Android菜鸟之路-多线程下载

Android客户端下载步骤

在Android客户端首先创建一个空文件（空白文件），大小跟服务器的一模一样。
开启若干线程，分别去下载服务器上对应的资源。
如果所有的线程都下载完毕，服务器的资源就下载完毕。

Android客户端下载逻辑

获取到服务器端资源文件的大小(connection.getContentLength())

String path = "http://localhost:8080/ff.exe";URL url = new URL(path);// 获取链接HttpURLConnection connection = (HttpURLConnection) url.openConnection();// 参数connection.setRequestMethod("GET");connection.setConnectTimeout(5000);// 响应码int responseCode = connection.getResponseCode();if (responseCode == 200) {    // 得到服务端返回的文件大小    long contentLength = connection.getContentLength();    System.out.println("服务器文件大小:"+contentLength);}// 断开连接connection.disconnect();

在本地创建一个大小和服务器一样的的空白文件

File file = new File("temp.ext");RandomAccessFile raf= new RandomAccessFile(file, "rw");raf.setLength(contentLength);

根据开启线程的数量，把服务器资源给等分成若干份（threadCount：线程数量）

假设文件大小是10个byte。（长度：length）假设3个线程（线程数量：threadCount）。 int blockSize = length / threadCount;线程1 下载3个byte    1-3     0 * blockSize + 1 ~ 1 * blockSize线程2 下载3个byte    4-6     1 * blockSize + 1 ~ 2 * blockSize 线程3 下载4个byte    7-10    2 * blockSize + 1 ~ 3 * blockSize(length)// 开启若干个子线程，分别去下载对应的资源long threadCount = 3;long blockSize = contentLength / threadCount;for (int i = 1; i <= threadCount; i++) {    // 计算下载起始、结束位置    long startIndex = (i - 1) * blockSize + 0;// 服务器也是从0开始    long endIndex = i * blockSize - 1; //    // 最后一个线程    if (i == threadCount) {        endIndex = contentLength - 1;    }    System.out.println("开启线程:" + i + "，下载的位置：(" + startIndex + "~"            + endIndex + ")");    new DownloadThread(i, startIndex, endIndex, path).start();}

创建线程类

static class DownloadThread extends Thread {    private int threadId;    private long startIndex;    private long endIndex;    private String path;    public DownloadThread(int threadId, long startIndex, long endIndex,            String path) {        super();        this.threadId = threadId;        this.startIndex = startIndex;        this.endIndex = endIndex;        this.path = path;    }    public void run() {        URL url;        try {            url = new URL(path);            // 获取链接            HttpURLConnection connection = (HttpURLConnection) url                    .openConnection();            // 参数            connection.setRequestMethod("GET");            connection.setConnectTimeout(5000);            // 告诉服务器下载的参数            connection.setRequestProperty("Range", "bytes=" + startIndex                    + "-" + endIndex);            // 响应码            int responseCode = connection.getResponseCode();            System.out.println("服务器状态码:" + responseCode);            // 下载服务器文件，返回的是206            if (responseCode == 206) {                InputStream inputStream = connection.getInputStream();                File file = new File("temp.exe");                RandomAccessFile raf = new RandomAccessFile(file, "rw");                // 指定文件开始写的位置                raf.seek(startIndex);                System.out.println("第" + threadId + "个线程，写文件的开始、结束位置("                        + (startIndex) + "," + (endIndex) + ")");                int len = 0;                 byte[] buf = new byte[1024];                while ((len = inputStream.read(buf)) != -1) {                    raf.write(buf, 0, len);                }                inputStream.close();                raf.close();                System.out.println("第" + threadId + "个线程下载完毕了");            }        } catch (Exception e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}

Android客户端下载步骤

Android客户端下载逻辑

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