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1 /* |
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2 * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Oracle designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Oracle in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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22 * or visit www.oracle.com if you need additional information or have any |
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23 * questions. |
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24 */ |
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25 |
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26 package java.nio.channels; |
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27 |
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28 import java.nio.ByteBuffer; |
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29 import java.io.IOException; |
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30 |
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31 /** |
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32 * A byte channel that maintains a current <i>position</i> and allows the |
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33 * position to be changed. |
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34 * |
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35 * <p> A seekable byte channel is connected to an entity, typically a file, |
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36 * that contains a variable-length sequence of bytes that can be read and |
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37 * written. The current position can be {@link #position() <i>queried</i>} and |
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38 * {@link #position(long) <i>modified</i>}. The channel also provides access to |
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39 * the current <i>size</i> of the entity to which the channel is connected. The |
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40 * size increases when bytes are written beyond its current size; the size |
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41 * decreases when it is {@link #truncate <i>truncated</i>}. |
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42 * |
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43 * <p> The {@link #position(long) position} and {@link #truncate truncate} methods |
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44 * which do not otherwise have a value to return are specified to return the |
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45 * channel upon which they are invoked. This allows method invocations to be |
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46 * chained. Implementations of this interface should specialize the return type |
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47 * so that method invocations on the implementation class can be chained. |
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48 * |
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49 * @since 1.7 |
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50 * @see java.nio.file.Files#newByteChannel |
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51 */ |
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52 |
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53 public interface SeekableByteChannel |
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54 extends ByteChannel |
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55 { |
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56 /** |
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57 * Reads a sequence of bytes from this channel into the given buffer. |
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58 * |
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59 * <p> Bytes are read starting at this channel's current position, and |
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60 * then the position is updated with the number of bytes actually read. |
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61 * Otherwise this method behaves exactly as specified in the {@link |
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62 * ReadableByteChannel} interface. |
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63 */ |
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64 @Override |
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65 int read(ByteBuffer dst) throws IOException; |
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66 |
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67 /** |
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68 * Writes a sequence of bytes to this channel from the given buffer. |
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69 * |
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70 * <p> Bytes are written starting at this channel's current position, unless |
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71 * the channel is connected to an entity such as a file that is opened with |
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72 * the {@link java.nio.file.StandardOpenOption#APPEND APPEND} option, in |
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73 * which case the position is first advanced to the end. The entity to which |
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74 * the channel is connected is grown, if necessary, to accommodate the |
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75 * written bytes, and then the position is updated with the number of bytes |
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76 * actually written. Otherwise this method behaves exactly as specified by |
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77 * the {@link WritableByteChannel} interface. |
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78 */ |
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79 @Override |
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80 int write(ByteBuffer src) throws IOException; |
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81 |
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82 /** |
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83 * Returns this channel's position. |
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84 * |
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85 * @return This channel's position, |
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86 * a non-negative integer counting the number of bytes |
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87 * from the beginning of the entity to the current position |
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88 * |
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89 * @throws ClosedChannelException |
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90 * If this channel is closed |
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91 * @throws IOException |
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92 * If some other I/O error occurs |
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93 */ |
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94 long position() throws IOException; |
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95 |
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96 /** |
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97 * Sets this channel's position. |
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98 * |
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99 * <p> Setting the position to a value that is greater than the current size |
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100 * is legal but does not change the size of the entity. A later attempt to |
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101 * read bytes at such a position will immediately return an end-of-file |
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102 * indication. A later attempt to write bytes at such a position will cause |
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103 * the entity to grow to accommodate the new bytes; the values of any bytes |
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104 * between the previous end-of-file and the newly-written bytes are |
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105 * unspecified. |
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106 * |
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107 * <p> Setting the channel's position is not recommended when connected to |
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108 * an entity, typically a file, that is opened with the {@link |
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109 * java.nio.file.StandardOpenOption#APPEND APPEND} option. When opened for |
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110 * append, the position is first advanced to the end before writing. |
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111 * |
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112 * @param newPosition |
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113 * The new position, a non-negative integer counting |
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114 * the number of bytes from the beginning of the entity |
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115 * |
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116 * @return This channel |
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117 * |
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118 * @throws ClosedChannelException |
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119 * If this channel is closed |
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120 * @throws IllegalArgumentException |
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121 * If the new position is negative |
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122 * @throws IOException |
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123 * If some other I/O error occurs |
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124 */ |
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125 SeekableByteChannel position(long newPosition) throws IOException; |
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126 |
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127 /** |
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128 * Returns the current size of entity to which this channel is connected. |
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129 * |
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130 * @return The current size, measured in bytes |
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131 * |
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132 * @throws ClosedChannelException |
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133 * If this channel is closed |
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134 * @throws IOException |
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135 * If some other I/O error occurs |
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136 */ |
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137 long size() throws IOException; |
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138 |
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139 /** |
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140 * Truncates the entity, to which this channel is connected, to the given |
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141 * size. |
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142 * |
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143 * <p> If the given size is less than the current size then the entity is |
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144 * truncated, discarding any bytes beyond the new end. If the given size is |
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145 * greater than or equal to the current size then the entity is not modified. |
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146 * In either case, if the current position is greater than the given size |
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147 * then it is set to that size. |
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148 * |
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149 * <p> An implementation of this interface may prohibit truncation when |
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150 * connected to an entity, typically a file, opened with the {@link |
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151 * java.nio.file.StandardOpenOption#APPEND APPEND} option. |
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152 * |
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153 * @param size |
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154 * The new size, a non-negative byte count |
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155 * |
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156 * @return This channel |
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157 * |
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158 * @throws NonWritableChannelException |
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159 * If this channel was not opened for writing |
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160 * @throws ClosedChannelException |
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161 * If this channel is closed |
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162 * @throws IllegalArgumentException |
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163 * If the new size is negative |
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164 * @throws IOException |
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165 * If some other I/O error occurs |
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166 */ |
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167 SeekableByteChannel truncate(long size) throws IOException; |
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168 } |