本文主要包含多线程下载的一些简单demo,包括三部分

1. java实现
2. android实现
3. XUtils开源库实现

注意下载添加网络权限与SD卡读写权限

java实现多线程下载

public class MutileThreadDownload {

    /**

     * 线程的数量

     */

    private static int threadCount = 3;

    /**

     * 每个下载区块的大小

     */

    private static long blocksize;

    /**

     * 正在运行的线程的数量

     */

    private static int runningThreadCount;

    /**

     * @param args

     * @throws Exception

     */

    public static void main(String[] args) throws Exception {

        // 服务器文件的路径

        String path = "http://192.168.1.100:8080/ff.exe";

        URL url = new URL(path);

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

        conn.setRequestMethod("GET");

        conn.setConnectTimeout(5000);

        int code = conn.getResponseCode();

        if (code == 200) {

            long size = conn.getContentLength();// 得到服务端返回的文件的大小

            System.out.println("服务器文件的大小：" + size);

            blocksize = size / threadCount;

            // 1.首先在本地创建一个大小跟服务器一模一样的空白文件。

            File file = new File("temp.exe");

            RandomAccessFile raf = new RandomAccessFile(file, "rw");

            raf.setLength(size);

            // 2.开启若干个子线程分别去下载对应的资源。

            runningThreadCount = threadCount;

            for (int i = 1; i <= threadCount; i++) {

                long startIndex = (i - 1) * blocksize;

                long endIndex = i * blocksize - 1;

                if (i == threadCount) {

                    // 最后一个线程

                    endIndex = size - 1;

                }

                System.out.println("开启线程：" + i + "下载的位置：" + startIndex + "~"

                        + endIndex);

                new DownloadThread(path, i, startIndex, endIndex).start();

            }

        }

        conn.disconnect();

    }

    private static class DownloadThread extends Thread {

        private int threadId;

        private long startIndex;

        private long endIndex;

        private String path;

        public DownloadThread(String path, int threadId, long startIndex,

                long endIndex) {

            this.path = path;

            this.threadId = threadId;

            this.startIndex = startIndex;

            this.endIndex = endIndex;

        }

        @Override

        public void run() {

            try {

                // 当前线程下载的总大小

                int total = 0;

                File positionFile = new File(threadId + ".txt");

                URL url = new URL(path);

                HttpURLConnection conn = (HttpURLConnection) url

                        .openConnection();

                conn.setRequestMethod("GET");

                // 接着从上一次的位置继续下载数据

                if (positionFile.exists() && positionFile.length() > 0) {// 判断是否有记录

                    FileInputStream fis = new FileInputStream(positionFile);

                    BufferedReader br = new BufferedReader(

                            new InputStreamReader(fis));

                    // 获取当前线程上次下载的总大小是多少

                    String lasttotalstr = br.readLine();

                    int lastTotal = Integer.valueOf(lasttotalstr);

                    System.out.println("上次线程" + threadId + "下载的总大小："

                            + lastTotal);

                    startIndex += lastTotal;

                    total += lastTotal;// 加上上次下载的总大小。

                    fis.close();

                }

                conn.setRequestProperty("Range", "bytes=" + startIndex + "-"

                        + endIndex);

                conn.setConnectTimeout(5000);

                int code = conn.getResponseCode();

                System.out.println("code=" + code);

                InputStream is = conn.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：写文件的开始位置："

                        + String.valueOf(startIndex));

                int len = 0;

                byte[] buffer = new byte[512];

                while ((len = is.read(buffer)) != -1) {

                    RandomAccessFile rf = new RandomAccessFile(positionFile,

                            "rwd");

                    raf.write(buffer, 0, len);

                    total += len;

                    rf.write(String.valueOf(total).getBytes());

                    rf.close();

                }

                is.close();

                raf.close();

            } catch (Exception e) {

                e.printStackTrace();

            } finally {

                // 只有所有的线程都下载完毕后 才可以删除记录文件。

                synchronized (MutileThreadDownload.class) {

                    System.out.println("线程" + threadId + "下载完毕了");

                    runningThreadCount--;

                    if (runningThreadCount < 1) {

                        System.out.println("所有的线程都工作完毕了。删除临时记录的文件");

                        for (int i = 1; i <= threadCount; i++) {

                            File f = new File(i + ".txt");

                            System.out.println(f.delete());

                        }

                    }

                }

            }

        }

    }

}

安卓实现

public class MainActivity extends Activity {

    protected static final int DOWNLOAD_ERROR = 1;

    private static final int THREAD_ERROR = 2;

    public static final int DWONLOAD_FINISH = 3;

    private EditText et_path;

    private EditText et_count;

    /**

     * 存放进度条的布局

     */

    private LinearLayout ll_container;

    /**

     * 进度条的集合

     */

    private List<ProgressBar> pbs;

    /**

     * android下的消息处理器，在主线程创建，才可以更新ui

     */

    private Handler handler = new Handler(){

        public void handleMessage(Message msg) {

            switch (msg.what) {

            case DOWNLOAD_ERROR:

                Toast.makeText(getApplicationContext(), "下载失败", 0).show();

                break;

            case THREAD_ERROR:

                Toast.makeText(getApplicationContext(), "下载失败,请重试", 0).show();

                break;

            case DWONLOAD_FINISH:

                Toast.makeText(getApplicationContext(), "下载完成", 0).show();

                break;

            }

        };

    };

    /**

     * 线程的数量

     */

    private int threadCount = 3;

    /**

     * 每个下载区块的大小

     */

    private long blocksize;

    /**

     * 正在运行的线程的数量

     */

    private  int runningThreadCount;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        et_path = (EditText) findViewById(R.id.et_path);

        et_count = (EditText) findViewById(R.id.et_count);

        ll_container = (LinearLayout) findViewById(R.id.ll_container);

    }

    /**

     * 下载按钮的点击事件

     * @param view

     */

    public void downLoad(View view){

        //下载文件的路径

        final String path = et_path.getText().toString().trim();

        if(TextUtils.isEmpty(path)){

            Toast.makeText(this, "对不起下载路径不能为空", 0).show();

            return;

        }

        String count = et_count.getText().toString().trim();

        if(TextUtils.isEmpty(path)){

            Toast.makeText(this, "对不起,线程数量不能为空", 0).show();

            return;

        }

        threadCount = Integer.parseInt(count);

        //清空掉旧的进度条

        ll_container.removeAllViews();

        //在界面里面添加count个进度条

        pbs = new ArrayList<ProgressBar>();

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

            ProgressBar pb = (ProgressBar) View.inflate(this, R.layout.pb, null);

            ll_container.addView(pb);

            pbs.add(pb);

        }

        Toast.makeText(this, "开始下载", 0).show();

        new Thread(){

            public void run() {

                try {

                    URL url = new URL(path);

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

                    conn.setRequestMethod("GET");

                    conn.setConnectTimeout(5000);

                    int code = conn.getResponseCode();

                    if (code == 200) {

                        long size = conn.getContentLength();// 得到服务端返回的文件的大小

                        System.out.println("服务器文件的大小：" + size);

                        blocksize = size / threadCount;

                        // 1.首先在本地创建一个大小跟服务器一模一样的空白文件。

                        File file = new File(Environment.getExternalStorageDirectory(),getFileName(path));

                        RandomAccessFile raf = new RandomAccessFile(file, "rw");

                        raf.setLength(size);

                        // 2.开启若干个子线程分别去下载对应的资源。

                        runningThreadCount = threadCount;

                        for (int i = 1; i <= threadCount; i++) {

                            long startIndex = (i - 1) * blocksize;

                            long endIndex = i * blocksize - 1;

                            if (i == threadCount) {

                                // 最后一个线程

                                endIndex = size - 1;

                            }

                            System.out.println("开启线程：" + i + "下载的位置：" + startIndex + "~"

                                    + endIndex);

                            int threadSize = (int) (endIndex - startIndex);

                            pbs.get(i-1).setMax(threadSize);

                            new DownloadThread(path, i, startIndex, endIndex).start();

                        }

                    }

                    conn.disconnect();

                } catch (Exception e) {

                    e.printStackTrace();

                    Message msg = Message.obtain();

                    msg.what = DOWNLOAD_ERROR;

                    handler.sendMessage(msg);

                }

            };

        }.start();

    }

    private class DownloadThread extends Thread {

        private int threadId;

        private long startIndex;

        private long endIndex;

        private String path;

        public DownloadThread(String path, int threadId, long startIndex,

                long endIndex) {

            this.path = path;

            this.threadId = threadId;

            this.startIndex = startIndex;

            this.endIndex = endIndex;

        }

        @Override

        public void run() {

            try {

                // 当前线程下载的总大小

                int total = 0;

                File positionFile = new File(Environment.getExternalStorageDirectory(),getFileName(path)+threadId + ".txt");

                URL url = new URL(path);

                HttpURLConnection conn = (HttpURLConnection) url

                        .openConnection();

                conn.setRequestMethod("GET");

                // 接着从上一次的位置继续下载数据

                if (positionFile.exists() && positionFile.length() > 0) {// 判断是否有记录

                    FileInputStream fis = new FileInputStream(positionFile);

                    BufferedReader br = new BufferedReader(

                            new InputStreamReader(fis));

                    // 获取当前线程上次下载的总大小是多少

                    String lasttotalstr = br.readLine();

                    int lastTotal = Integer.valueOf(lasttotalstr);

                    System.out.println("上次线程" + threadId + "下载的总大小："

                            + lastTotal);

                    startIndex += lastTotal;

                    total += lastTotal;// 加上上次下载的总大小。

                    fis.close();

                    //存数据库。

                    //_id path threadid total

                }

                conn.setRequestProperty("Range", "bytes=" + startIndex + "-"

                        + endIndex);

                conn.setConnectTimeout(5000);

                int code = conn.getResponseCode();

                System.out.println("code=" + code);

                InputStream is = conn.getInputStream();

                File file = new File(Environment.getExternalStorageDirectory(),getFileName(path));

                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：写文件的开始位置："

                        + String.valueOf(startIndex));

                int len = 0;

                byte[] buffer = new byte[1024];

                while ((len = is.read(buffer)) != -1) {

                    RandomAccessFile rf = new RandomAccessFile(positionFile,

                            "rwd");

                    raf.write(buffer, 0, len);

                    total += len;

                    rf.write(String.valueOf(total).getBytes());

                    rf.close();

                    pbs.get(threadId-1).setProgress(total);

                }

                is.close();

                raf.close();

            } catch (Exception e) {

                e.printStackTrace();

                Message msg = Message.obtain();

                msg.what = THREAD_ERROR;

                handler.sendMessage(msg);

            } finally {

                // 只有所有的线程都下载完毕后 才可以删除记录文件。

                synchronized (MainActivity.class) {

                    System.out.println("线程" + threadId + "下载完毕了");

                    runningThreadCount--;

                    if (runningThreadCount < 1) {

                        System.out.println("所有的线程都工作完毕了。删除临时记录的文件");

                        for (int i = 1; i <= threadCount; i++) {

                            File f = new File(Environment.getExternalStorageDirectory(),getFileName(path)+ i + ".txt");

                            System.out.println(f.delete());

                        }

                        Message msg = Message.obtain();

                        msg.what = DWONLOAD_FINISH;

                        handler.sendMessage(msg);

                    }

                }

            }

        }

    }

    //http://192.168.1.100:8080/aa.exe

    private String getFileName(String path){

        int start = path.lastIndexOf("/")+1;

        return path.substring(start);

    }

}

利用XUtils开源框架实现，需要XUtils的jar包

public class MainActivity extends Activity {

    private EditText et_path;

    private TextView tv_info;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        et_path = (EditText) findViewById(R.id.et_path);

        tv_info = (TextView) findViewById(R.id.tv_info);

    }

    public void download(View view){

        String path = et_path.getText().toString().trim();

        if(TextUtils.isEmpty(path)){

            Toast.makeText(this, "请输入下载的路径", 0).show();

            return;

        }else{

            HttpUtils http = new HttpUtils();

            HttpHandler handler = http.download(path,

                    "/sdcard/xxx.zip",

                    true, // 如果目标文件存在，接着未完成的部分继续下载。服务器不支持RANGE时将从新下载。

                    true, // 如果从请求返回信息中获取到文件名，下载完成后自动重命名。

                    new RequestCallBack<File>() {

                        @Override

                        public void onStart() {

                            tv_info.setText("conn...");

                        }

                        @Override

                        public void onLoading(long total, long current, boolean isUploading) {

                            tv_info.setText(current + "/" + total);

                        }

                        @Override

                        public void onSuccess(ResponseInfo<File> responseInfo) {

                            tv_info.setText("downloaded:" + responseInfo.result.getPath());

                        }

                        @Override

                        public void onFailure(HttpException error, String msg) {

                            tv_info.setText(msg);

                        }

                });

        }

    }

}

完成