Android 多线程断点下载

package com.itheima.mutiledownloader;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.renderscript.Program.TextureType;
import android.text.TextUtils;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import android.widget.Toast;

public class MainActivity extends Activity {
        protected static final int DOWNLOAD_ERROR = ;
        private static final int THREAD_DOWNLOAD_ERROR = ;
        public static final int DONWLOAD_FINISH = ;
        private EditText et_path;
        private EditText et_number;
        private LinearLayout ll_pb;
        private String path;
        private static int threadCount = ;
        private static int blockSize = ;
        private static int livingThread = ;

        private List<ProgressBar> pbs;

        private Handler handler = new Handler() {
                public void handleMessage(android.os.Message msg) {
                        switch (msg.what) {
                        case DOWNLOAD_ERROR:
                                Toast.makeText(getApplicationContext(), "初始化下载失败", ).show();
                                break;
                        case THREAD_DOWNLOAD_ERROR:
                                String str = (String) msg.obj;
                                Toast.makeText(getApplicationContext(), str, ).show();
                                break;
                        case DONWLOAD_FINISH:
                                Toast.makeText(getApplicationContext(), "下载完毕", ).show();
                                findViewById(R.id.bt).setEnabled(true);
                                break;
                        }
                };
        };

        @Override
        protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_main);
                et_path = (EditText) findViewById(R.id.et_path);
                et_number = (EditText) findViewById(R.id.et_number);
                ll_pb = (LinearLayout) findViewById(R.id.ll_pb);

        }

        public void click(View view) {
                path = et_path.getText().toString().trim();
                String strNumber = et_number.getText().toString().trim();
                if (TextUtils.isEmpty(path) || TextUtils.isEmpty(strNumber)) {
                        Toast.makeText(this, "请输入参数", ).show();
                        return;
                } else {
                        // 下载的线程的个数
                        threadCount = Integer.parseInt(strNumber);
                        pbs = new ArrayList<ProgressBar>();
                        ll_pb.removeAllViews();
                        for (int i = ; i < threadCount; i++) {
                                ProgressBar pb = (ProgressBar) View.inflate(
                                                getApplicationContext(), R.layout.pb_item, null);
                                pb.setPadding(, , , );
                                ll_pb.addView(pb, LayoutParams.MATCH_PARENT, );
                                //在集合里面添加进度条的引用.
                                pbs.add(pb);
                        }
                        findViewById(R.id.bt).setEnabled(false);
                        new Thread() {
                                public void run() {
                                        try {
                                                URL url = new URL(path);
                                                HttpURLConnection conn = (HttpURLConnection) url
                                                                .openConnection();
                                                conn.setRequestMethod("GET");
                                                conn.setConnectTimeout();
                                                // 服务器文件的长度
                                                int length = conn.getContentLength();
                                                // 本地创建一个大小跟服务器一样的文件
                                                RandomAccessFile raf = new RandomAccessFile(Environment
                                                                .getExternalStorageDirectory()
                                                                .getAbsolutePath()
                                                                + "/" + getFileName(path), "rw");
                                                raf.setLength(length);
                                                System.out.println("文件的总长度:" + length);
                                                // 计算每个线程下载的位置.
                                                blockSize = length / threadCount;
                                                System.out.println("每一个块的平均长度:" + blockSize);
                                                livingThread = threadCount;
                                                for (int i = ; i <= threadCount; i++) {
                                                        int startIndex = (i - ) * blockSize;
                                                        int endIndex = i * blockSize - ;
                                                        if (i == threadCount) {
                                                                endIndex = length;
                                                        }
                                                        //设置进度条的总进度
                                                        pbs.get(i-).setMax(endIndex-startIndex);
                                                        new Thread(
                                                                        new DownLoadTask(i, startIndex, endIndex))
                                                                        .start();
                                                }
                                        } catch (Exception e) {
                                                e.printStackTrace();
                                                Message msg = Message.obtain();
                                                msg.what = DOWNLOAD_ERROR;
                                                handler.sendMessage(msg);
                                        }
                                };
                        }.start();

                }
        }

        /**
         * 获取下载的文件的名称
         *
         * @param path
         * @return
         */
        private static String getFileName(String path) {
                int start = path.lastIndexOf("/") + ;
                return path.substring(start);
        }

        private class DownLoadTask implements Runnable {

                private int id;
                private int startIndex;
                private int endIndex;

                public DownLoadTask(int id, int startIndex, int endIndex) {
                        this.id = id;
                        this.startIndex = startIndex;
                        this.endIndex = endIndex;
                }

                @Override
                public void run() {
                        try {
                                int downloadCount =   ;
                                URL url = new URL(path);
                                HttpURLConnection conn = (HttpURLConnection) url
                                                .openConnection();
                                conn.setRequestMethod("GET");
                                conn.setConnectTimeout();
                                // 在每次下载之前,检查是否存在已经下载大小的记录文件.
                                File f = new File(Environment.getExternalStorageDirectory()
                                                .getAbsolutePath()
                                                + "/"
                                                + getFileName(path)
                                                + id
                                                + ".txt");
                                if (f.exists() && f.length() > ) {
                                        FileInputStream fis = new FileInputStream(f);
                                        BufferedReader br = new BufferedReader(
                                                        new InputStreamReader(fis));
                                        // 已经下载的大小.
                                        downloadCount = Integer.parseInt(br.readLine());
                                        startIndex += downloadCount;
                                        br.close();
                                        fis.close();
                                }
                                conn.setRequestProperty("Range", "bytes=" + startIndex + "-"
                                                + endIndex);
                                System.out.println("线程id:" + id + " 下载的位置:" + startIndex
                                                + "~~~" + endIndex);
                                RandomAccessFile raf = new RandomAccessFile(Environment
                                                .getExternalStorageDirectory().getAbsolutePath()
                                                + "/"
                                                + getFileName(path), "rwd");
                                InputStream is = conn.getInputStream();
                                // 指定线程下载存放文件的开始位置.
                                raf.seek(startIndex);
                                int len = ;
                                byte[] buffer = new byte[];
                                int total = ;// 记录当前线程下载的大小.
                                while ((len = is.read(buffer)) != -) {
                                        File file = new File(Environment
                                                        .getExternalStorageDirectory().getAbsolutePath()
                                                        + "/" + getFileName(path) + id + ".txt");
                                        RandomAccessFile positionRaf = new RandomAccessFile(file,
                                                        "rwd");
                                        raf.write(buffer, , len);
                                        total += len;
                                        positionRaf.write(String.valueOf(total).getBytes());
                                        positionRaf.close();
                                        pbs.get(id-).setProgress(total+downloadCount);
                                }
                                raf.close();
                                is.close();
                                System.out.println("线程:" + id + "下载完毕...");
                        } catch (Exception e) {
                                e.printStackTrace();
                                Message msg = Message.obtain();
                                msg.what = THREAD_DOWNLOAD_ERROR;
                                msg.obj = "线程:" + id + "下载失败.";
                                handler.sendMessage(msg);
                        } finally {
                                synchronized (MainActivity.this) {
                                        livingThread--;
                                        if (livingThread <= ) {
                                                System.out.println("全部下载完毕...");
                                                Message msg = Message.obtain();
                                                msg.what = DONWLOAD_FINISH;
                                                handler.sendMessage(msg);
                                                for (int i = ; i <= threadCount; i++) {
                                                        File f = new File(Environment
                                                                        .getExternalStorageDirectory()
                                                                        .getAbsolutePath()
                                                                        + "/" + getFileName(path) + i + ".txt");
                                                        System.out.println(f.delete());
                                                }
                                        }
                                }

                        }
                }
        }
}