Android实现网络多线程文件下载

实现原理

(1)首先获得下载文件的长度，然后设置本地文件的长度。

(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。

如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示：

（网上找的图）

 例如10M大小，使用3个线程来下载，

线程下载的数据长度   (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M
下载开始位置：线程id*每条线程下载的数据长度 = ?
下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

之前练习时的一个demo，不多说了，直接上代码吧，有关断点续传，需要使用数据库，不再加了，网上有很多成熟的项目可以直接用。

实例

MainApp：

package com.amos.app;

import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import com.amos.download.R;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

/**
 * @author yangxiaolong
 * @2014-5-6
 */
public class MainApp extends Activity implements OnClickListener {

    private static final String TAG = MainApp.class.getSimpleName();

    /** 显示下载进度TextView */
    private TextView mMessageView;
    /** 显示下载进度ProgressBar */
    private ProgressBar mProgressbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.progress_activity);
        findViewById(R.id.download_btn).setOnClickListener(this);
        mMessageView = (TextView) findViewById(R.id.download_message);
        mProgressbar = (ProgressBar) findViewById(R.id.download_progress);
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.download_btn) {
            doDownload();
        }
    }

    /**
     * 使用Handler更新UI界面信息
     */
    @SuppressLint("HandlerLeak")
    Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {

            mProgressbar.setProgress(msg.getData().getInt("size"));

            float temp = (float) mProgressbar.getProgress()
                    / (float) mProgressbar.getMax();

            int progress = (int) (temp * 100);
            if (progress == 100) {
                Toast.makeText(MainApp.this, "下载完成！", Toast.LENGTH_LONG).show();
            }
            mMessageView.setText("下载进度:" + progress + " %");

        }
    };

    /**
     * 下载准备工作，获取SD卡路径、开启线程
     */
    private void doDownload() {
        // 获取SD卡路径
        String path = Environment.getExternalStorageDirectory()
                + "/amosdownload/";
        File file = new File(path);
        // 如果SD卡目录不存在创建
        if (!file.exists()) {
            file.mkdir();
        }
        // 设置progressBar初始化
        mProgressbar.setProgress(0);

        // 简单起见，我先把URL和文件名称写死，其实这些都可以通过HttpHeader获取到
        String downloadUrl = "http://gdown.baidu.com/data/wisegame/91319a5a1dfae322/baidu_16785426.apk";
        String fileName = "baidu_16785426.apk";
        int threadNum = 5;
        String filepath = path + fileName;
        Log.d(TAG, "download file  path:" + filepath);
        downloadTask task = new downloadTask(downloadUrl, threadNum, filepath);
        task.start();
    }

    /**
     * 多线程文件下载
     * 
     * @author yangxiaolong
     * @2014-8-7
     */
    class downloadTask extends Thread {
        private String downloadUrl;// 下载链接地址
        private int threadNum;// 开启的线程数
        private String filePath;// 保存文件路径地址
        private int blockSize;// 每一个线程的下载量

        public downloadTask(String downloadUrl, int threadNum, String fileptah) {
            this.downloadUrl = downloadUrl;
            this.threadNum = threadNum;
            this.filePath = fileptah;
        }

        @Override
        public void run() {

            FileDownloadThread[] threads = new FileDownloadThread[threadNum];
            try {
                URL url = new URL(downloadUrl);
                Log.d(TAG, "download file http path:" + downloadUrl);
                URLConnection conn = url.openConnection();
                // 读取下载文件总大小
                int fileSize = conn.getContentLength();
                if (fileSize <= 0) {
                    System.out.println("读取文件失败");
                    return;
                }
                // 设置ProgressBar最大的长度为文件Size
                mProgressbar.setMax(fileSize);

                // 计算每条线程下载的数据长度
                blockSize = (fileSize % threadNum) == 0 ? fileSize / threadNum
                        : fileSize / threadNum + 1;

                Log.d(TAG, "fileSize:" + fileSize + "  blockSize:");

                File file = new File(filePath);
                for (int i = 0; i < threads.length; i++) {
                    // 启动线程，分别下载每个线程需要下载的部分
                    threads[i] = new FileDownloadThread(url, file, blockSize,
                            (i + 1));
                    threads[i].setName("Thread:" + i);
                    threads[i].start();
                }

                boolean isfinished = false;
                int downloadedAllSize = 0;
                while (!isfinished) {
                    isfinished = true;
                    // 当前所有线程下载总量
                    downloadedAllSize = 0;
                    for (int i = 0; i < threads.length; i++) {
                        downloadedAllSize += threads[i].getDownloadLength();
                        if (!threads[i].isCompleted()) {
                            isfinished = false;
                        }
                    }
                    // 通知handler去更新视图组件
                    Message msg = new Message();
                    msg.getData().putInt("size", downloadedAllSize);
                    mHandler.sendMessage(msg);
                    // Log.d(TAG, "current downloadSize:" + downloadedAllSize);
                    Thread.sleep(1000);// 休息1秒后再读取下载进度
                }
                Log.d(TAG, " all of downloadSize:" + downloadedAllSize);

            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    }

}

FileDownloadThread:

package com.amos.app;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.URL;
import java.net.URLConnection;
import android.util.Log;

/**
 * 文件下载类
 * 
 * @author yangxiaolong
 * @2014-5-6
 */
public class FileDownloadThread extends Thread {

    private static final String TAG = FileDownloadThread.class.getSimpleName();

    /** 当前下载是否完成 */
    private boolean isCompleted = false;
    /** 当前下载文件长度 */
    private int downloadLength = 0;
    /** 文件保存路径 */
    private File file;
    /** 文件下载路径 */
    private URL downloadUrl;
    /** 当前下载线程ID */
    private int threadId;
    /** 线程下载数据长度 */
    private int blockSize;

    /**
     * 
     * @param url:文件下载地址
     * @param file:文件保存路径
     * @param blocksize:下载数据长度
     * @param threadId:线程ID
     */
    public FileDownloadThread(URL downloadUrl, File file, int blocksize,
            int threadId) {
        this.downloadUrl = downloadUrl;
        this.file = file;
        this.threadId = threadId;
        this.blockSize = blocksize;
    }

    @Override
    public void run() {

        BufferedInputStream bis = null;
        RandomAccessFile raf = null;

        try {
            URLConnection conn = downloadUrl.openConnection();
            conn.setAllowUserInteraction(true);

            int startPos = blockSize * (threadId - 1);//开始位置
            int endPos = blockSize * threadId - 1;//结束位置
            //设置当前线程下载的起点、终点
            conn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);
            System.out.println(Thread.currentThread().getName() + "  bytes="
                    + startPos + "-" + endPos);

            byte[] buffer = new byte[1024];
            bis = new BufferedInputStream(conn.getInputStream());

            raf = new RandomAccessFile(file, "rwd");
            raf.seek(startPos);
            int len;
            while ((len = bis.read(buffer, 0, 1024)) != -1) {
                raf.write(buffer, 0, len);
                downloadLength += len;
            }
            isCompleted = true;
            Log.d(TAG, "current thread task has finished,all size:"
                    + downloadLength);

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (bis != null) {
                try {
                    bis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (raf != null) {
                try {
                    raf.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 线程文件是否下载完毕
     */
    public boolean isCompleted() {
        return isCompleted;
    }

    /**
     * 线程下载文件长度
     */
    public int getDownloadLength() {
        return downloadLength;
    }

}

效果图：