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这篇文章介绍了JAVA读取文件夹大小的几种方法实例，有需要的朋友可以参考一下

(一)单线程递归方式

package com.taobao.test; 
import java.io.File; 

public class TotalFileSizeSequential {     
    public static String fileName = "C:\\Documents and Settings\\Administrator\\桌面\\monkeytalk";     
    // 递归方式 计算文件的大小     
    private long getTotalSizeOfFilesInDir(final File file) {         
        if (file.isFile())             
            return file.length();         
        final File[] children = file.listFiles();         
        long total = 0;         
        if (children != null)             
            for (final File child : children)                 
                total += getTotalSizeOfFilesInDir(child);         
        return total;     
        }     
    public static void main(final String[] args) {         
        final long start = System.nanoTime();         
        final long total = new TotalFileSizeSequential().getTotalSizeOfFilesInDir(new File(fileName));         
        final long end = System.nanoTime();         
        System.out.println("Total Size: " + total);         
        System.out.println("Time taken: " + (end - start) / 1.0e9);     
        } 
 }

(二)使用Executors.newFixedThreadPool和callable 多线程实现

package com.taobao.test; 
import java.io.File; 
import java.util.ArrayList; 
import java.util.Collections; 
import java.util.List; 
import java.util.concurrent.Callable; 
import java.util.concurrent.ExecutionException; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.Future; 
import java.util.concurrent.TimeUnit; 
import java.util.concurrent.TimeoutException; 
public class ConcurrentTotalFileSize {     
    public static final String fileName = "C:\\Documents and Settings\\Administrator\\桌面\\monkeytalk";     
    class SubDirectoriesAndSize {         
        final public long size;         
        final public List<File> subDirectories;         
        public SubDirectoriesAndSize(final long totalSize,                 
        final List<File> theSubDirs) {             
            size = totalSize;             
            subDirectories = Collections.unmodifiableList(theSubDirs);         
        }     
    }     
    private SubDirectoriesAndSize getTotalAndSubDirs(final File file) {         
        long total = 0;         
        final List<File> subDirectories = new ArrayList<File>();         
        if (file.isDirectory()) {             
            final File[] children = file.listFiles();             
            if (children != null)                 
            for (final File child : children) {                     
                if (child.isFile())                         
                    total += child.length();                     
                else                         
                subDirectories.add(child);                 
            }         
        }         
        return new SubDirectoriesAndSize(total, subDirectories);     
    }     
    private long getTotalSizeOfFilesInDir(final File file)             
    throws InterruptedException, ExecutionException, TimeoutException {         
        final ExecutorService service = Executors.newFixedThreadPool(100);         
        try {             
            long total = 0;             
            final List<File> directories = new ArrayList<File>();             
            directories.add(file);             
            while (!directories.isEmpty()) {                 
                final List<Future<SubDirectoriesAndSize>> partialResults = new ArrayList<Future<SubDirectoriesAndSize>>();                 
                for (final File directory : directories) {                     
                    partialResults.add(service.submit(new Callable<SubDirectoriesAndSize>() {                                 
                        public SubDirectoriesAndSize call() {                                     
                            return getTotalAndSubDirs(directory);                                 
                        }                             
                    }));                 
                }                 
                directories.clear();                 
                for (final Future<SubDirectoriesAndSize> partialResultFuture : partialResults) {                     
                    final SubDirectoriesAndSize subDirectoriesAndSize = partialResultFuture.get(100, TimeUnit.SECONDS);                     
                    directories.addAll(subDirectoriesAndSize.subDirectories);                     
                    total += subDirectoriesAndSize.size;                 
                }             
            }             
            return total;         
        } finally {             
            service.shutdown();         
           }     
       }    
       public static void main(final String[] args) throws InterruptedException,             
       ExecutionException, TimeoutException {         
           final long start = System.nanoTime();         
           final long total = new ConcurrentTotalFileSize().getTotalSizeOfFilesInDir(new File(fileName));         
           final long end = System.nanoTime();         
           System.out.println("Total Size: " + total);         
           System.out.println("Time taken: " + (end - start) / 1.0e9);     
       } 
   }

(三)使用Executors.newFixedThreadPool和callable 多线程的另外一种实现

package com.taobao.test;  
import java.io.File; 
import java.util.ArrayList; 
import java.util.List; 
import java.util.concurrent.Callable; 
import java.util.concurrent.ExecutionException; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.Future; 
import java.util.concurrent.TimeUnit; 
import java.util.concurrent.TimeoutException; 
public class NaivelyConcurrentTotalFileSize {     
    public static String fileName = "C:\\Documents and Settings\\Administrator\\桌面\\monkeytalk";     
    private long getTotalSizeOfFilesInDir(final ExecutorService service, final File file) 
    throws InterruptedException, ExecutionException, TimeoutException {         
        if (file.isFile())             
            return file.length();         
        long total = 0;         
        final File[] children = file.listFiles();         
        if (children != null) {             
            final List<Future<Long>> partialTotalFutures = new ArrayList<Future<Long>>();             
            for (final File child : children) {                 
                partialTotalFutures.add(service.submit(new Callable<Long>() {                     
                    public Long call() throws InterruptedException,                             
                    ExecutionException, TimeoutException {                         
                    return getTotalSizeOfFilesInDir(service, child);                     
                    }                 
                }));             
            }             
            for (final Future<Long> partialTotalFuture : partialTotalFutures)                 
            total += partialTotalFuture.get(100, TimeUnit.SECONDS);         
        }         
        return total;    
    }     
    private long getTotalSizeOfFile(final String fileName)             
    throws InterruptedException, ExecutionException, TimeoutException {         
        final ExecutorService service = Executors.newFixedThreadPool(100);         
        try {             
            return getTotalSizeOfFilesInDir(service, new File(fileName));         
        } finally {             
            service.shutdown();         
            }     
    }     
    public static void main(final String[] args) throws InterruptedException,ExecutionException, TimeoutException {         
        final long start = System.nanoTime();         
        final long total = new NaivelyConcurrentTotalFileSize().getTotalSizeOfFile(fileName);         
        final long end = System.nanoTime();         
        System.out.println("Total Size: " + total);         
        System.out.println("Time taken: " + (end - start) / 1.0e9);     
    } 
}

(四)使用CountDownLatch和AtomicLong实现多线程下的并发控制

package com.taobao.test; 
import java.io.File; 
import java.util.concurrent.CountDownLatch; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.TimeUnit; 
import java.util.concurrent.atomic.AtomicLong; 
public class ConcurrentTotalFileSizeWLatch {    
     private ExecutorService service;     
     final private AtomicLong pendingFileVisits = new AtomicLong();     
     final private AtomicLong totalSize = new AtomicLong();     
     final private CountDownLatch latch = new CountDownLatch(1);     
     public static String fileName = "C:\\Documents and Settings\\Administrator\\桌面\\monkeytalk";     
     private void updateTotalSizeOfFilesInDir(final File file) {         
         long fileSize = 0;         
         if (file.isFile())             
         fileSize = file.length();         
         else {             
             final File[] children = file.listFiles();             
             if (children != null) {                 
                 for (final File child : children) {                     
                 if (child.isFile())                         
                     fileSize += child.length();                     
                 else {                         
                     pendingFileVisits.incrementAndGet();                         
                     service.execute(new Runnable() {                             
                         public void run() {                                 
                         updateTotalSizeOfFilesInDir(child);                             
                         }                         
                     });                     
                 }                 
             }             
         }         
     }         
     totalSize.addAndGet(fileSize);         
     if (pendingFileVisits.decrementAndGet() == 0)             
         latch.countDown();     
     }     
     private long getTotalSizeOfFile(final String fileName)             
     throws InterruptedException {         
         service = Executors.newFixedThreadPool(100);         
         pendingFileVisits.incrementAndGet();         
         try {             
             updateTotalSizeOfFilesInDir(new File(fileName));             
             latch.await(100, TimeUnit.SECONDS);             
             return totalSize.longValue();         
         } finally {             
                 service.shutdown();         
             }     
     }     
     public static void main(final String[] args) throws InterruptedException {         
         final long start = System.nanoTime();         
         final long total = new ConcurrentTotalFileSizeWLatch().getTotalSizeOfFile(fileName);         
         final long end = System.nanoTime();         
         System.out.println("Total Size: " + total);         
         System.out.println("Time taken: " + (end - start) / 1.0e9);     
     } 
 }

(五)使用BlockingQueue和AtomicLong的实现

package com.taobao.test; 
import java.io.File; 
import java.util.concurrent.ArrayBlockingQueue; 
import java.util.concurrent.BlockingQueue; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.TimeUnit; 
import java.util.concurrent.atomic.AtomicLong; 
public class ConcurrentTotalFileSizeWQueue {     
    public static String fileName = "C:\\Documents and Settings\\Administrator\\桌面\\monkeytalk";      
    private ExecutorService service;     
    final private BlockingQueue<Long> fileSizes = new ArrayBlockingQueue<Long>(500);     
    final AtomicLong pendingFileVisits = new AtomicLong();     
    private void startExploreDir(final File file) {         
        pendingFileVisits.incrementAndGet();         
        service.execute(new Runnable() {             
            public void run() {                 
                exploreDir(file);             
            }         
        });     
    }     
    private void exploreDir(final File file) {         
        long fileSize = 0;         
        if (file.isFile())             
        fileSize = file.length();         
        else {             
            final File[] children = file.listFiles();             
            if (children != null)                 
            for (final File child : children) {                     
                if (child.isFile())                         
                fileSize += child.length();                     
                else {                         
                    startExploreDir(child);                     
                }                 
            }         
        }         
        try {             
            fileSizes.put(fileSize);         
        } catch (Exception ex) {             
            throw new RuntimeException(ex);         
        }         
        pendingFileVisits.decrementAndGet();     
    }     
    private long getTotalSizeOfFile(final String fileName)             
    throws InterruptedException {         
        service = Executors.newFixedThreadPool(100);         
        try {             
            startExploreDir(new File(fileName));             
            long totalSize = 0;             
            while (pendingFileVisits.get() > 0 || fileSizes.size() > 0) {                 
                final Long size = fileSizes.poll(10, TimeUnit.SECONDS);                 
                totalSize += size;             
            }             
            return totalSize;         
        } finally {             
            service.shutdown();         
        }     
    }     
    public static void main(final String[] args) throws InterruptedException {         
        final long start = System.nanoTime();         
        final long total = new ConcurrentTotalFileSizeWQueue().getTotalSizeOfFile(fileName);         
        final long end = System.nanoTime();         
        System.out.println("Total Size: " + total);         
        System.out.println("Time taken: " + (end - start) / 1.0e9);     
    } 
}

(六)使用jdk7的ForkJoin来实现

package com.taobao.test; import java.io.File; import java.util.ArrayList; import java.util.List; import java.util.concurrent.ForkJoinPool; import java.util.concurrent.ForkJoinTask; import java.util.concurrent.RecursiveTask; public class FileSize {     private final static ForkJoinPool forkJoinPool = new ForkJoinPool();     public static String fileName = "C:\\Documents and Settings\\Administrator\\桌面\\monkeytalk";      private static class FileSizeFinder extends RecursiveTask<Long> {         final File file;         public FileSizeFinder(final File theFile) {             file = theFile;         }         @Override         public Long compute() {             long size = 0;             if (file.isFile()) {                 size = file.length();             } else {                 final File[] children = file.listFiles();                 if (children != null) {                     List<ForkJoinTask<Long>> tasks = new ArrayList<ForkJoinTask<Long>>();                     for (final File child : children) {                         if (child.isFile()) {                             size += child.length();                         } else {                             tasks.add(new FileSizeFinder(child));                         }                     }                     for (final ForkJoinTask<Long> task : invokeAll(tasks)) {                         size += task.join();                     }                 }             }             return size;         }     }     public static void main(final String[] args) {         final long start = System.nanoTime();         final long total = forkJoinPool.invoke(new FileSizeFinder(new File("/home")));         final long end = System.nanoTime();         System.out.println("Total Size: " + total);         System.out.println("Time taken: " + (end - start) / 1.0e9);     } } 

原文：51CTO.COM