Java 多线程下载

测试类：

public class download_test {

    /**
     * @param args
     */
//    思路：
//
//            1、基本思路是将文件分段切割、分段传输、分段保存。
//
//            2、分段切割用到HttpUrlConnection对象的setRequestProperty("Range", "bytes=" + start + "-" + end)方法。
//
//            3、分段传输用到HttpUrlConnection对象的getInputStream()方法。
//
//            4、分段保存用到RandomAccessFile的seek(int start)方法。
//
//            5、创建指定长度的线程池，循环创建线程，执行下载操作。

    public static void main(String[] args) throws IOException {
        String urlLocation = "http://pic17.nipic.com/20111102/3707281_235344313129_2.jpg";
        String filename=DownloadFileWithThreadPool.getUrl_filename(urlLocation);
        String filePath="./"+filename;
        int poolLength=3;
        try {
            DownloadFileWithThreadPool manager = new DownloadFileWithThreadPool();
            manager.getFileWithThreadPool(urlLocation,filePath,poolLength);
            System.out.println("success");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

-

创建 线程池
执行：threadpool.execute(target)

public class DownloadFileWithThreadPool {
    public void getFileWithThreadPool(String urlLocation, String filePath, int poolLength) throws IOException {
        // Executor线程池
        Executor threadPool = Executors.newFixedThreadPool(poolLength);
        long len = getContentLength(urlLocation);
        for (int i = 0; i < poolLength; i++) {
            long start = i * len / poolLength;
            long end = (i + 1) * len / poolLength - 1;
            if (i == poolLength - 1) {
                end = len;
            }
            //DownloadWithRange实现runnable接口类，重写run函数
            DownloadWithRange download = new DownloadWithRange(urlLocation, filePath, start, end);
            threadPool.execute(download);   //Executor.execute(Runnalbe)
        }
    }

    public static long getContentLength(String urlLocation) throws IOException {
        URL url = null;
        if (urlLocation != null) {
            url = new URL(urlLocation);
        }
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setReadTimeout(5000);
        conn.setRequestMethod("GET");
        long len = conn.getContentLength();    //单位byte
     //   System.out.println("文件大小：" + len + " bytes");
        return len;
    }

    public static String getUrl_filename(String urlLocation) throws IOException {
        URL url = null;
        if (urlLocation != null) {
            url = new URL(urlLocation);
        }
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        URL absUrl = conn.getURL();// 获得真实Url
 //       System.out.println(absUrl.toString());
        // 打印输出服务器Header信息
//        Map<String, List<String>> map = conn.getHeaderFields();
//        for (String str : map.keySet()) {
//             System.out.println(str + "   " + map.get(str));
//        }
        String suffixes="avi|mpeg|3gp|mp3|mp4|wav|jpeg|gif|jpg|png|apk|exe|pdf|rar|zip|docx|doc";
        Pattern pat= Pattern.compile("[\\w]+[\\.]("+suffixes+")");
        Matcher mc=pat.matcher(absUrl.toString());
        String substring="";
        while(mc.find()){
            substring = mc.group();
            //System.out.println("filename:"+ substring);
        }
        return substring;
    }
}

执行分割文件以及保存类
1.分段切割用到HttpUrlConnection对象的setRequestProperty(“Range”, “bytes=” + start + “-” + end)
2.分段传输用到HttpUrlConnection对象的getInputStream()方法
将已经切割好的conn对象的数据下载下来
3.RandomAccessFile seek(start)方法将每一段数据保存下来

public class DownloadWithRange implements Runnable
{
    private String urlLocation;    //由url获取HttpURLConnection类型

    private String filePath;

    private long start;

    private long end;

    DownloadWithRange(String urlLocation, String filePath, long start, long end)
    {
        this.urlLocation = urlLocation;
        this.filePath = filePath;
        this.start = start;
        this.end = end;
    }

    @Override
    public void run()
    {
        try
        {
            HttpURLConnection conn = getHttp();
            conn.setRequestProperty("Range", "bytes=" + start + "-" + end);   //setRequestProperty函数进行文件切割

            File file = new File(filePath);
            RandomAccessFile out = null;
            if (file != null)
            {
                //对于待生成文件——file创建随机存取文件流
                out = new RandomAccessFile(file, "rwd");
            }
            out.seek(start);  //从start位置开始写入——seek函数
            InputStream in = conn.getInputStream();     //getInputStream分段传输。这里的HttpURLConnection已经是分割后的内容了
            byte[] b = new byte[1024];
            int len = 0;
            while ((len = in.read(b)) != -1)    //inputstream read 方法取出数据流中的数据  ————read()，read(byte[] b),read(byte[] b, int off, int len)
            {
                out.write(b, 0, len);    //把b内容写入out
            }
            in.close();
            out.close();
        }
        catch (Exception e)
        {
            e.getMessage();
        }

    }

    public HttpURLConnection getHttp() throws IOException
    {
        URL url = null;
        if (urlLocation != null)
        {
            url = new URL(urlLocation);
        }
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setReadTimeout(5000);
        conn.setRequestMethod("GET");
        return conn;
    }
}