commons-io源码阅读心得
FileCleanTracker: 开启一个守护线程在后台默默的删除文件。
1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.io; 18 19 import java.io.File; 20 import java.lang.ref.PhantomReference; 21 import java.lang.ref.ReferenceQueue; 22 import java.util.Collection; 23 import java.util.Vector; 24 25 /** 26 * Keeps track of files awaiting deletion, and deletes them when an associated 27 * marker object is reclaimed by the garbage collector. 28 * <p> 29 * This utility creates a background thread to handle file deletion. 30 * Each file to be deleted is registered with a handler object. 31 * When the handler object is garbage collected, the file is deleted. 32 * <p> 33 * In an environment with multiple class loaders (a servlet container, for 34 * example), you should consider stopping the background thread if it is no 35 * longer needed. This is done by invoking the method 36 * {@link #exitWhenFinished}, typically in 37 * {@link javax.servlet.ServletContextListener#contextDestroyed} or similar. 38 * 39 * @author Noel Bergman 40 * @author Martin Cooper 41 * @version $Id: FileCleaner.java 490987 2006-12-29 12:11:48Z scolebourne $ 42 */ 43 public class FileCleaningTracker { 44 /** 45 * Queue of <code>Tracker</code> instances being watched. 46 */ 47 ReferenceQueue /* Tracker */ q = new ReferenceQueue(); 48 /** 49 * Collection of <code>Tracker</code> instances in existence. 50 */ 51 final Collection /* Tracker */ trackers = new Vector(); // synchronized 52 /** 53 * Whether to terminate the thread when the tracking is complete. 54 */ 55 volatile boolean exitWhenFinished = false; 56 /** 57 * The thread that will clean up registered files. 58 */ 59 Thread reaper; 60 61 //----------------------------------------------------------------------- 62 /** 63 * Track the specified file, using the provided marker, deleting the file 64 * when the marker instance is garbage collected. 65 * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used. 66 * 67 * @param file the file to be tracked, not null 68 * @param marker the marker object used to track the file, not null 69 * @throws NullPointerException if the file is null 70 */ 71 public void track(File file, Object marker) { 72 track(file, marker, (FileDeleteStrategy) null); 73 } 74 75 /** 76 * Track the specified file, using the provided marker, deleting the file 77 * when the marker instance is garbage collected. 78 * The speified deletion strategy is used. 79 * 80 * @param file the file to be tracked, not null 81 * @param marker the marker object used to track the file, not null 82 * @param deleteStrategy the strategy to delete the file, null means normal 83 * @throws NullPointerException if the file is null 84 */ 85 public void track(File file, Object marker, FileDeleteStrategy deleteStrategy) { 86 if (file == null) { 87 throw new NullPointerException("The file must not be null"); 88 } 89 addTracker(file.getPath(), marker, deleteStrategy); 90 } 91 92 /** 93 * Track the specified file, using the provided marker, deleting the file 94 * when the marker instance is garbage collected. 95 * The {@link FileDeleteStrategy#NORMAL normal} deletion strategy will be used. 96 * 97 * @param path the full path to the file to be tracked, not null 98 * @param marker the marker object used to track the file, not null 99 * @throws NullPointerException if the path is null 100 */ 101 public void track(String path, Object marker) { 102 track(path, marker, (FileDeleteStrategy) null); 103 } 104 105 /** 106 * Track the specified file, using the provided marker, deleting the file 107 * when the marker instance is garbage collected. 108 * The speified deletion strategy is used. 109 * 110 * @param path the full path to the file to be tracked, not null 111 * @param marker the marker object used to track the file, not null 112 * @param deleteStrategy the strategy to delete the file, null means normal 113 * @throws NullPointerException if the path is null 114 */ 115 public void track(String path, Object marker, FileDeleteStrategy deleteStrategy) { 116 if (path == null) { 117 throw new NullPointerException("The path must not be null"); 118 } 119 addTracker(path, marker, deleteStrategy); 120 } 121 122 /** 123 * Adds a tracker to the list of trackers. 124 * 125 * @param path the full path to the file to be tracked, not null 126 * @param marker the marker object used to track the file, not null 127 * @param deleteStrategy the strategy to delete the file, null means normal 128 */ 129 private synchronized void addTracker(String path, Object marker, FileDeleteStrategy deleteStrategy) { 130 // synchronized block protects reaper 131 if (exitWhenFinished) { 132 throw new IllegalStateException("No new trackers can be added once exitWhenFinished() is called"); 133 } 134 if (reaper == null) { 135 reaper = new Reaper(); 136 reaper.start(); 137 } 138 trackers.add(new Tracker(path, deleteStrategy, marker, q)); 139 } 140 141 //----------------------------------------------------------------------- 142 /** 143 * Retrieve the number of files currently being tracked, and therefore 144 * awaiting deletion. 145 * 146 * @return the number of files being tracked 147 */ 148 public int getTrackCount() { 149 return trackers.size(); 150 } 151 152 /** 153 * Call this method to cause the file cleaner thread to terminate when 154 * there are no more objects being tracked for deletion. 155 * <p> 156 * In a simple environment, you don't need this method as the file cleaner 157 * thread will simply exit when the JVM exits. In a more complex environment, 158 * with multiple class loaders (such as an application server), you should be 159 * aware that the file cleaner thread will continue running even if the class 160 * loader it was started from terminates. This can consitute a memory leak. 161 * <p> 162 * For example, suppose that you have developed a web application, which 163 * contains the commons-io jar file in your WEB-INF/lib directory. In other 164 * words, the FileCleaner class is loaded through the class loader of your 165 * web application. If the web application is terminated, but the servlet 166 * container is still running, then the file cleaner thread will still exist, 167 * posing a memory leak. 168 * <p> 169 * This method allows the thread to be terminated. Simply call this method 170 * in the resource cleanup code, such as {@link javax.servlet.ServletContextListener#contextDestroyed}. 171 * One called, no new objects can be tracked by the file cleaner. 172 */ 173 public synchronized void exitWhenFinished() { 174 // synchronized block protects reaper 175 exitWhenFinished = true; 176 if (reaper != null) { 177 synchronized (reaper) { 178 reaper.interrupt(); 179 } 180 } 181 } 182 183 //----------------------------------------------------------------------- 184 /** 185 * The reaper thread. 186 */ 187 private final class Reaper extends Thread { 188 /** Construct a new Reaper */ 189 Reaper() { 190 super("File Reaper"); 191 setPriority(Thread.MAX_PRIORITY); 192 setDaemon(true); 193 } 194 195 /** 196 * Run the reaper thread that will delete files as their associated 197 * marker objects are reclaimed by the garbage collector. 198 */ 199 public void run() { 200 // thread exits when exitWhenFinished is true and there are no more tracked objects 201 while (exitWhenFinished == false || trackers.size() > 0) { 202 Tracker tracker = null; 203 try { 204 // Wait for a tracker to remove. 205 tracker = (Tracker) q.remove(); 206 } catch (Exception e) { 207 continue; 208 } 209 if (tracker != null) { 210 tracker.delete(); 211 tracker.clear(); 212 trackers.remove(tracker); 213 } 214 } 215 } 216 } 217 218 //----------------------------------------------------------------------- 219 /** 220 * Inner class which acts as the reference for a file pending deletion. 221 */ 222 private static final class Tracker extends PhantomReference { 223 224 /** 225 * The full path to the file being tracked. 226 */ 227 private final String path; 228 /** 229 * The strategy for deleting files. 230 */ 231 private final FileDeleteStrategy deleteStrategy; 232 233 /** 234 * Constructs an instance of this class from the supplied parameters. 235 * 236 * @param path the full path to the file to be tracked, not null 237 * @param deleteStrategy the strategy to delete the file, null means normal 238 * @param marker the marker object used to track the file, not null 239 * @param queue the queue on to which the tracker will be pushed, not null 240 */ 241 Tracker(String path, FileDeleteStrategy deleteStrategy, Object marker, ReferenceQueue queue) { 242 super(marker, queue); 243 this.path = path; 244 this.deleteStrategy = (deleteStrategy == null ? FileDeleteStrategy.NORMAL : deleteStrategy); 245 } 246 247 /** 248 * Deletes the file associated with this tracker instance. 249 * 250 * @return <code>true</code> if the file was deleted successfully; 251 * <code>false</code> otherwise. 252 */ 253 public boolean delete() { 254 return deleteStrategy.deleteQuietly(new File(path)); 255 } 256 } 257 258 }
IOUtils: 通用的io工具类。
主要有：
toByteArray(InputStream/Reader/String)方法：将输入流拷贝到相应的输出流，然后调用输出流的toByteArray()方法返回；
toCharArray(InputStream/Reader)方法：将输入流拷贝到相应的输出流，然后调用输出流的toCharArray()方法返回；
toString(InputStream/Reader/byte[])方法：将输入流拷贝到StringWriter，然后调用StringWriter.toString()方法返回；
readLines(InputStream/Reader)方法：将输入流中的每一行存入list容器中，然后返回list;
contentEquals(InputStream/Reader)方法：比较俩个输入流的内容是否一致;
CopyUtils: 拷贝输入流内容到输出流的工具类。
FileUtils: 通用的文件工具类。
FileSystemUtils: 通用的文件系统工具类。
freeSpaceKb(String path)方法： 获取系统(windows/unix)下的某个路径下的空间值，单位KB。通过执行命令：'dir /-c' on Windows and 'df' on *nix.
FilenameUtils: 通用的文件名和文件路径工具类。
normalize(String filename)方法：格式化文件名；
getPrefixLength(String filename)方法：获取文件名前缀的长度；
getPrefix(String filename)方法：获取文件名前缀；
getPath(String filename)方法：获取文件名路径；
getPathNoEndSeparator(String filename)方法：获取文件名路径不带最后分隔符；
getFullPath(String filename)方法：获取文件名对应的全路径；
wildcardMatch(String filename, String wildcardMatcher)方法：文件名与某个通配符字符串是否匹配；
一系列的FileFilter，都继承了AbstractFileFilter，它实现了IOFileFilter，IOFileFilter继承了FileFilter和FilenameFilter。
如：AgeFileFilter 可以过滤某些早于、等于或者晚于某个时间的文件或文件列表。
1 File dir = new File("."); 2 // We are interested in files older than one day 3 long cutoff = System.currentTimeMillis() - (24 * 60 * 60 * 1000); 4 String[] files = dir.list( new AgeFileFilter(cutoff) ); 5 for ( int i = 0; i < files.length; i++ ) { 6 System.out.println(files[i]); 7 }
AndFileFilter 将几个其它的文件过滤器做逻辑与操作，可以获取符合这几个文件过滤器的文件或文件列表。
WildcardFileFilter 文件通配符过滤器，可以获取文件名匹配某个设定的通配符的文件。
1 File dir = new File("."); 2 FileFilter fileFilter = new WildcardFileFilter("*test*.java~*~"); 3 File[] files = dir.listFiles(fileFilter); 4 for (int i = 0; i < files.length; i++) { 5 System.out.println(files[i]); 6 }
一系列的IO output/input类：
如：CountingInputStream 可以记录输入流读取的字节数；
ByteArrayOutputStream 将输出流的数据写到字节数组中；
CountingOutputStream 记录输出流输出的字节数。