Apache Commons IO簡介

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雖然Google的guava對Java的IO操作進行了一定封裝，但是它更偏向於集合、並發和緩衝，在實際項目中，我非常喜歡guava，同時我也非常喜歡Apache的一個工具包org.apache.commons.io，這兩個工具包提供非常強大的工具能力，能夠簡化代碼邏輯，提高開發效率和品質，是每個Java程式員都應該掌握的工具包。此文簡單介紹一下org.apache.commons.io，詳細的可參考其API注，此文絕大部分內容翻譯自http://www.javacodegeeks.com/2014/10/apache-commons-io-tutorial.html，感興趣的查看原文，本文源碼請移步

Apache Commons IO是Apache開源的一個工具包，其封裝了對IO的常見操作，使開發人員只需要少量的代碼就能完成大量的IO操作，此文主要介紹如下幾個工具類

• Utility classes
• Input
• Output
• Filters
• Comparators
• File Monitor

目前org.apache.commons.io2.4版本並未託管到Maven庫，所以需要自行下載然後將下載的commons-io-2.4.jar添加到環境變數中

1、Utils（FileUtils，FilenameUtils，FileSystemUtils）這三個類主要提供了對檔案、檔案名稱及檔案系統的操作，API非常簡單，通過API名稱都能知道其作用，

樣本如下

 //檔案絕對路徑    private static final String EXAMPLE_TXT_PATH =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio/commonio.txt";    //檔案父目錄    private static final String PARENT_DIR =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio";    public static void runExample() throws IOException {        System.out.println("Utility Classes example...");                        // FilenameUtils類樣本        //擷取完整路徑        System.out.println("Full path of exampleTxt: " +                FilenameUtils.getFullPath(EXAMPLE_TXT_PATH));        //擷取名稱        System.out.println("Full name of exampleTxt: " +                FilenameUtils.getName(EXAMPLE_TXT_PATH));      //擷取副檔名        System.out.println("Extension of exampleTxt: " +                FilenameUtils.getExtension(EXAMPLE_TXT_PATH));                System.out.println("Base name of exampleTxt: " +                FilenameUtils.getBaseName(EXAMPLE_TXT_PATH));                        // FileUtils類樣本                // 通過FileUtils.getFile(String)建立File對象，然後根據FileUtils.lineIterator(File)        //擷取行迭代器        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();                // 目錄是否已經包含檔案        File parent = FileUtils.getFile(PARENT_DIR);        System.out.println("Parent directory contains exampleTxt file: " +                FileUtils.directoryContains(parent, exampleFile));                        // IOCase類樣本                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類樣本        System.out.println("Free disk space (in KB): " + FileSystemUtils.freeSpaceKb("/Users"));        System.out.println("Free disk space (in MB): " + FileSystemUtils.freeSpaceKb("/Users") / 1024);    }

2、InputStream，其提供了XmlStreamReader工具類，能夠擷取xml的檔案編碼等操作，

樣本如下

private static final String XML_PATH =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio/test.xml";        public static void runExample() {        System.out.println("Input example...");        XmlStreamReader xmlReader = null;        try {                        // XmlStreamReader:讀取一個xml檔案，提供了過去檔案編碼API            File xml = FileUtils.getFile(XML_PATH);            xmlReader = new XmlStreamReader(xml);            System.out.println("XML encoding: " + xmlReader.getEncoding());        } catch (IOException e) {            e.printStackTrace();        } finally {            try { xmlReader.close(); }            catch (IOException e) { e.printStackTrace(); }        }    }

3、Output，其提供的TeeInputStream，TeeOutputStream類能將輸入資料流快速拷貝到輸出資料流中

private static final String INPUT = "This should go to the output.";    public static void runExample() {        System.out.println("Output example...");        TeeInputStream tee=null;        TeeInputStream teeIn = null;        TeeOutputStream teeOut = null;                try {            //TeeInputStream能將輸入資料流快速拷貝到輸出資料流中            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());                  //能將輸入資料流同時拷貝到兩個輸出資料流            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 {            //此處不需要關閉teeOut，當關閉teeIn時，同時會關閉teeOut            try { teeIn.close();            tee.close();}            catch (IOException e) { e.printStackTrace(); }        }    }

4、Filters，commons-io提供了多種過濾器，能夠根據條件過濾指定目錄下的檔案，同時還支援過濾器組合，

樣本如下

 private static final String PARENT_DIR =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio";    public static void runExample() {        System.out.println("File Filter example...");                        // NameFileFilter：擷取指定目錄下，符合給定檔案清單的檔案        //例如擷取此例，擷取PARENT_DIR目錄下commonios和commonio.txt檔案        File dir = FileUtils.getFile(PARENT_DIR);        String[] acceptedNames = {"commonios", "commonio.txt"};        for (String file: dir.list(new NameFileFilter(acceptedNames, IOCase.INSENSITIVE))) {            System.out.println("File found, named: " + file);        }                        //WildcardFileFilter：支援正則匹配，擷取指定目錄下，滿足正則的檔案        for (String file: dir.list(new WildcardFileFilter("*common*"))) {            System.out.println("Wildcard file found, named: " + file);        }                        // PrefixFileFilter：擷取以給定字串為首碼的檔案名稱        for (String file: dir.list(new PrefixFileFilter("common"))) {            System.out.println("Prefix file found, named: " + file);        }                        // SuffixFileFilter：：擷取以給定字串為尾碼的檔案名稱        for (String file: dir.list(new SuffixFileFilter(".txt"))) {            System.out.println("Suffix file found, named: " + file);        }                        // OrFileFilter：支援傳入多個過濾器，過濾器之間是或的關係        for (String file: dir.list(new OrFileFilter(                new WildcardFileFilter("*ample*"), new SuffixFileFilter(".txt")))) {            System.out.println("Or file found, named: " + file);        }                //AndFileFilter：支援傳入多個過濾器，過濾器之間是且的關係        for (String file: dir.list(new AndFileFilter(                 new WildcardFileFilter("*ample*"),                 new NotFileFilter(new SuffixFileFilter(".txt"))))) {             System.out.println("And/Not file found, named: " + file);        }    }

5、Comparators，commons-io提供了多種檔案比較工具類，能夠根據檔案名稱、檔案大小、修改時間等對目錄下的檔案進行排序，

簡單樣本如下

private static final String PARENT_DIR =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio";        private static final String FILE_1 =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio/commonio.txt";        private static final String FILE_2 =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio/test.xml";        public static void runExample() {        System.out.println("Comparator example...");                //NameFileComparator:根據檔案名稱排序，IOCase表示是否大小寫敏感                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：根據檔案大小排序，小檔案在前，其構造器支援傳一個boolean類型的參數，        //true表示需要計算該目錄下的目錄大小        //flase表示不需要計算該目錄下的目錄大小（0）                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：根據修改時間排序，最新修改排前        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);        }    }

6、File Monitor，commons-io還提供了對目錄的監控類，可以對指定目錄進行監控，如果目錄下檔案發生變化（修改，增加，刪除等），其監控會向監聽器發送相應的事件。

樣本如下

private static final String EXAMPLE_PATH =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio/commonio.txt";        private static final String PARENT_DIR =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio";        private static final String NEW_DIR =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio/newDir";        private static final String NEW_FILE =            "/Users/fly/work/GitHub/algorithm/src/main/java/com/fly/practice/apachecommonsio/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());                        // 檔案（目錄）監控                // 給指定目錄建立觀察者，並添加監聽器，對事件作出響應        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());                }        });                // 建立一個每隔500毫秒就做一次檢查的監控        FileAlterationMonitor monitor = new FileAlterationMonitor(500, observer);        try {            monitor.start();            //啟動監控後，對監控目錄做一些檔案操作，觸發監聽器            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();        }    }

以上只是對commons-io的一個簡單介紹，從中可以看出該工具包提供了強大的IO操作，更多功能還需實際項目中不斷探索

Apache Commons IO簡介