Apache Commons IO是由Apache Foundation維護的java庫，它提供了多種類庫使開發者能夠很容易地完成一些常見的任務，簡化那些被反覆的樣板化的代碼。這個類庫的重要性是巨大的，因爲它非常成熟，並且由有經驗的開發者維護，他們會考慮到各種情形，和修復他們遇到的不同種類的bug。
下面會展示org.apache.commons.io包的幾個不同功能，下面的代碼會分成以下幾類，每一類都表示Apache Commons IO所覆蓋的領域，這些領域包括：
- Utility classes
- Input
- Output
- Filters
- Comparators
- File Monitor
Utility classes
在org.apache.commons.io中有不同的工具類，幾種大多數跟文件操作和字符串比較相關，下面給出最重要的幾個：
- FilenameUtils：這個類主要處理文件名， 在Unix和Windows上同樣適用；
- FileUtils： 提供了文件操作的方法（移動、打開和讀取、檢查文件是否存在等）；
- IOCase： 字符串的操作和比較；
- FileSystemUtils：它的方法主要返回指定驅動的空閒空間；
Utility代碼示例：
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);
}
}輸出：
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): 31395File Monitor
org.apache.commons.io.monitor包含了獲取文件的特定信息，但是更重要的是它能夠創建handlers，用於最終特定文件或文件夾的變化，示例如下：
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();
}
}
}輸出：
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在這裏我們使用org.apache.commons.io.monitor包創建了handlers用來監聽特定的事件，爲了實現該目標，主要有一下幾步：
- 創建File對象，然後應用到想要監聽的目錄上；
- 創建FileAlterationObserver對象，它負責觀察這些變化；
- 使用addListener()方法添加FileAlterationListenerAdaptor觀察者；
- 創建FileAlterationMonitor並添加觀察者；
- 使用start()方法啓動monitor，必要的時候使用stop()方法終止它。
Filters
Filters主要用於不同文件的區分，得到滿足特定條件的文件。而且也可以聯合多個filters執行邏輯比較，獲取更加精準的文件類型。
Filters 示例：
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);
}
}
}輸出：
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: exampleComparators
org.apache.commons.io.comparator包用於簡單比較和排序文件和目錄。
Comparators示例：
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()));
}
}輸出：
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 2014Input
在org.apache.commons.io.input包中有多種對InputStream的實現。下面給出一個最實用的TeeInputStream，利用InputStream和OutputStream的參數自動拷貝輸入讀取的字節到輸出。而且使用第三個boolean參數，用來最終關閉TeeInputStream，InputStream和OutputStream。
Input示例：
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(); }
}
}
}輸出：
Input example...
XML encoding: UTF-8
Output stream: This should go to the output.Output
與org.apache.commons.io.input類似，org.apache.commons.io.output 實現了OutputStream，用於不同的場景。TeeOutputStream允許輸出流進行分支，也就是把一個輸入流發送到兩個不同的輸出流上。
Output示例：
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(); }
}
}
}輸出：
Output example...
Output stream 1: This should go to the output.
Output stream 2: This should go to the output.