Apache Commons IO入門教程

讓我們來看看這里發生了什么，我們使用org.apache.commons.io.monitor包下的類創建了一個處理器來監聽一些特定的事件（在上面的例子中就是我們對文件或目錄所做的所有操作事件），為了獲得這些信息，我們需要做以下幾步操作：

1.3 過濾器

過濾器可以以組合的方式使用并且它的用途非常多樣。它可以輕松的區分不同的文件并且找到滿足我們條件的文件。我們可以組合不同的過濾器來執行文件的邏輯比較并且精確的獲取我們所需要文件，而無需使用冗余的字符串比較來尋找我們的文件。

FiltersExample.java

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:UsersLilykosworkspaceApacheCommonsExampleExampleFolder";

    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: example

1.4 比較器

使用org.apache.commons.io.comparator 包下的類可以讓你輕松的對文件或目錄進行比較或者排序。你只需提供一個文件列表，選擇不同的類就可以實現不同方式的文件比較。

ComparatorExample.java

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:UsersLilykosworkspaceApacheCommonsExampleExampleFolder";

    private static final String FILE_1 =
            "C:UsersLilykosworkspaceApacheCommonsExampleExampleFolderexample";

    private static final String FILE_2 =
            "C:UsersLilykosworkspaceApacheCommonsExampleExampleFolderexampleTxt.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:UsersLilykosworkspaceApacheCommonsExampleExampleFoldercomparator1.txt
    C:UsersLilykosworkspaceApacheCommonsExampleExampleFoldercomperator2.txt
    C:UsersLilykosworkspaceApacheCommonsExampleExampleFolderexample
    C:UsersLilykosworkspaceApacheCommonsExampleExampleFolderexampleFileEntry.txt
    C:UsersLilykosworkspaceApacheCommonsExampleExampleFolderexampleTxt.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

讓我們來看看這里用到了哪些類：

NameFileComparator：通過文件名來比較文件。

SizeFileComparator：通過文件大小來比較文件。

LastModifiedFileComparator：通過文件的最新修改時間來比較文件。

在這里你需要注意，比較可以在定的文件夾中（文件夾下的文件已經被sort()方法排序過了），也可以在兩個指定的文件之間（通過使用compare()方法）。

1.5 輸入

在org.apache.commons.io.input包下有許多InputStrem類的實現，我們來測試一個最實用的類，TeeInputStream，將InputStream以及OutputStream作為參數傳入其中，自動實現將輸入流的數據讀取到輸出流中。而且，通過傳入第三個參數，一個boolean類型參數，可以在數據讀取完畢之后自動關閉輸入流和輸出流。

InputExample.java

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:UsersLilykosworkspaceApacheCommonsExampleInputOutputExampleFolderweb.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.

1.6 輸出

與org.apache.commons.io.input包中的類相似， org.apache.commons.io.output包中同樣有OutputStream類的實現，他們可以在多種情況下使用，一個非常有意思的類就是 TeeOutputStream，它可以將輸出流進行分流，換句話說我們可以用一個輸入流將數據分別讀入到兩個不同的輸出流。

OutputExample.java

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.

2. 下載完整的示例