109 * output stream has been closed.
110 */
111 public abstract void write(int b) throws IOException;
112
113 /**
114 * Writes <code>b.length</code> bytes from the specified byte array
115 * to this output stream. The general contract for <code>write(b)</code>
116 * is that it should have exactly the same effect as the call
117 * <code>write(b, 0, b.length)</code>.
118 *
119 * @param b the data.
120 * @exception IOException if an I/O error occurs.
121 * @see java.io.OutputStream#write(byte[], int, int)
122 */
123 public void write(byte b[]) throws IOException {
124 write(b, 0, b.length);
125 }
126
127 /**
128 * Writes <code>len</code> bytes from the specified byte array
129 * starting at offset <code>off</code> to this output stream.
130 * The general contract for <code>write(b, off, len)</code> is that
131 * some of the bytes in the array <code>b</code> are written to the
132 * output stream in order; element <code>b[off]</code> is the first
133 * byte written and <code>b[off+len-1]</code> is the last byte written
134 * by this operation.
135 * <p>
136 * The <code>write</code> method of <code>OutputStream</code> calls
137 * the write method of one argument on each of the bytes to be
138 * written out. Subclasses are encouraged to override this method and
139 * provide a more efficient implementation.
140 * <p>
141 * If <code>b</code> is <code>null</code>, a
142 * <code>NullPointerException</code> is thrown.
143 * <p>
144 * If <code>off</code> is negative, or <code>len</code> is negative, or
145 * <code>off+len</code> is greater than the length of the array
146 * {@code b}, then an {@code IndexOutOfBoundsException} is thrown.
147 *
148 * @param b the data.
149 * @param off the start offset in the data.
150 * @param len the number of bytes to write.
151 * @exception IOException if an I/O error occurs. In particular,
152 * an <code>IOException</code> is thrown if the output
153 * stream is closed.
154 */
155 public void write(byte b[], int off, int len) throws IOException {
156 Objects.requireNonNull(b);
157 Objects.checkFromIndexSize(off, len, b.length);
158 // len == 0 condition implicitly handled by loop bounds
159 for (int i = 0 ; i < len ; i++) {
160 write(b[off + i]);
161 }
162 }
163
164 /**
165 * Flushes this output stream and forces any buffered output bytes
166 * to be written out. The general contract of <code>flush</code> is
167 * that calling it is an indication that, if any bytes previously
168 * written have been buffered by the implementation of the output
169 * stream, such bytes should immediately be written to their
170 * intended destination.
171 * <p>
172 * If the intended destination of this stream is an abstraction provided by
173 * the underlying operating system, for example a file, then flushing the
174 * stream guarantees only that bytes previously written to the stream are
175 * passed to the operating system for writing; it does not guarantee that
176 * they are actually written to a physical device such as a disk drive.
177 * <p>
178 * The <code>flush</code> method of <code>OutputStream</code> does nothing.
179 *
180 * @exception IOException if an I/O error occurs.
181 */
182 public void flush() throws IOException {
183 }
184
185 /**
186 * Closes this output stream and releases any system resources
187 * associated with this stream. The general contract of <code>close</code>
188 * is that it closes the output stream. A closed stream cannot perform
189 * output operations and cannot be reopened.
190 * <p>
191 * The <code>close</code> method of <code>OutputStream</code> does nothing.
192 *
193 * @exception IOException if an I/O error occurs.
194 */
195 public void close() throws IOException {
196 }
197
198 }