Android开发之多线程下载、断点续传、进度条和文本显示

代码实现了在Android环境下的多线程下载、断点续传、进度条显示和文本显示百分数：

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


import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MainActivity extends Activity {

    static int ThreadCount = 3;
    static int finishedThread = 0;
    
    int currentProgress;
    String fileName = "QQPlayer.exe";
    //确定下载地址
    String path = "http://192.168.13.13:8080/" + fileName;
    private ProgressBar pb;
    TextView tv;
    
    Handler handler = new Handler(){
        public void handleMessage(android.os.Message msg) {
            //把变量改成long，在long下运算
            tv.setText((long)pb.getProgress() * 100 / pb.getMax() + "%");
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        pb = (ProgressBar) findViewById(R.id.pb);
        tv = (TextView) findViewById(R.id.tv);
    }

    public void click(View v){
        
        Thread t = new Thread(){
            @Override
            public void run() {
                //发送get请求，请求这个地址的资源
                try {
                    URL url = new URL(path);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setRequestMethod("GET");
                    conn.setConnectTimeout(5000);
                    conn.setReadTimeout(5000);
                    
                    if(conn.getResponseCode() == 200){
                        //拿到所请求资源文件的长度
                        int length = conn.getContentLength();
                        
                        //设置进度条的最大值就是原文件的总长度
                        pb.setMax(length);
                        
                        File file = new File(Environment.getExternalStorageDirectory(), fileName);
                        //生成临时文件
                        RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                        //设置临时文件的大小
                        raf.setLength(length);
                        raf.close();
                        //计算出每个线程应该下载多少字节
                        int size = length / ThreadCount;
                        
                        for (int i = 0; i < ThreadCount; i++) {
                            //计算线程下载的开始位置和结束位置
                            int startIndex = i * size;
                            int endIndex = (i + 1) * size - 1;
                            //如果是最后一个线程，那么结束位置写死
                            if(i == ThreadCount - 1){
                                endIndex = length - 1;
                            }
//                            System.out.println("线程" + i + "的下载区间是：" + startIndex + "---" + endIndex);
                            new DownLoadThread(startIndex, endIndex, i).start();
                        }
                    }
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        };
        t.start();
    }
    
    class DownLoadThread extends Thread{
        int startIndex;
        int endIndex;
        int threadId;
        
        public DownLoadThread(int startIndex, int endIndex, int threadId) {
            super();
            this.startIndex = startIndex;
            this.endIndex = endIndex;
            this.threadId = threadId;
        }

        @Override
        public void run() {
            //再次发送http请求，下载原文件
            try {
                File progressFile = new File(Environment.getExternalStorageDirectory(), threadId + ".txt");
                //判断进度临时文件是否存在
                if(progressFile.exists()){
                    FileInputStream fis = new FileInputStream(progressFile);
                    BufferedReader br = new BufferedReader(new InputStreamReader(fis));
                    //从进度临时文件中读取出上一次下载的总进度，然后与原本的开始位置相加，得到新的开始位置
                    int lastProgress = Integer.parseInt(br.readLine());
                    startIndex += lastProgress;
                    
                    //把上次下载的进度显示至进度条
                    currentProgress += lastProgress;
                    pb.setProgress(currentProgress);
                    
                    //发送消息，让主线程刷新文本进度
                    handler.sendEmptyMessage(1);
                    fis.close();
                }
                System.out.println("线程" + threadId + "的下载区间是：" + startIndex + "---" + endIndex);
                HttpURLConnection conn;
                URL url = new URL(path);
                conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                conn.setReadTimeout(5000);
                //设置本次http请求所请求的数据的区间
                conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);
                
                //请求部分数据，相应码是206
                if(conn.getResponseCode() == 206){
                    //流里此时只有1/3原文件的数据
                    InputStream is = conn.getInputStream();
                    byte[] b = new byte[1024];
                    int len = 0;
                    int total = 0;
                    //拿到临时文件的输出流
                    File file = new File(Environment.getExternalStorageDirectory(), fileName);
                    RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                    //把文件的写入位置移动至startIndex
                    raf.seek(startIndex);
                    while((len = is.read(b)) != -1){
                        //每次读取流里数据之后，同步把数据写入临时文件
                        raf.write(b, 0, len);
                        total += len;
                        System.out.println("线程" + threadId + "下载了" + total);
                        
                        //每次读取流里数据之后，把本次读取的数据的长度显示至进度条
                        currentProgress += len;
                        pb.setProgress(currentProgress);
                        //发送消息，让主线程刷新文本进度
                        handler.sendEmptyMessage(1);
                        
                        //生成一个专门用来记录下载进度的临时文件
                        RandomAccessFile progressRaf = new RandomAccessFile(progressFile, "rwd");
                        //每次读取流里数据之后，同步把当前线程下载的总进度写入进度临时文件中
                        progressRaf.write((total + "").getBytes());
                        progressRaf.close();
                    }
                    System.out.println("线程" + threadId + "下载完毕-------------------小志参上！");
                    raf.close();
                    
                    finishedThread++;
                    synchronized (path) {
                        if(finishedThread == ThreadCount){
                            for (int i = 0; i < ThreadCount; i++) {
                                File f = new File(Environment.getExternalStorageDirectory(), i + ".txt");
                                f.delete();
                            }
                            finishedThread = 0;
                        }
                    }
                    
                }
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

}