原文参考 

http://www.javacodegeeks.com/2014/10/apache-commons-io-tutorial.html 

  Apache Commons IO 包绝对是好东西，地址在http://commons.apache.org/proper/commons-io/，下面用例子分别介绍： 

  1）  工具类 

  2） 输入 

  3） 输出 

  4） filters过滤 

  5） Comparators 

  6） 文件监控 

  

   总的入口例子为： 

  

 public class ApacheCommonsExampleMain {

     public static void main(String[] args) {
         UtilityExample.runExample();

         FileMonitorExample.runExample();

         FiltersExample.runExample();

         InputExample.runExample();

         OutputExample.runExample();

         ComparatorExample.runExample();
     }
 }

一  工具类包UtilityExample代码： 

    这个工具类包分如下几个主要工具类： 

     1） FilenameUtils:主要处理各种操作系统下对文件名的操作 

     2) FileUtils:处理文件的打开，移动，读取和判断文件是否存在 

    3） IOCASE：字符串的比较 

    4） FileSystemUtils:返回磁盘的空间大小 

   

 import java.io.File;
 import java.io.IOException;

 import org.apache.commons.io.FileSystemUtils;
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.FilenameUtils;
 import org.apache.commons.io.LineIterator;
 import org.apache.commons.io.IOCase;

 public final class UtilityExample {

     // We are using the file exampleTxt.txt in the folder ExampleFolder,
     // and we need to provide the full path to the Utility classes.
     private static final String EXAMPLE_TXT_PATH =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder\\exampleTxt.txt";

     private static final String PARENT_DIR =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample";

     public static void runExample() throws IOException {
         System.out.println("Utility Classes example...");


         // FilenameUtils

         System.out.println("Full path of exampleTxt: " +
                 FilenameUtils.getFullPath(EXAMPLE_TXT_PATH));

         System.out.println("Full name of exampleTxt: " +
                 FilenameUtils.getName(EXAMPLE_TXT_PATH));

         System.out.println("Extension of exampleTxt: " +
                 FilenameUtils.getExtension(EXAMPLE_TXT_PATH));

         System.out.println("Base name of exampleTxt: " +
                 FilenameUtils.getBaseName(EXAMPLE_TXT_PATH));


         // FileUtils

         // We can create a new File object using FileUtils.getFile(String)
         // and then use this object to get information from the file.
         File exampleFile = FileUtils.getFile(EXAMPLE_TXT_PATH);
         LineIterator iter = FileUtils.lineIterator(exampleFile);

         System.out.println("Contents of exampleTxt...");
         while (iter.hasNext()) {
             System.out.println("\t" + iter.next());
         }
         iter.close();

         // We can check if a file exists somewhere inside a certain directory.
         File parent = FileUtils.getFile(PARENT_DIR);
         System.out.println("Parent directory contains exampleTxt file: " +
                 FileUtils.directoryContains(parent, exampleFile));


         // IOCase

         String str1 = "This is a new String.";
         String str2 = "This is another new String, yes!";

         System.out.println("Ends with string (case sensitive): " +
                 IOCase.SENSITIVE.checkEndsWith(str1, "string."));
         System.out.println("Ends with string (case insensitive): " +
                 IOCase.INSENSITIVE.checkEndsWith(str1, "string."));

         System.out.println("String equality: " +
                 IOCase.SENSITIVE.checkEquals(str1, str2));


         // FileSystemUtils
         System.out.println("Free disk space (in KB): " + FileSystemUtils.freeSpaceKb("C:"));
         System.out.println("Free disk space (in MB): " + FileSystemUtils.freeSpaceKb("C:") / 1024);
     }
 }

输出： 

 Utility Classes example...
 Full path of exampleTxt: C:\Users\Lilykos\workspace\ApacheCommonsExample\ExampleFolder\
 Full name of exampleTxt: exampleTxt.txt
 Extension of exampleTxt: txt
 Base name of exampleTxt: exampleTxt
 Contents of exampleTxt...
     This is an example text file.
     We will use it for experimenting with Apache Commons IO.
 Parent directory contains exampleTxt file: true
 Ends with string (case sensitive): false
 Ends with string (case insensitive): true
 String equality: false
 Free disk space (in KB): 32149292
 Free disk space (in MB): 31395

二  FileMonitor工具类包 

   这个org.apache.commons.io.monitor 包中的工具类可以监视文件或者目录的变化，获得指定文件或者目录的相关信息，下面看例子： 

  

 import java.io.File;
 import java.io.IOException;

 import org.apache.commons.io.FileDeleteStrategy;
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.monitor.FileAlterationListenerAdaptor;
 import org.apache.commons.io.monitor.FileAlterationMonitor;
 import org.apache.commons.io.monitor.FileAlterationObserver;
 import org.apache.commons.io.monitor.FileEntry;


 public final class FileMonitorExample {

     private static final String EXAMPLE_PATH =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder\\exampleFileEntry.txt";

     private static final String PARENT_DIR =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder";

     private static final String NEW_DIR =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder\\newDir";

     private static final String NEW_FILE =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder\\newFile.txt";

     public static void runExample() {
         System.out.println("File Monitor example...");


         // FileEntry

         // We can monitor changes and get information about files
         // using the methods of this class.
         FileEntry entry = new FileEntry(FileUtils.getFile(EXAMPLE_PATH));

         System.out.println("File monitored: " + entry.getFile());
         System.out.println("File name: " + entry.getName());
         System.out.println("Is the file a directory?: " + entry.isDirectory());


         // File Monitoring

         // Create a new observer for the folder and add a listener
         // that will handle the events in a specific directory and take action.
         File parentDir = FileUtils.getFile(PARENT_DIR);

         FileAlterationObserver observer = new FileAlterationObserver(parentDir);
         observer.addListener(new FileAlterationListenerAdaptor() {

                 @Override
                 public void onFileCreate(File file) {
                     System.out.println("File created: " + file.getName());
                 }

                 @Override
                 public void onFileDelete(File file) {
                     System.out.println("File deleted: " + file.getName());
                 }

                 @Override
                 public void onDirectoryCreate(File dir) {
                     System.out.println("Directory created: " + dir.getName());
                 }

                 @Override
                 public void onDirectoryDelete(File dir) {
                     System.out.println("Directory deleted: " + dir.getName());
                 }
         });

         // Add a monior that will check for events every x ms,
         // and attach all the different observers that we want.
         FileAlterationMonitor monitor = new FileAlterationMonitor(500, observer);
         try {
             monitor.start();

             // After we attached the monitor, we can create some files and directories
             // and see what happens!
             File newDir = new File(NEW_DIR);
             File newFile = new File(NEW_FILE);

             newDir.mkdirs();
             newFile.createNewFile();

             Thread.sleep(1000);

             FileDeleteStrategy.NORMAL.delete(newDir);
             FileDeleteStrategy.NORMAL.delete(newFile);

             Thread.sleep(1000);

             monitor.stop();
         } catch (IOException e) {
             e.printStackTrace();
         } catch (InterruptedException e) {
             e.printStackTrace();
         } catch (Exception e) {
             e.printStackTrace();
         }
     }
 }

输出如下： 

  

 File Monitor example...
 File monitored: C:\Users\Lilykos\workspace\ApacheCommonsExample\ExampleFolder\exampleFileEntry.txt
 File name: exampleFileEntry.txt
 Is the file a directory?: false
 Directory created: newDir
 File created: newFile.txt
 Directory deleted: newDir
 File deleted: newFile.txt

    上面的特性的确很赞！分析下，这个工具类包下的工具类，可以允许我们创建跟踪文件或目录变化的监听句柄，当文件目录等发生任何变化，都可以用“观察者”的身份进行观察， 

其步骤如下： 

   1） 创建要监听的文件对象 

   2） 创建FileAlterationObserver 监听对象，在上面的例子中， 

   File parentDir = FileUtils.getFile(PARENT_DIR); 

  FileAlterationObserver observer = new FileAlterationObserver(parentDir); 

   创建的是监视parentDir目录的变化， 

   3） 为观察器创建FileAlterationListenerAdaptor的内部匿名类，增加对文件及目录的增加删除的监听 

   4） 创建FileAlterationMonitor监听类，每隔500ms监听目录下的变化，其中开启监视是用monitor的start方法即可。 

三  过滤器 filters 

   先看例子： 

  

 import java.io.File;

 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.IOCase;
 import org.apache.commons.io.filefilter.AndFileFilter;
 import org.apache.commons.io.filefilter.NameFileFilter;
 import org.apache.commons.io.filefilter.NotFileFilter;
 import org.apache.commons.io.filefilter.OrFileFilter;
 import org.apache.commons.io.filefilter.PrefixFileFilter;
 import org.apache.commons.io.filefilter.SuffixFileFilter;
 import org.apache.commons.io.filefilter.WildcardFileFilter;

 public final class FiltersExample {

     private static final String PARENT_DIR =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder";

     public static void runExample() {
         System.out.println("File Filter example...");


         // NameFileFilter
         // Right now, in the parent directory we have 3 files:
         //      directory example
         //      file exampleEntry.txt
         //      file exampleTxt.txt

         // Get all the files in the specified directory
         // that are named "example".
         File dir = FileUtils.getFile(PARENT_DIR);
         String[] acceptedNames = {        "example", "exampleTxt.txt"};
         for (String file: dir.list(new NameFileFilter(acceptedNames, IOCase.INSENSITIVE))) {
             System.out.println("File found, named: " + file);
         }


         //WildcardFileFilter
         // We can use wildcards in order to get less specific results
         //      ? used for 1 missing char
         //      * used for multiple missing chars
         for (String file: dir.list(new WildcardFileFilter("*ample*"))) {
             System.out.println("Wildcard file found, named: " + file);
         }


         // PrefixFileFilter
         // We can also use the equivalent of startsWith
         // for filtering files.
         for (String file: dir.list(new PrefixFileFilter("example"))) {
             System.out.println("Prefix file found, named: " + file);
         }


         // SuffixFileFilter
         // We can also use the equivalent of endsWith
         // for filtering files.
         for (String file: dir.list(new SuffixFileFilter(".txt"))) {
             System.out.println("Suffix file found, named: " + file);
         }


         // OrFileFilter
         // We can use some filters of filters.
         // in this case, we use a filter to apply a logical
         // or between our filters.
         for (String file: dir.list(new OrFileFilter(
                 new WildcardFileFilter("*ample*"), new SuffixFileFilter(".txt")))) {
             System.out.println("Or file found, named: " + file);
         }

         // And this can become very detailed.
         // Eg, get all the files that have "ample" in their name
         // but they are not text files (so they have no ".txt" extension.
         for (String file: dir.list(new AndFileFilter( // we will match 2 filters...
                 new WildcardFileFilter("*ample*"), // ...the 1st is a wildcard...
                 new NotFileFilter(new SuffixFileFilter(".txt"))))) { // ...and the 2nd is NOT .txt.
             System.out.println("And/Not file found, named: " + file);
         }
     }
 }

      可以看清晰看到，使用过滤器，可以分别在指定的目录下，寻找符合条件 

的文件，比如以什么开头的文件名，支持通配符，甚至支持多个过滤器进行或的操作！ 

  输出如下： 

 

 File Filter example...
 File found, named: example
 File found, named: exampleTxt.txt
 Wildcard file found, named: example
 Wildcard file found, named: exampleFileEntry.txt
 Wildcard file found, named: exampleTxt.txt
 Prefix file found, named: example
 Prefix file found, named: exampleFileEntry.txt
 Prefix file found, named: exampleTxt.txt
 Suffix file found, named: exampleFileEntry.txt
 Suffix file found, named: exampleTxt.txt
 Or file found, named: example
 Or file found, named: exampleFileEntry.txt
 Or file found, named: exampleTxt.txt
 And/Not file found, named: example

四  Comparators比较器 

   org.apache.commons.io.comparator包下的工具类，可以方便进行文件的比较： 

 import java.io.File;
 import java.util.Date;

 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.IOCase;
 import org.apache.commons.io.comparator.LastModifiedFileComparator;
 import org.apache.commons.io.comparator.NameFileComparator;
 import org.apache.commons.io.comparator.SizeFileComparator;

 public final class ComparatorExample {

     private static final String PARENT_DIR =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder";

     private static final String FILE_1 =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder\\example";

     private static final String FILE_2 =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\ExampleFolder\\exampleTxt.txt";

     public static void runExample() {
         System.out.println("Comparator example...");

         //NameFileComparator

         // Let's get a directory as a File object
         // and sort all its files.
         File parentDir = FileUtils.getFile(PARENT_DIR);
         NameFileComparator comparator = new NameFileComparator(IOCase.SENSITIVE);
         File[] sortedFiles = comparator.sort(parentDir.listFiles());

         System.out.println("Sorted by name files in parent directory: ");
         for (File file: sortedFiles) {
             System.out.println("\t"+ file.getAbsolutePath());
         }


         // SizeFileComparator

         // We can compare files based on their size.
         // The boolean in the constructor is about the directories.
         //      true: directory's contents count to the size.
         //      false: directory is considered zero size.
         SizeFileComparator sizeComparator = new SizeFileComparator(true);
         File[] sizeFiles = sizeComparator.sort(parentDir.listFiles());

         System.out.println("Sorted by size files in parent directory: ");
         for (File file: sizeFiles) {
             System.out.println("\t"+ file.getName() + " with size (kb): " + file.length());
         }


         // LastModifiedFileComparator

         // We can use this class to find which file was more recently modified.
         LastModifiedFileComparator lastModified = new LastModifiedFileComparator();
         File[] lastModifiedFiles = lastModified.sort(parentDir.listFiles());

         System.out.println("Sorted by last modified files in parent directory: ");
         for (File file: lastModifiedFiles) {
             Date modified = new Date(file.lastModified());
             System.out.println("\t"+ file.getName() + " last modified on: " + modified);
         }

         // Or, we can also compare 2 specific files and find which one was last modified.
         //      returns > 0 if the first file was last modified.
         //      returns  0)
             System.out.println("File " + file1.getName() + " was modified last because...");
         else
             System.out.println("File " + file2.getName() + "was modified last because...");

         System.out.println("\t"+ file1.getName() + " last modified on: " +
                 new Date(file1.lastModified()));
         System.out.println("\t"+ file2.getName() + " last modified on: " +
                 new Date(file2.lastModified()));
     }
 }

   输出如下： 

 Comparator example...
 Sorted by name files in parent directory:
     C:\Users\Lilykos\workspace\ApacheCommonsExample\ExampleFolder\comparator1.txt
     C:\Users\Lilykos\workspace\ApacheCommonsExample\ExampleFolder\comperator2.txt
     C:\Users\Lilykos\workspace\ApacheCommonsExample\ExampleFolder\example
     C:\Users\Lilykos\workspace\ApacheCommonsExample\ExampleFolder\exampleFileEntry.txt
     C:\Users\Lilykos\workspace\ApacheCommonsExample\ExampleFolder\exampleTxt.txt
 Sorted by size files in parent directory:
     example with size (kb): 0
     exampleTxt.txt with size (kb): 87
     exampleFileEntry.txt with size (kb): 503
     comperator2.txt with size (kb): 1458
     comparator1.txt with size (kb): 4436
 Sorted by last modified files in parent directory:
     exampleTxt.txt last modified on: Sun Oct 26 14:02:22 EET 2014
     example last modified on: Sun Oct 26 23:42:55 EET 2014
     comparator1.txt last modified on: Tue Oct 28 14:48:28 EET 2014
     comperator2.txt last modified on: Tue Oct 28 14:48:52 EET 2014
     exampleFileEntry.txt last modified on: Tue Oct 28 14:53:50 EET 2014
 File example was modified last because...
     example last modified on: Sun Oct 26 23:42:55 EET 2014
     exampleTxt.txt last modified on: Sun Oct 26 14:02:22 EET 2014

    可以看到，在上面的代码中 

NameFileComparator: 文件名的比较器，可以进行文件名称排序； 

SizeFileComparator: 按照文件大小比较 

LastModifiedFileComparator: 根据最新修改日期比较 

五  input包 

    在 common io的org.apache.commons.io.input 包中，有各种对InputStream的实现类： 

我们看下其中的TeeInputStream, ，它接受InputStream和Outputstream参数，例子如下： 

  

 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;

 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.input.TeeInputStream;
 import org.apache.commons.io.input.XmlStreamReader;


 public final class InputExample {

     private static final String XML_PATH =
             "C:\\Users\\Lilykos\\workspace\\ApacheCommonsExample\\InputOutputExampleFolder\\web.xml";

     private static final String INPUT = "This should go to the output.";

     public static void runExample() {
         System.out.println("Input example...");
         XmlStreamReader xmlReader = null;
         TeeInputStream tee = null;

         try {

             // XmlStreamReader

             // We can read an xml file and get its encoding.
             File xml = FileUtils.getFile(XML_PATH);

             xmlReader = new XmlStreamReader(xml);
             System.out.println("XML encoding: " + xmlReader.getEncoding());


             // TeeInputStream

             // This very useful class copies an input stream to an output stream
             // and closes both using only one close() method (by defining the 3rd
             // constructor parameter as true).
             ByteArrayInputStream in = new ByteArrayInputStream(INPUT.getBytes("US-ASCII"));
             ByteArrayOutputStream out = new ByteArrayOutputStream();

             tee = new TeeInputStream(in, out, true);
             tee.read(new byte[INPUT.length()]);

             System.out.println("Output stream: " + out.toString());
         } catch (IOException e) {
             e.printStackTrace();
         } finally {
             try { xmlReader.close(); }
             catch (IOException e) { e.printStackTrace(); }

             try { tee.close(); }
             catch (IOException e) { e.printStackTrace(); }
         }
     }
 }

输出： 

  

 Input example...
 XML encoding: UTF-8
 Output stream: This should go to the output.

   tee = new TeeInputStream(in, out, true); 

   中，分别三个参数，将输入流的内容输出到输出流，true参数为最后关闭流 

六 output工具类包 

  

  其中的org.apache.commons.io.output 是实现了outputstream,其中好特别的是 

TeeOutputStream能将一个输入流分别输出到两个输出流 

  

 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;

 import org.apache.commons.io.input.TeeInputStream;
 import org.apache.commons.io.output.TeeOutputStream;

 public final class OutputExample {

     private static final String INPUT = "This should go to the output.";

     public static void runExample() {
         System.out.println("Output example...");
         TeeInputStream teeIn = null;
         TeeOutputStream teeOut = null;

         try {

             // TeeOutputStream

             ByteArrayInputStream in = new ByteArrayInputStream(INPUT.getBytes("US-ASCII"));
             ByteArrayOutputStream out1 = new ByteArrayOutputStream();
             ByteArrayOutputStream out2 = new ByteArrayOutputStream();

             teeOut = new TeeOutputStream(out1, out2);
             teeIn = new TeeInputStream(in, teeOut, true);
             teeIn.read(new byte[INPUT.length()]);

             System.out.println("Output stream 1: " + out1.toString());
             System.out.println("Output stream 2: " + out2.toString());

         } catch (IOException e) {
             e.printStackTrace();
         } finally {
             // No need to close teeOut. When teeIn closes, it will also close its
             // Output stream (which is teeOut), which will in turn close the 2
             // branches (out1, out2).
             try { teeIn.close(); }
             catch (IOException e) { e.printStackTrace(); }
         }
     }
 }

  输出： 

 Output example...
 Output stream 1: This should go to the output.
 Output stream 2: This should go to the output.