javascript批量下载文件

平时开发中有时会用到文件下载,为了提高文件的下载速率,采用多线程下载能够达到事半功倍的效果:

package test;

/**

 * 文件下载类

 * @author luweicheng

 *

 */

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

import java.net.URLConnection;

 

public class DownFile {

    private URL fileUrl;// 文件下载路径

    private int threadCount;// 文件下载的线程数

    private int startPos;// 每个线程下载文件的开始位置

    private int size;// 每个线程下载文件的长度

    private int fileLength;// 文件总程度

    private String pathName;// 下载的文件路径(包含文件名)

    private Downthread[] tDownthreads;// 线程数组

 

    public DownFile(URL url, int threadCount, String pathName) throws IOException {

        fileUrl = url;

        this.threadCount = threadCount;

        this.pathName = pathName;

        init();

 

    }

 

    /**

     * 初始化

     *

     * @throws IOException

     */

    private void init() throws IOException {

        tDownthreads = new Downthread[threadCount];

        HttpURLConnection conn = (HttpURLConnection) fileUrl.openConnection();

        conn.setConnectTimeout(5000);

        conn.setRequestMethod(“GET”);

        conn.setRequestProperty(“connection”, “keep-alive”);

        fileLength = conn.getContentLength();

        System.out.println(“文件长度” + fileLength);

        size = fileLength / threadCount;

        System.out.println(“每个下载量==” + size);

        conn.disconnect();// 断开链接

 

    }

 

    public URL getFileUrl() {

        return fileUrl;

    }

 

    public int getThreadCount() {

        return this.threadCount;

    }

 

    /**

     * 开始下载

     */

    public void startDown() {

        for (int i = 0; i < threadCount; i++) {

            try {

                RandomAccessFile raFile = new RandomAccessFile(pathName, “rw”);

                tDownthreads[i] = new Downthread(i * size, raFile, i);

                tDownthreads[i].start();

            } catch (FileNotFoundException e) {

                e.printStackTrace();

            }

 

        }

 

    }

 

    /**

     * 下载线程类

     *

     * @author luweicheng

     *

     */

    class Downthread extends Thread {

        private int startPos;// 开始的位置

        private InputStream is;

        private RandomAccessFile raFile;

        private int length;// 下载的文件长度

        private int flag;// 线程标志

 

        public Downthread(int startPos, RandomAccessFile raFile, int i) {

            this.startPos = startPos;

            this.raFile = raFile;

            flag = i;

        }

 

        @Override

        public void run() {

            try {

                HttpURLConnection connection = (HttpURLConnection) fileUrl.openConnection();

                connection.setRequestMethod(“GET”);

                connection.setRequestProperty(“connection”, “keep-alive”);

                connection.setConnectTimeout(5 * 1000);

                is = connection.getInputStream();

                is.skip(startPos);

                raFile.seek(startPos);

                byte[] buf = new byte[8 * 1024];

                int hasread = 0;// 读出的字节数

                // 将位置在 startPos – startPos 位置的数据读出写入

                while (length < size && (hasread = is.read(buf)) != -1) {

                    raFile.write(buf, 0, hasread);

                    length += hasread;

                    System.out.println(“*****线程” + flag + “下载了*********” + length);

                }

                System.out.println(“*******线程” + flag + “下载完成*********”);

            } catch (IOException e) {

            } finally {

                try {

                    is.close();

                    raFile.close();

                } catch (IOException e) {

                    e.printStackTrace();

                }

            }

        }

    }

}

 

效果展示:

 

详细配置信息可以参考这篇文章:

http://blog.ncmem.com/wordpress/2019/08/28/java%e6%89%b9%e9%87%8f%e4%b8%8b%e8%bd%bd/