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1 /* |
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2 * Copyright 2000-2005 Sun Microsystems, Inc. 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. Sun designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
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22 * CA 95054 USA or visit www.sun.com if you need additional information or |
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23 * have any 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.io.*; |
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29 import java.nio.ByteBuffer; |
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30 import java.nio.MappedByteBuffer; |
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31 import java.nio.channels.spi.AbstractInterruptibleChannel; |
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32 |
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33 |
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34 /** |
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35 * A channel for reading, writing, mapping, and manipulating a file. |
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36 * |
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37 * <p> A file channel has a current <i>position</i> within its file which can |
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38 * be both {@link #position() </code>queried<code>} and {@link #position(long) |
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39 * </code>modified<code>}. The file itself contains a variable-length sequence |
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40 * of bytes that can be read and written and whose current {@link #size |
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41 * </code><i>size</i><code>} can be queried. The size of the file increases |
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42 * when bytes are written beyond its current size; the size of the file |
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43 * decreases when it is {@link #truncate </code><i>truncated</i><code>}. The |
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44 * file may also have some associated <i>metadata</i> such as access |
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45 * permissions, content type, and last-modification time; this class does not |
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46 * define methods for metadata access. |
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47 * |
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48 * <p> In addition to the familiar read, write, and close operations of byte |
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49 * channels, this class defines the following file-specific operations: </p> |
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50 * |
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51 * <ul> |
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52 * |
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53 * <li><p> Bytes may be {@link #read(ByteBuffer, long) </code>read<code>} or |
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54 * {@link #write(ByteBuffer, long) </code>written<code>} at an absolute |
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55 * position in a file in a way that does not affect the channel's current |
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56 * position. </p></li> |
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57 * |
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58 * <li><p> A region of a file may be {@link #map </code>mapped<code>} |
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59 * directly into memory; for large files this is often much more efficient |
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60 * than invoking the usual <tt>read</tt> or <tt>write</tt> methods. |
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61 * </p></li> |
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62 * |
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63 * <li><p> Updates made to a file may be {@link #force </code>forced |
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64 * out<code>} to the underlying storage device, ensuring that data are not |
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65 * lost in the event of a system crash. </p></li> |
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66 * |
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67 * <li><p> Bytes can be transferred from a file {@link #transferTo </code>to |
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68 * some other channel<code>}, and {@link #transferFrom </code>vice |
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69 * versa<code>}, in a way that can be optimized by many operating systems |
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70 * into a very fast transfer directly to or from the filesystem cache. |
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71 * </p></li> |
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72 * |
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73 * <li><p> A region of a file may be {@link FileLock </code>locked<code>} |
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74 * against access by other programs. </p></li> |
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75 * |
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76 * </ul> |
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77 * |
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78 * <p> File channels are safe for use by multiple concurrent threads. The |
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79 * {@link Channel#close close} method may be invoked at any time, as specified |
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80 * by the {@link Channel} interface. Only one operation that involves the |
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81 * channel's position or can change its file's size may be in progress at any |
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82 * given time; attempts to initiate a second such operation while the first is |
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83 * still in progress will block until the first operation completes. Other |
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84 * operations, in particular those that take an explicit position, may proceed |
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85 * concurrently; whether they in fact do so is dependent upon the underlying |
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86 * implementation and is therefore unspecified. |
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87 * |
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88 * <p> The view of a file provided by an instance of this class is guaranteed |
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89 * to be consistent with other views of the same file provided by other |
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90 * instances in the same program. The view provided by an instance of this |
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91 * class may or may not, however, be consistent with the views seen by other |
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92 * concurrently-running programs due to caching performed by the underlying |
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93 * operating system and delays induced by network-filesystem protocols. This |
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94 * is true regardless of the language in which these other programs are |
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95 * written, and whether they are running on the same machine or on some other |
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96 * machine. The exact nature of any such inconsistencies are system-dependent |
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97 * and are therefore unspecified. |
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98 * |
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99 * <p> This class does not define methods for opening existing files or for |
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100 * creating new ones; such methods may be added in a future release. In this |
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101 * release a file channel can be obtained from an existing {@link |
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102 * java.io.FileInputStream#getChannel FileInputStream}, {@link |
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103 * java.io.FileOutputStream#getChannel FileOutputStream}, or {@link |
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104 * java.io.RandomAccessFile#getChannel RandomAccessFile} object by invoking |
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105 * that object's <tt>getChannel</tt> method, which returns a file channel that |
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106 * is connected to the same underlying file. |
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107 * |
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108 * <p> The state of a file channel is intimately connected to that of the |
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109 * object whose <tt>getChannel</tt> method returned the channel. Changing the |
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110 * channel's position, whether explicitly or by reading or writing bytes, will |
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111 * change the file position of the originating object, and vice versa. |
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112 * Changing the file's length via the file channel will change the length seen |
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113 * via the originating object, and vice versa. Changing the file's content by |
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114 * writing bytes will change the content seen by the originating object, and |
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115 * vice versa. |
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116 * |
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117 * <a name="open-mode"><p> At various points this class specifies that an |
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118 * instance that is "open for reading," "open for writing," or "open for |
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119 * reading and writing" is required. A channel obtained via the {@link |
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120 * java.io.FileInputStream#getChannel getChannel} method of a {@link |
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121 * java.io.FileInputStream} instance will be open for reading. A channel |
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122 * obtained via the {@link java.io.FileOutputStream#getChannel getChannel} |
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123 * method of a {@link java.io.FileOutputStream} instance will be open for |
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124 * writing. Finally, a channel obtained via the {@link |
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125 * java.io.RandomAccessFile#getChannel getChannel} method of a {@link |
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126 * java.io.RandomAccessFile} instance will be open for reading if the instance |
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127 * was created with mode <tt>"r"</tt> and will be open for reading and writing |
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128 * if the instance was created with mode <tt>"rw"</tt>. |
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129 * |
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130 * <a name="append-mode"><p> A file channel that is open for writing may be in |
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131 * <i>append mode</i>, for example if it was obtained from a file-output stream |
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132 * that was created by invoking the {@link |
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133 * java.io.FileOutputStream#FileOutputStream(java.io.File,boolean) |
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134 * FileOutputStream(File,boolean)} constructor and passing <tt>true</tt> for |
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135 * the second parameter. In this mode each invocation of a relative write |
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136 * operation first advances the position to the end of the file and then writes |
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137 * the requested data. Whether the advancement of the position and the writing |
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138 * of the data are done in a single atomic operation is system-dependent and |
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139 * therefore unspecified. |
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140 * |
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141 * |
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142 * @see java.io.FileInputStream#getChannel() |
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143 * @see java.io.FileOutputStream#getChannel() |
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144 * @see java.io.RandomAccessFile#getChannel() |
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145 * |
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146 * @author Mark Reinhold |
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147 * @author Mike McCloskey |
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148 * @author JSR-51 Expert Group |
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149 * @since 1.4 |
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150 */ |
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151 |
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152 public abstract class FileChannel |
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153 extends AbstractInterruptibleChannel |
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154 implements ByteChannel, GatheringByteChannel, ScatteringByteChannel |
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155 { |
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156 |
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157 /** |
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158 * Initializes a new instance of this class. |
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159 */ |
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160 protected FileChannel() { } |
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161 |
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162 |
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163 // -- Channel operations -- |
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164 |
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165 /** |
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166 * Reads a sequence of bytes from this channel into the given buffer. |
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167 * |
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168 * <p> Bytes are read starting at this channel's current file position, and |
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169 * then the file position is updated with the number of bytes actually |
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170 * read. Otherwise this method behaves exactly as specified in the {@link |
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171 * ReadableByteChannel} interface. </p> |
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172 */ |
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173 public abstract int read(ByteBuffer dst) throws IOException; |
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174 |
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175 /** |
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176 * Reads a sequence of bytes from this channel into a subsequence of the |
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177 * given buffers. |
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178 * |
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179 * <p> Bytes are read starting at this channel's current file position, and |
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180 * then the file position is updated with the number of bytes actually |
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181 * read. Otherwise this method behaves exactly as specified in the {@link |
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182 * ScatteringByteChannel} interface. </p> |
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183 */ |
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184 public abstract long read(ByteBuffer[] dsts, int offset, int length) |
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185 throws IOException; |
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186 |
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187 /** |
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188 * Reads a sequence of bytes from this channel into the given buffers. |
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189 * |
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190 * <p> Bytes are read starting at this channel's current file position, and |
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191 * then the file position is updated with the number of bytes actually |
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192 * read. Otherwise this method behaves exactly as specified in the {@link |
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193 * ScatteringByteChannel} interface. </p> |
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194 */ |
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195 public final long read(ByteBuffer[] dsts) throws IOException { |
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196 return read(dsts, 0, dsts.length); |
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197 } |
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198 |
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199 /** |
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200 * Writes a sequence of bytes to this channel from the given buffer. |
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201 * |
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202 * <p> Bytes are written starting at this channel's current file position |
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203 * unless the channel is in append mode, in which case the position is |
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204 * first advanced to the end of the file. The file is grown, if necessary, |
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205 * to accommodate the written bytes, and then the file position is updated |
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206 * with the number of bytes actually written. Otherwise this method |
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207 * behaves exactly as specified by the {@link WritableByteChannel} |
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208 * interface. </p> |
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209 */ |
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210 public abstract int write(ByteBuffer src) throws IOException; |
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211 |
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212 /** |
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213 * Writes a sequence of bytes to this channel from a subsequence of the |
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214 * given buffers. |
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215 * |
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216 * <p> Bytes are written starting at this channel's current file position |
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217 * unless the channel is in append mode, in which case the position is |
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218 * first advanced to the end of the file. The file is grown, if necessary, |
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219 * to accommodate the written bytes, and then the file position is updated |
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220 * with the number of bytes actually written. Otherwise this method |
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221 * behaves exactly as specified in the {@link GatheringByteChannel} |
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222 * interface. </p> |
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223 */ |
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224 public abstract long write(ByteBuffer[] srcs, int offset, int length) |
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225 throws IOException; |
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226 |
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227 /** |
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228 * Writes a sequence of bytes to this channel from the given buffers. |
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229 * |
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230 * <p> Bytes are written starting at this channel's current file position |
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231 * unless the channel is in append mode, in which case the position is |
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232 * first advanced to the end of the file. The file is grown, if necessary, |
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233 * to accommodate the written bytes, and then the file position is updated |
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234 * with the number of bytes actually written. Otherwise this method |
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235 * behaves exactly as specified in the {@link GatheringByteChannel} |
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236 * interface. </p> |
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237 */ |
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238 public final long write(ByteBuffer[] srcs) throws IOException { |
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239 return write(srcs, 0, srcs.length); |
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240 } |
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241 |
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242 |
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243 // -- Other operations -- |
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244 |
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245 /** |
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246 * Returns this channel's file position. </p> |
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247 * |
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248 * @return This channel's file position, |
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249 * a non-negative integer counting the number of bytes |
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250 * from the beginning of the file to the current position |
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251 * |
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252 * @throws ClosedChannelException |
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253 * If this channel is closed |
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254 * |
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255 * @throws IOException |
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256 * If some other I/O error occurs |
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257 */ |
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258 public abstract long position() throws IOException; |
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259 |
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260 /** |
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261 * Sets this channel's file position. |
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262 * |
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263 * <p> Setting the position to a value that is greater than the file's |
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264 * current size is legal but does not change the size of the file. A later |
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265 * attempt to read bytes at such a position will immediately return an |
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266 * end-of-file indication. A later attempt to write bytes at such a |
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267 * position will cause the file to be grown to accommodate the new bytes; |
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268 * the values of any bytes between the previous end-of-file and the |
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269 * newly-written bytes are unspecified. </p> |
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270 * |
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271 * @param newPosition |
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272 * The new position, a non-negative integer counting |
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273 * the number of bytes from the beginning of the file |
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274 * |
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275 * @return This file channel |
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276 * |
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277 * @throws ClosedChannelException |
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278 * If this channel is closed |
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279 * |
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280 * @throws IllegalArgumentException |
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281 * If the new position is negative |
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282 * |
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283 * @throws IOException |
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284 * If some other I/O error occurs |
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285 */ |
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286 public abstract FileChannel position(long newPosition) throws IOException; |
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287 |
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288 /** |
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289 * Returns the current size of this channel's file. </p> |
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290 * |
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291 * @return The current size of this channel's file, |
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292 * measured in bytes |
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293 * |
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294 * @throws ClosedChannelException |
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295 * If this channel is closed |
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296 * |
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297 * @throws IOException |
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298 * If some other I/O error occurs |
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299 */ |
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300 public abstract long size() throws IOException; |
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301 |
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302 /** |
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303 * Truncates this channel's file to the given size. |
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304 * |
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305 * <p> If the given size is less than the file's current size then the file |
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306 * is truncated, discarding any bytes beyond the new end of the file. If |
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307 * the given size is greater than or equal to the file's current size then |
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308 * the file is not modified. In either case, if this channel's file |
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309 * position is greater than the given size then it is set to that size. |
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310 * </p> |
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311 * |
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312 * @param size |
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313 * The new size, a non-negative byte count |
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314 * |
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315 * @return This file channel |
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316 * |
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317 * @throws NonWritableChannelException |
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318 * If this channel was not opened for writing |
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319 * |
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320 * @throws ClosedChannelException |
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321 * If this channel is closed |
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322 * |
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323 * @throws IllegalArgumentException |
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324 * If the new size is negative |
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325 * |
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326 * @throws IOException |
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327 * If some other I/O error occurs |
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328 */ |
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329 public abstract FileChannel truncate(long size) throws IOException; |
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330 |
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331 /** |
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332 * Forces any updates to this channel's file to be written to the storage |
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333 * device that contains it. |
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334 * |
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335 * <p> If this channel's file resides on a local storage device then when |
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336 * this method returns it is guaranteed that all changes made to the file |
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337 * since this channel was created, or since this method was last invoked, |
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338 * will have been written to that device. This is useful for ensuring that |
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339 * critical information is not lost in the event of a system crash. |
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340 * |
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341 * <p> If the file does not reside on a local device then no such guarantee |
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342 * is made. |
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343 * |
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344 * <p> The <tt>metaData</tt> parameter can be used to limit the number of |
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345 * I/O operations that this method is required to perform. Passing |
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346 * <tt>false</tt> for this parameter indicates that only updates to the |
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347 * file's content need be written to storage; passing <tt>true</tt> |
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348 * indicates that updates to both the file's content and metadata must be |
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349 * written, which generally requires at least one more I/O operation. |
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350 * Whether this parameter actually has any effect is dependent upon the |
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351 * underlying operating system and is therefore unspecified. |
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352 * |
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353 * <p> Invoking this method may cause an I/O operation to occur even if the |
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354 * channel was only opened for reading. Some operating systems, for |
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355 * example, maintain a last-access time as part of a file's metadata, and |
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356 * this time is updated whenever the file is read. Whether or not this is |
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357 * actually done is system-dependent and is therefore unspecified. |
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358 * |
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359 * <p> This method is only guaranteed to force changes that were made to |
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360 * this channel's file via the methods defined in this class. It may or |
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361 * may not force changes that were made by modifying the content of a |
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362 * {@link MappedByteBuffer </code>mapped byte buffer<code>} obtained by |
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363 * invoking the {@link #map map} method. Invoking the {@link |
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364 * MappedByteBuffer#force force} method of the mapped byte buffer will |
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365 * force changes made to the buffer's content to be written. </p> |
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366 * |
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367 * @param metaData |
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368 * If <tt>true</tt> then this method is required to force changes |
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369 * to both the file's content and metadata to be written to |
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370 * storage; otherwise, it need only force content changes to be |
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371 * written |
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372 * |
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373 * @throws ClosedChannelException |
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374 * If this channel is closed |
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375 * |
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376 * @throws IOException |
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377 * If some other I/O error occurs |
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378 */ |
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379 public abstract void force(boolean metaData) throws IOException; |
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380 |
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381 /** |
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382 * Transfers bytes from this channel's file to the given writable byte |
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383 * channel. |
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384 * |
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385 * <p> An attempt is made to read up to <tt>count</tt> bytes starting at |
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386 * the given <tt>position</tt> in this channel's file and write them to the |
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387 * target channel. An invocation of this method may or may not transfer |
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388 * all of the requested bytes; whether or not it does so depends upon the |
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389 * natures and states of the channels. Fewer than the requested number of |
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390 * bytes are transferred if this channel's file contains fewer than |
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391 * <tt>count</tt> bytes starting at the given <tt>position</tt>, or if the |
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392 * target channel is non-blocking and it has fewer than <tt>count</tt> |
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393 * bytes free in its output buffer. |
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394 * |
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395 * <p> This method does not modify this channel's position. If the given |
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396 * position is greater than the file's current size then no bytes are |
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397 * transferred. If the target channel has a position then bytes are |
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398 * written starting at that position and then the position is incremented |
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399 * by the number of bytes written. |
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400 * |
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401 * <p> This method is potentially much more efficient than a simple loop |
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402 * that reads from this channel and writes to the target channel. Many |
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403 * operating systems can transfer bytes directly from the filesystem cache |
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404 * to the target channel without actually copying them. </p> |
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405 * |
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406 * @param position |
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407 * The position within the file at which the transfer is to begin; |
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408 * must be non-negative |
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409 * |
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410 * @param count |
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411 * The maximum number of bytes to be transferred; must be |
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412 * non-negative |
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413 * |
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414 * @param target |
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415 * The target channel |
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416 * |
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417 * @return The number of bytes, possibly zero, |
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418 * that were actually transferred |
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419 * |
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420 * @throws IllegalArgumentException |
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421 * If the preconditions on the parameters do not hold |
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422 * |
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423 * @throws NonReadableChannelException |
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424 * If this channel was not opened for reading |
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425 * |
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426 * @throws NonWritableChannelException |
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427 * If the target channel was not opened for writing |
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428 * |
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429 * @throws ClosedChannelException |
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430 * If either this channel or the target channel is closed |
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431 * |
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432 * @throws AsynchronousCloseException |
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433 * If another thread closes either channel |
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434 * while the transfer is in progress |
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435 * |
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436 * @throws ClosedByInterruptException |
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437 * If another thread interrupts the current thread while the |
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438 * transfer is in progress, thereby closing both channels and |
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439 * setting the current thread's interrupt status |
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440 * |
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441 * @throws IOException |
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442 * If some other I/O error occurs |
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443 */ |
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444 public abstract long transferTo(long position, long count, |
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445 WritableByteChannel target) |
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446 throws IOException; |
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447 |
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448 /** |
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449 * Transfers bytes into this channel's file from the given readable byte |
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450 * channel. |
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451 * |
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452 * <p> An attempt is made to read up to <tt>count</tt> bytes from the |
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453 * source channel and write them to this channel's file starting at the |
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454 * given <tt>position</tt>. An invocation of this method may or may not |
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455 * transfer all of the requested bytes; whether or not it does so depends |
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456 * upon the natures and states of the channels. Fewer than the requested |
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457 * number of bytes will be transferred if the source channel has fewer than |
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458 * <tt>count</tt> bytes remaining, or if the source channel is non-blocking |
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459 * and has fewer than <tt>count</tt> bytes immediately available in its |
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460 * input buffer. |
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461 * |
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462 * <p> This method does not modify this channel's position. If the given |
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463 * position is greater than the file's current size then no bytes are |
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464 * transferred. If the source channel has a position then bytes are read |
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465 * starting at that position and then the position is incremented by the |
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466 * number of bytes read. |
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467 * |
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468 * <p> This method is potentially much more efficient than a simple loop |
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469 * that reads from the source channel and writes to this channel. Many |
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470 * operating systems can transfer bytes directly from the source channel |
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471 * into the filesystem cache without actually copying them. </p> |
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472 * |
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473 * @param src |
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474 * The source channel |
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475 * |
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476 * @param position |
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477 * The position within the file at which the transfer is to begin; |
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478 * must be non-negative |
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479 * |
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480 * @param count |
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481 * The maximum number of bytes to be transferred; must be |
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482 * non-negative |
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483 * |
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484 * @return The number of bytes, possibly zero, |
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485 * that were actually transferred |
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486 * |
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487 * @throws IllegalArgumentException |
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488 * If the preconditions on the parameters do not hold |
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489 * |
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490 * @throws NonReadableChannelException |
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491 * If the source channel was not opened for reading |
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492 * |
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493 * @throws NonWritableChannelException |
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494 * If this channel was not opened for writing |
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495 * |
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496 * @throws ClosedChannelException |
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497 * If either this channel or the source channel is closed |
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498 * |
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499 * @throws AsynchronousCloseException |
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500 * If another thread closes either channel |
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501 * while the transfer is in progress |
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502 * |
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503 * @throws ClosedByInterruptException |
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504 * If another thread interrupts the current thread while the |
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505 * transfer is in progress, thereby closing both channels and |
|
506 * setting the current thread's interrupt status |
|
507 * |
|
508 * @throws IOException |
|
509 * If some other I/O error occurs |
|
510 */ |
|
511 public abstract long transferFrom(ReadableByteChannel src, |
|
512 long position, long count) |
|
513 throws IOException; |
|
514 |
|
515 /** |
|
516 * Reads a sequence of bytes from this channel into the given buffer, |
|
517 * starting at the given file position. |
|
518 * |
|
519 * <p> This method works in the same manner as the {@link |
|
520 * #read(ByteBuffer)} method, except that bytes are read starting at the |
|
521 * given file position rather than at the channel's current position. This |
|
522 * method does not modify this channel's position. If the given position |
|
523 * is greater than the file's current size then no bytes are read. </p> |
|
524 * |
|
525 * @param dst |
|
526 * The buffer into which bytes are to be transferred |
|
527 * |
|
528 * @param position |
|
529 * The file position at which the transfer is to begin; |
|
530 * must be non-negative |
|
531 * |
|
532 * @return The number of bytes read, possibly zero, or <tt>-1</tt> if the |
|
533 * given position is greater than or equal to the file's current |
|
534 * size |
|
535 * |
|
536 * @throws IllegalArgumentException |
|
537 * If the position is negative |
|
538 * |
|
539 * @throws NonReadableChannelException |
|
540 * If this channel was not opened for reading |
|
541 * |
|
542 * @throws ClosedChannelException |
|
543 * If this channel is closed |
|
544 * |
|
545 * @throws AsynchronousCloseException |
|
546 * If another thread closes this channel |
|
547 * while the read operation is in progress |
|
548 * |
|
549 * @throws ClosedByInterruptException |
|
550 * If another thread interrupts the current thread |
|
551 * while the read operation is in progress, thereby |
|
552 * closing the channel and setting the current thread's |
|
553 * interrupt status |
|
554 * |
|
555 * @throws IOException |
|
556 * If some other I/O error occurs |
|
557 */ |
|
558 public abstract int read(ByteBuffer dst, long position) throws IOException; |
|
559 |
|
560 /** |
|
561 * Writes a sequence of bytes to this channel from the given buffer, |
|
562 * starting at the given file position. |
|
563 * |
|
564 * <p> This method works in the same manner as the {@link |
|
565 * #write(ByteBuffer)} method, except that bytes are written starting at |
|
566 * the given file position rather than at the channel's current position. |
|
567 * This method does not modify this channel's position. If the given |
|
568 * position is greater than the file's current size then the file will be |
|
569 * grown to accommodate the new bytes; the values of any bytes between the |
|
570 * previous end-of-file and the newly-written bytes are unspecified. </p> |
|
571 * |
|
572 * @param src |
|
573 * The buffer from which bytes are to be transferred |
|
574 * |
|
575 * @param position |
|
576 * The file position at which the transfer is to begin; |
|
577 * must be non-negative |
|
578 * |
|
579 * @return The number of bytes written, possibly zero |
|
580 * |
|
581 * @throws IllegalArgumentException |
|
582 * If the position is negative |
|
583 * |
|
584 * @throws NonWritableChannelException |
|
585 * If this channel was not opened for writing |
|
586 * |
|
587 * @throws ClosedChannelException |
|
588 * If this channel is closed |
|
589 * |
|
590 * @throws AsynchronousCloseException |
|
591 * If another thread closes this channel |
|
592 * while the write operation is in progress |
|
593 * |
|
594 * @throws ClosedByInterruptException |
|
595 * If another thread interrupts the current thread |
|
596 * while the write operation is in progress, thereby |
|
597 * closing the channel and setting the current thread's |
|
598 * interrupt status |
|
599 * |
|
600 * @throws IOException |
|
601 * If some other I/O error occurs |
|
602 */ |
|
603 public abstract int write(ByteBuffer src, long position) throws IOException; |
|
604 |
|
605 |
|
606 // -- Memory-mapped buffers -- |
|
607 |
|
608 /** |
|
609 * A typesafe enumeration for file-mapping modes. |
|
610 * |
|
611 * @since 1.4 |
|
612 * |
|
613 * @see java.nio.channels.FileChannel#map |
|
614 */ |
|
615 public static class MapMode { |
|
616 |
|
617 /** |
|
618 * Mode for a read-only mapping. |
|
619 */ |
|
620 public static final MapMode READ_ONLY |
|
621 = new MapMode("READ_ONLY"); |
|
622 |
|
623 /** |
|
624 * Mode for a read/write mapping. |
|
625 */ |
|
626 public static final MapMode READ_WRITE |
|
627 = new MapMode("READ_WRITE"); |
|
628 |
|
629 /** |
|
630 * Mode for a private (copy-on-write) mapping. |
|
631 */ |
|
632 public static final MapMode PRIVATE |
|
633 = new MapMode("PRIVATE"); |
|
634 |
|
635 private final String name; |
|
636 |
|
637 private MapMode(String name) { |
|
638 this.name = name; |
|
639 } |
|
640 |
|
641 /** |
|
642 * Returns a string describing this file-mapping mode. |
|
643 * |
|
644 * @return A descriptive string |
|
645 */ |
|
646 public String toString() { |
|
647 return name; |
|
648 } |
|
649 |
|
650 } |
|
651 |
|
652 /** |
|
653 * Maps a region of this channel's file directly into memory. |
|
654 * |
|
655 * <p> A region of a file may be mapped into memory in one of three modes: |
|
656 * </p> |
|
657 * |
|
658 * <ul type=disc> |
|
659 * |
|
660 * <li><p> <i>Read-only:</i> Any attempt to modify the resulting buffer |
|
661 * will cause a {@link java.nio.ReadOnlyBufferException} to be thrown. |
|
662 * ({@link MapMode#READ_ONLY MapMode.READ_ONLY}) </p></li> |
|
663 * |
|
664 * <li><p> <i>Read/write:</i> Changes made to the resulting buffer will |
|
665 * eventually be propagated to the file; they may or may not be made |
|
666 * visible to other programs that have mapped the same file. ({@link |
|
667 * MapMode#READ_WRITE MapMode.READ_WRITE}) </p></li> |
|
668 * |
|
669 * <li><p> <i>Private:</i> Changes made to the resulting buffer will not |
|
670 * be propagated to the file and will not be visible to other programs |
|
671 * that have mapped the same file; instead, they will cause private |
|
672 * copies of the modified portions of the buffer to be created. ({@link |
|
673 * MapMode#PRIVATE MapMode.PRIVATE}) </p></li> |
|
674 * |
|
675 * </ul> |
|
676 * |
|
677 * <p> For a read-only mapping, this channel must have been opened for |
|
678 * reading; for a read/write or private mapping, this channel must have |
|
679 * been opened for both reading and writing. |
|
680 * |
|
681 * <p> The {@link MappedByteBuffer </code>mapped byte buffer<code>} |
|
682 * returned by this method will have a position of zero and a limit and |
|
683 * capacity of <tt>size</tt>; its mark will be undefined. The buffer and |
|
684 * the mapping that it represents will remain valid until the buffer itself |
|
685 * is garbage-collected. |
|
686 * |
|
687 * <p> A mapping, once established, is not dependent upon the file channel |
|
688 * that was used to create it. Closing the channel, in particular, has no |
|
689 * effect upon the validity of the mapping. |
|
690 * |
|
691 * <p> Many of the details of memory-mapped files are inherently dependent |
|
692 * upon the underlying operating system and are therefore unspecified. The |
|
693 * behavior of this method when the requested region is not completely |
|
694 * contained within this channel's file is unspecified. Whether changes |
|
695 * made to the content or size of the underlying file, by this program or |
|
696 * another, are propagated to the buffer is unspecified. The rate at which |
|
697 * changes to the buffer are propagated to the file is unspecified. |
|
698 * |
|
699 * <p> For most operating systems, mapping a file into memory is more |
|
700 * expensive than reading or writing a few tens of kilobytes of data via |
|
701 * the usual {@link #read read} and {@link #write write} methods. From the |
|
702 * standpoint of performance it is generally only worth mapping relatively |
|
703 * large files into memory. </p> |
|
704 * |
|
705 * @param mode |
|
706 * One of the constants {@link MapMode#READ_ONLY READ_ONLY}, {@link |
|
707 * MapMode#READ_WRITE READ_WRITE}, or {@link MapMode#PRIVATE |
|
708 * PRIVATE} defined in the {@link MapMode} class, according to |
|
709 * whether the file is to be mapped read-only, read/write, or |
|
710 * privately (copy-on-write), respectively |
|
711 * |
|
712 * @param position |
|
713 * The position within the file at which the mapped region |
|
714 * is to start; must be non-negative |
|
715 * |
|
716 * @param size |
|
717 * The size of the region to be mapped; must be non-negative and |
|
718 * no greater than {@link java.lang.Integer#MAX_VALUE} |
|
719 * |
|
720 * @throws NonReadableChannelException |
|
721 * If the <tt>mode</tt> is {@link MapMode#READ_ONLY READ_ONLY} but |
|
722 * this channel was not opened for reading |
|
723 * |
|
724 * @throws NonWritableChannelException |
|
725 * If the <tt>mode</tt> is {@link MapMode#READ_WRITE READ_WRITE} or |
|
726 * {@link MapMode#PRIVATE PRIVATE} but this channel was not opened |
|
727 * for both reading and writing |
|
728 * |
|
729 * @throws IllegalArgumentException |
|
730 * If the preconditions on the parameters do not hold |
|
731 * |
|
732 * @throws IOException |
|
733 * If some other I/O error occurs |
|
734 * |
|
735 * @see java.nio.channels.FileChannel.MapMode |
|
736 * @see java.nio.MappedByteBuffer |
|
737 */ |
|
738 public abstract MappedByteBuffer map(MapMode mode, |
|
739 long position, long size) |
|
740 throws IOException; |
|
741 |
|
742 |
|
743 // -- Locks -- |
|
744 |
|
745 /** |
|
746 * Acquires a lock on the given region of this channel's file. |
|
747 * |
|
748 * <p> An invocation of this method will block until the region can be |
|
749 * locked, this channel is closed, or the invoking thread is interrupted, |
|
750 * whichever comes first. |
|
751 * |
|
752 * <p> If this channel is closed by another thread during an invocation of |
|
753 * this method then an {@link AsynchronousCloseException} will be thrown. |
|
754 * |
|
755 * <p> If the invoking thread is interrupted while waiting to acquire the |
|
756 * lock then its interrupt status will be set and a {@link |
|
757 * FileLockInterruptionException} will be thrown. If the invoker's |
|
758 * interrupt status is set when this method is invoked then that exception |
|
759 * will be thrown immediately; the thread's interrupt status will not be |
|
760 * changed. |
|
761 * |
|
762 * <p> The region specified by the <tt>position</tt> and <tt>size</tt> |
|
763 * parameters need not be contained within, or even overlap, the actual |
|
764 * underlying file. Lock regions are fixed in size; if a locked region |
|
765 * initially contains the end of the file and the file grows beyond the |
|
766 * region then the new portion of the file will not be covered by the lock. |
|
767 * If a file is expected to grow in size and a lock on the entire file is |
|
768 * required then a region starting at zero, and no smaller than the |
|
769 * expected maximum size of the file, should be locked. The zero-argument |
|
770 * {@link #lock()} method simply locks a region of size {@link |
|
771 * Long#MAX_VALUE}. |
|
772 * |
|
773 * <p> Some operating systems do not support shared locks, in which case a |
|
774 * request for a shared lock is automatically converted into a request for |
|
775 * an exclusive lock. Whether the newly-acquired lock is shared or |
|
776 * exclusive may be tested by invoking the resulting lock object's {@link |
|
777 * FileLock#isShared() isShared} method. |
|
778 * |
|
779 * <p> File locks are held on behalf of the entire Java virtual machine. |
|
780 * They are not suitable for controlling access to a file by multiple |
|
781 * threads within the same virtual machine. </p> |
|
782 * |
|
783 * @param position |
|
784 * The position at which the locked region is to start; must be |
|
785 * non-negative |
|
786 * |
|
787 * @param size |
|
788 * The size of the locked region; must be non-negative, and the sum |
|
789 * <tt>position</tt> + <tt>size</tt> must be non-negative |
|
790 * |
|
791 * @param shared |
|
792 * <tt>true</tt> to request a shared lock, in which case this |
|
793 * channel must be open for reading (and possibly writing); |
|
794 * <tt>false</tt> to request an exclusive lock, in which case this |
|
795 * channel must be open for writing (and possibly reading) |
|
796 * |
|
797 * @return A lock object representing the newly-acquired lock |
|
798 * |
|
799 * @throws IllegalArgumentException |
|
800 * If the preconditions on the parameters do not hold |
|
801 * |
|
802 * @throws ClosedChannelException |
|
803 * If this channel is closed |
|
804 * |
|
805 * @throws AsynchronousCloseException |
|
806 * If another thread closes this channel while the invoking |
|
807 * thread is blocked in this method |
|
808 * |
|
809 * @throws FileLockInterruptionException |
|
810 * If the invoking thread is interrupted while blocked in this |
|
811 * method |
|
812 * |
|
813 * @throws OverlappingFileLockException |
|
814 * If a lock that overlaps the requested region is already held by |
|
815 * this Java virtual machine, or if another thread is already |
|
816 * blocked in this method and is attempting to lock an overlapping |
|
817 * region |
|
818 * |
|
819 * @throws NonReadableChannelException |
|
820 * If <tt>shared</tt> is <tt>true</tt> this channel was not |
|
821 * opened for reading |
|
822 * |
|
823 * @throws NonWritableChannelException |
|
824 * If <tt>shared</tt> is <tt>false</tt> but this channel was not |
|
825 * opened for writing |
|
826 * |
|
827 * @throws IOException |
|
828 * If some other I/O error occurs |
|
829 * |
|
830 * @see #lock() |
|
831 * @see #tryLock() |
|
832 * @see #tryLock(long,long,boolean) |
|
833 */ |
|
834 public abstract FileLock lock(long position, long size, boolean shared) |
|
835 throws IOException; |
|
836 |
|
837 /** |
|
838 * Acquires an exclusive lock on this channel's file. |
|
839 * |
|
840 * <p> An invocation of this method of the form <tt>fc.lock()</tt> behaves |
|
841 * in exactly the same way as the invocation |
|
842 * |
|
843 * <pre> |
|
844 * fc.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) </pre> |
|
845 * |
|
846 * @return A lock object representing the newly-acquired lock |
|
847 * |
|
848 * @throws ClosedChannelException |
|
849 * If this channel is closed |
|
850 * |
|
851 * @throws AsynchronousCloseException |
|
852 * If another thread closes this channel while the invoking |
|
853 * thread is blocked in this method |
|
854 * |
|
855 * @throws FileLockInterruptionException |
|
856 * If the invoking thread is interrupted while blocked in this |
|
857 * method |
|
858 * |
|
859 * @throws OverlappingFileLockException |
|
860 * If a lock that overlaps the requested region is already held by |
|
861 * this Java virtual machine, or if another thread is already |
|
862 * blocked in this method and is attempting to lock an overlapping |
|
863 * region of the same file |
|
864 * |
|
865 * @throws NonWritableChannelException |
|
866 * If this channel was not opened for writing |
|
867 * |
|
868 * @throws IOException |
|
869 * If some other I/O error occurs |
|
870 * |
|
871 * @see #lock(long,long,boolean) |
|
872 * @see #tryLock() |
|
873 * @see #tryLock(long,long,boolean) |
|
874 */ |
|
875 public final FileLock lock() throws IOException { |
|
876 return lock(0L, Long.MAX_VALUE, false); |
|
877 } |
|
878 |
|
879 /** |
|
880 * Attempts to acquire a lock on the given region of this channel's file. |
|
881 * |
|
882 * <p> This method does not block. An invocation always returns |
|
883 * immediately, either having acquired a lock on the requested region or |
|
884 * having failed to do so. If it fails to acquire a lock because an |
|
885 * overlapping lock is held by another program then it returns |
|
886 * <tt>null</tt>. If it fails to acquire a lock for any other reason then |
|
887 * an appropriate exception is thrown. |
|
888 * |
|
889 * <p> The region specified by the <tt>position</tt> and <tt>size</tt> |
|
890 * parameters need not be contained within, or even overlap, the actual |
|
891 * underlying file. Lock regions are fixed in size; if a locked region |
|
892 * initially contains the end of the file and the file grows beyond the |
|
893 * region then the new portion of the file will not be covered by the lock. |
|
894 * If a file is expected to grow in size and a lock on the entire file is |
|
895 * required then a region starting at zero, and no smaller than the |
|
896 * expected maximum size of the file, should be locked. The zero-argument |
|
897 * {@link #tryLock()} method simply locks a region of size {@link |
|
898 * Long#MAX_VALUE}. |
|
899 * |
|
900 * <p> Some operating systems do not support shared locks, in which case a |
|
901 * request for a shared lock is automatically converted into a request for |
|
902 * an exclusive lock. Whether the newly-acquired lock is shared or |
|
903 * exclusive may be tested by invoking the resulting lock object's {@link |
|
904 * FileLock#isShared() isShared} method. |
|
905 * |
|
906 * <p> File locks are held on behalf of the entire Java virtual machine. |
|
907 * They are not suitable for controlling access to a file by multiple |
|
908 * threads within the same virtual machine. </p> |
|
909 * |
|
910 * @param position |
|
911 * The position at which the locked region is to start; must be |
|
912 * non-negative |
|
913 * |
|
914 * @param size |
|
915 * The size of the locked region; must be non-negative, and the sum |
|
916 * <tt>position</tt> + <tt>size</tt> must be non-negative |
|
917 * |
|
918 * @param shared |
|
919 * <tt>true</tt> to request a shared lock, |
|
920 * <tt>false</tt> to request an exclusive lock |
|
921 * |
|
922 * @return A lock object representing the newly-acquired lock, |
|
923 * or <tt>null</tt> if the lock could not be acquired |
|
924 * because another program holds an overlapping lock |
|
925 * |
|
926 * @throws IllegalArgumentException |
|
927 * If the preconditions on the parameters do not hold |
|
928 * |
|
929 * @throws ClosedChannelException |
|
930 * If this channel is closed |
|
931 * |
|
932 * @throws OverlappingFileLockException |
|
933 * If a lock that overlaps the requested region is already held by |
|
934 * this Java virtual machine, or if another thread is already |
|
935 * blocked in this method and is attempting to lock an overlapping |
|
936 * region of the same file |
|
937 * |
|
938 * @throws IOException |
|
939 * If some other I/O error occurs |
|
940 * |
|
941 * @see #lock() |
|
942 * @see #lock(long,long,boolean) |
|
943 * @see #tryLock() |
|
944 */ |
|
945 public abstract FileLock tryLock(long position, long size, boolean shared) |
|
946 throws IOException; |
|
947 |
|
948 /** |
|
949 * Attempts to acquire an exclusive lock on this channel's file. |
|
950 * |
|
951 * <p> An invocation of this method of the form <tt>fc.tryLock()</tt> |
|
952 * behaves in exactly the same way as the invocation |
|
953 * |
|
954 * <pre> |
|
955 * fc.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre> |
|
956 * |
|
957 * @return A lock object representing the newly-acquired lock, |
|
958 * or <tt>null</tt> if the lock could not be acquired |
|
959 * because another program holds an overlapping lock |
|
960 * |
|
961 * @throws ClosedChannelException |
|
962 * If this channel is closed |
|
963 * |
|
964 * @throws OverlappingFileLockException |
|
965 * If a lock that overlaps the requested region is already held by |
|
966 * this Java virtual machine, or if another thread is already |
|
967 * blocked in this method and is attempting to lock an overlapping |
|
968 * region |
|
969 * |
|
970 * @throws IOException |
|
971 * If some other I/O error occurs |
|
972 * |
|
973 * @see #lock() |
|
974 * @see #lock(long,long,boolean) |
|
975 * @see #tryLock(long,long,boolean) |
|
976 */ |
|
977 public final FileLock tryLock() throws IOException { |
|
978 return tryLock(0L, Long.MAX_VALUE, false); |
|
979 } |
|
980 |
|
981 } |