Android多线程下载

一、多线程下载的原理、

      

      将服务端的资源划分给成几个等分的块，分配给不同的线程同时执行下载。

      划分方法 ：

                  每个线程分配的长度为：int blocksize = length/n    

                  每个线程的起止位置（i-1）*blocksize--->i*blocksize-1        

                  最后一个线程结束位置为length

二、步骤：

       1、在客户端创建与服务端同等大小的文件，使用RandomAccessFile类远程文件的设置操作

       2.、开启几个线程，分配下载资源

       3.、所有的线程执行完毕之后，文件下载完毕

三、java实现的多线程下载

package com.lewu.download;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class DownloadTest {
    public static final String path = "http://192.168.1.118:8080/web/youdao.exe";
    public static int threadcount = 0;

    public static void main(String[] args) throws Exception {
        // 1.在客户端端创建一个相同大小的文件（获取服务器文件的大小）

        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5000);
        conn.setRequestProperty(
                "User-Agent",
                "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
        int length = conn.getContentLength();
        System.err.println("文件的长度为"+length);
        File file = new File("youdao.exe");
        RandomAccessFile randomfile = new RandomAccessFile(file, "rwd");
        randomfile.setLength(length);

        // 创建三个线程 :线程分配下载资源
        int blocksize = length / 3;
        for (int i = 1; i <=3; i++) {
            // 线程执行下载操作 ，需要定位下载的位置，则需要设置一些参数
            int beginsize = (i - 1) * blocksize;
            int endsize = i * blocksize - 1;
            if (i == 3) {
                endsize = length;
            }
            int id = i;

            // 启动线程
            new Thread(new DownloadThread(id, beginsize, endsize)).start();
        }

    }

    static class DownloadThread implements Runnable {

        private int id;
        private int beginsize;
        private int endsize;

        public DownloadThread(int id, int beginsize, int endsize) {
            this.id = id;
            this.beginsize = beginsize;
            this.endsize = endsize;
        }

        @Override
        public void run() {
            try {
                // 每一个线程在创建的时候 都创建一个名为id.text的文件用来保存下载进度
                File idfile = new File("" + id + ".txt");
                if (idfile.exists()) {
                    // 将内容即进度读取出来
                    FileInputStream fin = new FileInputStream(idfile);
                    byte[] result = StreamTools.getBytes(fin);
                    String strinfo = new String(result);
                    if (!"".equals(strinfo) && strinfo != null) {
                        beginsize = Integer.parseInt(strinfo);
                    }
                }
                URL url = new URL(DownloadTest.path);
                HttpURLConnection conn = (HttpURLConnection) url
                        .openConnection();

                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                if (beginsize > endsize) {
                    beginsize = endsize - 1;
                }
                conn.setRequestProperty(
                        "User-Agent",
                        "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
                conn.setRequestProperty("Range", "bytes=" + beginsize + "-"
                        + endsize);
                System.out.println("线程"+id+"从" + beginsize + "开始下载" + endsize + "结束");

                File file = new File("youdao.exe");
                RandomAccessFile randomfile = new RandomAccessFile(file, "rwd");
                // 如果下载被强行中断，这保存下载的位置，
                randomfile.seek(beginsize);

                InputStream in = conn.getInputStream();
                byte[] bt = new byte[1024];

                int len = 0;
                int total = 0;
                while ((len = in.read(bt)) != -1) {
                    randomfile.write(bt, 0, len);
                    // 下载量 下载位置
                    total += len;
                    // 将位置信息保存到相应的文件
                    FileOutputStream out = new FileOutputStream(idfile);
                    out.write((beginsize + total + "").getBytes());
                    out.flush();
                    out.close();

                }
                in.close();
                randomfile.close();
                System.out.println("线程" + id + "执行完毕！");

                // 使用synchronized的代码块保count被多个线程同时访问
                synchronized (DownloadTest.class) {
                    DownloadTest.threadcount++;
                    if (DownloadTest.threadcount >= 3) {
                        System.out.println("所有的线程都执行完毕了");
                        for (int i = 0; i < 3; i++) {
                            File deleteFile = new File(i + ".txt");
                            System.out.println(i + "删除" + deleteFile.delete());
                        }
                    }

                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

 四、移植到Android上

       功能：1、界面上有下载进度条，可以记录下载进度

               2、设置暂停按钮（通过设置flag控制）

package com.lewu.download;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.Toast;

public class MutiDownloadAndActivity extends Activity implements
        OnClickListener {
    private EditText down_edit;
    private Button down_sure;
    private Button down_stop;
    private ProgressBar bar;
    private int totalsize;
    private boolean flag=true;
    public static int threadcount = 0;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        down_edit = (EditText) findViewById(R.id.down_edit);
        down_sure = (Button) findViewById(R.id.down_sure);
        down_stop = (Button) findViewById(R.id.down_stop);
        bar = (ProgressBar) findViewById(R.id.progressBar1);

        down_sure.setOnClickListener(this);
        down_stop.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
        case R.id.down_sure:

            String path = down_edit.getText().toString().trim();
            System.out.println(path + ">>>>>>>>>>");
            if ("".equals(path)) {
                Toast.makeText(this, "路径不能为空", 0);
                return;
            } else {
                down_stop.setClickable(true);
                down_stop.setEnabled(true);
                try {
                    URL url = new URL(path);
                    HttpURLConnection conn = (HttpURLConnection) url
                            .openConnection();
                    conn.setRequestMethod("GET");
                    conn.setConnectTimeout(5000);
                    conn.setRequestProperty(
                            "User-Agent",
                            "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
                    int length = conn.getContentLength();
                    System.err.println("文件的长度为" + length);
                    //设置进度条的进度
                    bar.setMax(length);
                    File file = new File(
                            Environment.getExternalStorageDirectory(),
                            getFileName(path));
                    RandomAccessFile randomfile = new RandomAccessFile(file,
                            "rwd");
                    randomfile.setLength(length);

                    // 创建三个线程 :线程分配下载资源
                    int blocksize = length / 3;
                    for (int i = 1; i <= 3; i++) {
                        // 线程执行下载操作 ，需要定位下载的位置，则需要设置一些参数
                        int beginsize = (i - 1) * blocksize;
                        int endsize = i * blocksize - 1;
                        if (i == 3) {
                            endsize = length;
                        }
                        int id = i;

                        // 启动线程
                        new Thread(new DownloadThread(id, beginsize, endsize,
                                path)).start();

                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
                break;
            }

        case R.id.down_stop:
            flag = false;
            down_stop.setClickable(true);
            down_stop.setEnabled(true);

            break;

        }
    }

    class DownloadThread implements Runnable {

        private int id;
        private int beginsize;
        private int endsize;
        private String path;

        public DownloadThread(int id, int beginsize, int endsize, String path) {
            this.id = id;
            this.beginsize = beginsize;
            this.endsize = endsize;
            this.path = path;
        }

        @Override
        public void run() {
            try {
                flag = true;
                // 每一个线程在创建的时候 都创建一个名为id.text的文件用来保存下载进度
                File idfile = new File("/mnt/sdcard/" + id + ".txt");
                if (idfile.exists()) {
                    // 将内容即进度读取出来
                    FileInputStream fin = new FileInputStream(idfile);
                    byte[] result = StreamTools.getBytes(fin);
                    String strinfo = new String(result);
                    if (!"".equals(strinfo) && strinfo != null) {
                        beginsize = Integer.parseInt(strinfo);
                    }
                }
                URL url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection) url
                        .openConnection();

                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                if (beginsize > endsize) {
                    beginsize = endsize - 1;
                }
                conn.setRequestProperty(
                        "User-Agent",
                        "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
                conn.setRequestProperty("Range", "bytes=" + beginsize + "-"
                        + endsize);
                System.out.println("线程" + id + "从" + beginsize + "开始下载"
                        + endsize + "结束");

                File file = new File(Environment.getExternalStorageDirectory(),
                        getFileName(path));
                RandomAccessFile randomfile = new RandomAccessFile(file, "rwd");
                // 如果下载被强行中断，这保存下载的位置，
                randomfile.seek(beginsize);

                InputStream in = conn.getInputStream();
                byte[] bt = new byte[1024];

                int len = 0;
                int total = 0;
                while ((len = in.read(bt)) != -1) {
                    randomfile.write(bt, 0, len);
                    // 下载量 下载位置
                    total += len;

                    // 设置进度条的进度
                    setProgressbarProgress(len);

                    // 将位置信息保存到相应的文件
                    FileOutputStream out = new FileOutputStream(idfile);
                    out.write((beginsize + total + "").getBytes());
                    out.flush();
                    out.close();
                    if(!flag){
                        return;
                    }

                }
                in.close();
                randomfile.close();
                System.out.println("线程" + id + "执行完毕！");

                // 使用synchronized的代码块保count被多个线程同时访问
                synchronized (MutiDownloadAndActivity.class) {
                    MutiDownloadAndActivity.threadcount++;
                    if (MutiDownloadAndActivity.threadcount >= 3) {
                        System.out.println("所有的线程都执行完毕了");
                        for (int i = 1; i <= 3; i++) {
                            File deleteFile = new File("/mnt/sdcard/" + i
                                    + ".txt");
                            System.out.println(i + "删除" + deleteFile.delete());
                        }
                    }

                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static String getFileName(String path) {
        int index = path.lastIndexOf("/") + 1;
        return path.substring(index);

    }

    public void setProgressbarProgress(int len) {
        if (len != 0) {
            totalsize += len;
            bar.setProgress(totalsize);
        }

    }

}

      下载界面：