JAVA讀取文件夾年夜小的幾種辦法實例。本站提示廣大學習愛好者：（JAVA讀取文件夾年夜小的幾種辦法實例）文章只能為提供參考，不一定能成為您想要的結果。以下是JAVA讀取文件夾年夜小的幾種辦法實例正文
(一)單線程遞歸方法
package com.taobao.test;
import java.io.File;
public class TotalFileSizeSequential {
public static String fileName = "C:\\Documents and Settings\\Administrator\\桌面\\monkeytalk";
// 遞歸方法 盤算文件的年夜小
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）應用Executors.newFixedThreadPool和callable 多線程完成
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）應用Executors.newFixedThreadPool和callable 多線程的別的一種完成
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）應用CountDownLatch和AtomicLong完成多線程下的並發掌握
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）應用BlockingQueue和AtomicLong的完成
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)應用jdk7的ForkJoin來完成
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);
}
}
