Java多线程文件下载

来源：互联网发布：什么是大数据云计算编辑：程序博客网时间：2024/05/16 06:01

一. 多线程下载文件考虑处理步骤：

1. 如何获取文件的长度

2. 合理的创建线程数量，并计算每一个线程下载的长度

3. 如何将多个线程下载的字节写入到文件中

二. 代码实现如下：

package com.bochao.download;import java.io.File;import java.net.URL;import java.net.URLConnection;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * HTTP多线程下载 *  * @Author DuanCZ * @Date 2015年9月30日-上午9:28:28 */public class HttpMulitThreadDownload {// 下载文件路径private String downloadFilePath = null;// 保存文件路径private String saveFileDir = "c:\\";// 默认合理并发线程数private int threadCount = Runtime.getRuntime().availableProcessors() * 2;// 新文件名称private String newFileName = null;public HttpMulitThreadDownload(int threadCount, String downloadFilePath, String saveFileDir, String newFileName) {// 用户指定线程数如果小于默认线程数则使用用户指定线程数if (threadCount < this.threadCount) {this.threadCount = threadCount;}this.downloadFilePath = downloadFilePath;this.saveFileDir = saveFileDir;this.newFileName = newFileName;}public void MulitThreadDownload() {// 数据合法性验证if (null == downloadFilePath || downloadFilePath.isEmpty()) {throw new RuntimeException("请指定下载路径!");}if (null == saveFileDir || saveFileDir.isEmpty()) {throw new RuntimeException("请指定保存路径!");}// 创建保存文件路径如果不存在File saveFileDirTemp = new File(saveFileDir);if (!saveFileDirTemp.exists()) {saveFileDirTemp.mkdirs();}// 处理文件名称if (null == newFileName || newFileName.isEmpty()) {newFileName = downloadFilePath.substring(downloadFilePath.lastIndexOf("/") + 1, downloadFilePath.length());}// 创建固定大小的线程池ExecutorService threadPool = Executors.newFixedThreadPool(threadCount);try {// 根据文件长度计算合理线程数开始URLConnection urlConnection = new URL(downloadFilePath).openConnection();// 获取文件长度int downloadFileLength = urlConnection.getContentLength();// 计算每个线程负责的文件字节长度int averageThreadLength = downloadFileLength / threadCount;int residueThreadLength = downloadFileLength % threadCount;// 让每一个线程开始工作int startIndex = 0;int endIndex = 0;for (int i = 0; i < threadCount; i++) {// 计算每一个线程开始和计数索引startIndex = i * averageThreadLength;// 如果是最后一个线程，则将剩余的全部下载if ((i + 1) == threadCount) {endIndex = (i + 1) * averageThreadLength + residueThreadLength - 1;}endIndex = (i + 1) * averageThreadLength - 1;// 创建下载线程对象DownloadHandlerThread downloadHandlerThread = new DownloadHandlerThread();downloadHandlerThread.setDownloadFilePath(downloadFilePath);downloadHandlerThread.setSaveFilePath(saveFileDir + newFileName);downloadHandlerThread.setStartIndex(startIndex);downloadHandlerThread.setEndIndex(endIndex);threadPool.execute(downloadHandlerThread);}} catch (Exception e) {e.printStackTrace();} finally {// 关闭线程池threadPool.shutdown();}}}

package com.bochao.download;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.URL;import java.net.URLConnection;import java.text.SimpleDateFormat;import java.util.Date;/** * 下载文件处理线程 *  * @Author DuanCZ * @Date 2015年9月30日-上午11:38:42 */public class DownloadHandlerThread implements Runnable {    // 待下载的HTTP文件路径    private String downloadFilePath = null;    // 下载保存文件路径    private String saveFilePath = null;    // 文件随机写入开始索引    private int startIndex = 0;    // 文件随机写入结束索引    private int endIndex = 0;    @Override    public void run() {        System.out.println("线程名称[" + Thread.currentThread().getName() + "]于时间["                + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "]开始下载....");        // 文件输入流对象        InputStream fileInputStream = null;        // 随机访问文件        RandomAccessFile randomAccessFile = null;        // ------------------------------------------------------------------------------        // 获取随机文件流开始        // 获取一个URL打开链接对象        URLConnection urlConnection = null;        try {            urlConnection = new URL(downloadFilePath).openConnection();        } catch (IOException e1) {            e1.printStackTrace();        }        // 设置该链接允许和用户交互        urlConnection.setAllowUserInteraction(true);        // 设置请求属性字节范围        urlConnection.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex + "");        try {            // 获取指定的文件流            fileInputStream = urlConnection.getInputStream();        } catch (IOException e) {            e.printStackTrace();        }        // ------------------------------------------------------------------------------获取随机文件流结束        // ------------------------------------------------------------------------        // 写文件流到指定的文件开始        try {            // 创建文件随机访问对象            randomAccessFile = new RandomAccessFile(saveFilePath, "rw");            // 将文件写入位置移动到其实点            randomAccessFile.seek(startIndex);            // 写入文件            int bytes = 0;            byte[] buffer = new byte[100 * 1024];            while ((bytes = fileInputStream.read(buffer, 0, buffer.length)) != -1) {                randomAccessFile.write(buffer, 0, bytes);            }        } catch (IOException e) {            e.printStackTrace();        } finally {            try {                if (null != randomAccessFile) {                    randomAccessFile.close();                }                if (null != fileInputStream) {                    fileInputStream.close();                }            } catch (IOException e) {                e.printStackTrace();            }        }        // ------------------------------------------------------------------------写文件流到指定的文件结束        System.out.println("线程名称[" + Thread.currentThread().getName() + "]于时间["                + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "]下载完成！");    }    public String getDownloadFilePath() {        return downloadFilePath;    }    public void setDownloadFilePath(String downloadFilePath) {        this.downloadFilePath = downloadFilePath;    }    public String getSaveFilePath() {        return saveFilePath;    }    public void setSaveFilePath(String saveFilePath) {        this.saveFilePath = saveFilePath;    }    public int getStartIndex() {        return startIndex;    }    public void setStartIndex(int startIndex) {        this.startIndex = startIndex;    }    public int getEndIndex() {        return endIndex;    }    public void setEndIndex(int endIndex) {        this.endIndex = endIndex;    }}

测试：

package com.bochao.download;public class TestDownload {public static void main(String[] args) {    String downloadFilePath = "http://localhost:81/mulitThreadDownload/file/PowerDesigner165_Evaluation.1428562995.exe";String saveFileDir= "f:\\Download\\";HttpMulitThreadDownload httpMulitThreadDownload = new HttpMulitThreadDownload(2, downloadFilePath, saveFileDir, "powerdesigner.exe");httpMulitThreadDownload.MulitThreadDownload();}}

输出结果：

线程名称[pool-1-thread-1]于时间[2015-08-30 16:09:49]开始下载....
线程名称[pool-1-thread-2]于时间[2015-08-30 16:09:49]开始下载....
线程名称[pool-1-thread-2]于时间[2015-09-30 16:09:01]下载完成！
线程名称[pool-1-thread-1]于时间[2015-09-30 16:09:23]下载完成！

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