001 /*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.io;
018
019 import com.google.common.annotations.Beta;
020 import com.google.common.base.Preconditions;
021 import com.google.common.primitives.Ints;
022 import com.google.common.primitives.Longs;
023
024 import java.io.DataInput;
025 import java.io.DataInputStream;
026 import java.io.EOFException;
027 import java.io.FilterInputStream;
028 import java.io.IOException;
029 import java.io.InputStream;
030
031 /**
032 * An implementation of {@link DataInput} that uses little-endian byte ordering
033 * for reading {@code short}, {@code int}, {@code float}, {@code double}, and
034 * {@code long} values.
035 * <p>
036 * <b>Note:</b> This class intentionally violates the specification of its
037 * supertype {@code DataInput}, which explicitly requires big-endian byte order.
038 *
039 * @author chrisn@google.com (Chris Nokleberg)
040 * @author kbottner@google.com (Keith Bottner)
041 * @since 8
042 */
043 @Beta
044 public final class LittleEndianDataInputStream extends FilterInputStream
045 implements DataInput {
046
047 /**
048 * Creates a {@code LittleEndianDataInputStream} that wraps the given stream.
049 *
050 * @param in the stream to delegate to
051 */
052 public LittleEndianDataInputStream(InputStream in) {
053 super(Preconditions.checkNotNull(in));
054 }
055
056 /**
057 * This method will throw a {@link UnsupportedOperationException}.
058 */
059 @Override
060 public String readLine() {
061 throw new UnsupportedOperationException("readLine is not supported");
062 }
063
064 @Override
065 public void readFully(byte[] b) throws IOException {
066 ByteStreams.readFully(this, b);
067 }
068
069 @Override
070 public void readFully(byte[] b, int off, int len) throws IOException {
071 ByteStreams.readFully(this, b, off, len);
072 }
073
074 @Override
075 public int skipBytes(int n) throws IOException {
076 return (int) in.skip(n);
077 }
078
079 @Override
080 public int readUnsignedByte() throws IOException {
081 int b1 = in.read();
082 if (0 > b1) {
083 throw new EOFException();
084 }
085
086 return b1;
087 }
088
089 /**
090 * Reads an unsigned {@code short} as specified by
091 * {@link DataInputStream#readUnsignedShort()}, except using little-endian
092 * byte order.
093 *
094 * @return the next two bytes of the input stream, interpreted as an {@code
095 * int} in little-endian byte order
096 * @throws IOException if an I/O error occurs
097 */
098 @Override
099 public int readUnsignedShort() throws IOException {
100 byte b1 = readAndCheckByte();
101 byte b2 = readAndCheckByte();
102
103 return Ints.fromBytes((byte) 0, (byte) 0, b2, b1);
104 }
105
106 /**
107 * Reads an integer as specified by {@link DataInputStream#readInt()}, except
108 * using little-endian byte order.
109 *
110 * @return the next four bytes of the input stream, interpreted as an {@code
111 * int} in little-endian byte order
112 * @throws IOException if an I/O error occurs
113 */
114 @Override
115 public int readInt() throws IOException {
116 byte b1 = readAndCheckByte();
117 byte b2 = readAndCheckByte();
118 byte b3 = readAndCheckByte();
119 byte b4 = readAndCheckByte();
120
121 return Ints.fromBytes( b4, b3, b2, b1);
122 }
123
124 /**
125 * Reads a {@code long} as specified by {@link DataInputStream#readLong()},
126 * except using little-endian byte order.
127 *
128 * @return the next eight bytes of the input stream, interpreted as a {@code
129 * long} in little-endian byte order
130 * @throws IOException if an I/O error occurs
131 */
132 @Override
133 public long readLong() throws IOException {
134 byte b1 = readAndCheckByte();
135 byte b2 = readAndCheckByte();
136 byte b3 = readAndCheckByte();
137 byte b4 = readAndCheckByte();
138 byte b5 = readAndCheckByte();
139 byte b6 = readAndCheckByte();
140 byte b7 = readAndCheckByte();
141 byte b8 = readAndCheckByte();
142
143 return Longs.fromBytes(b8, b7, b6, b5, b4, b3, b2, b1);
144 }
145
146 /**
147 * Reads a {@code float} as specified by {@link DataInputStream#readFloat()},
148 * except using little-endian byte order.
149 *
150 * @return the next four bytes of the input stream, interpreted as an {@code
151 * float} in little-endian byte order
152 * @throws IOException if an I/O error occurs
153 */
154 @Override
155 public float readFloat() throws IOException {
156 return Float.intBitsToFloat(readInt());
157 }
158
159 /**
160 * Reads a {@code double} as specified by
161 * {@link DataInputStream#readDouble()}, except using little-endian byte
162 * order.
163 *
164 * @return the next eight bytes of the input stream, interpreted as an {@code
165 * int} in little-endian byte order
166 * @throws IOException if an I/O error occurs
167 */
168 @Override
169 public double readDouble() throws IOException {
170 return Double.longBitsToDouble(readLong());
171 }
172
173 @Override
174 public String readUTF() throws IOException {
175 return new DataInputStream(in).readUTF();
176 }
177
178 /**
179 * Reads a {@code short} as specified by {@link DataInputStream#readShort()},
180 * except using little-endian byte order.
181 *
182 * @return the next two bytes of the input stream, interpreted as an {@code
183 * short} in little-endian byte order.
184 * @throws IOException if an I/O error occurs.
185 */
186 @Override
187 public short readShort() throws IOException {
188 return (short) readUnsignedShort();
189 }
190
191 /**
192 * Reads a char as specified by {@link DataInputStream#readChar()}, except
193 * using little-endian byte order.
194 *
195 * @return the next two bytes of the input stream, interpreted as an {@code
196 * char} in little-endian byte order
197 * @throws IOException if an I/O error occurs
198 */
199 @Override
200 public char readChar() throws IOException {
201 return (char) readUnsignedShort();
202 }
203
204 @Override
205 public byte readByte() throws IOException {
206 return (byte) readUnsignedByte();
207 }
208
209 @Override
210 public boolean readBoolean() throws IOException {
211 return readUnsignedByte() != 0;
212 }
213
214 /**
215 * Reads a byte from the input stream checking that the end of file (EOF)
216 * has not been encountered.
217 *
218 * @return byte read from input
219 * @throws IOException if an error is encountered while reading
220 * @throws EOFException if the end of file (EOF) is encountered.
221 */
222 private byte readAndCheckByte() throws IOException, EOFException {
223 int b1 = in.read();
224
225 if (-1 == b1) {
226 throw new EOFException();
227 }
228
229 return (byte) b1;
230 }
231
232 }