发布于 2016-07-19 19:45:41 | 43 次阅读 | 评论: 0 | 来源: 网友投递

这里有新鲜出炉的Java函数式编程,程序狗速度看过来!

Java程序设计语言

java 是一种可以撰写跨平台应用软件的面向对象的程序设计语言,是由Sun Microsystems公司于1995年5月推出的Java程序设计语言和Java平台(即JavaEE(j2ee), JavaME(j2me), JavaSE(j2se))的总称。


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);
    }
}



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