(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 subDirectories; public SubDirectoriesAndSize(final long totalSize, final List theSubDirs) { size = totalSize; subDirectories = Collections.unmodifiableList(theSubDirs); } } private SubDirectoriesAndSize getTotalAndSubDirs(final File file) { long total = 0; final List subDirectories = new ArrayList(); 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 directories = new ArrayList(); directories.add(file); while (!directories.isEmpty()) { final List> partialResults = new ArrayList>(); for (final File directory : directories) { partialResults.add(service .submit(new Callable() { public SubDirectoriesAndSize call() { return getTotalAndSubDirs(directory); } })); } directories.clear(); for (final Future 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> partialTotalFutures = new ArrayList>(); for (final File child : children) { partialTotalFutures.add(service.submit(new Callable() { public Long call() throws InterruptedException, ExecutionException, TimeoutException { return getTotalSizeOfFilesInDir(service, child); } })); } for (final Future 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 fileSizes = new ArrayBlockingQueue( 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 { 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> tasks = new ArrayList>(); for (final File child : children) { if (child.isFile()) { size += child.length(); } else { tasks.add(new FileSizeFinder(child)); } } for (final ForkJoinTask 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); } } 
