安卓開發：多線程斷點續傳下載文件

一個簡單的界面：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <EditText
        android:id="@+id/et_path"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="請輸入下載路徑（網址）：" />

    <EditText
        android:id="@+id/et_threadCount"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="請輸入開啟線程數量（建議不超過5）：" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click"
        android:text="開始下載" />

    
    <LinearLayout 
        android:id="@+id/ll_pb"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        ></LinearLayout>
</LinearLayout>

item.xml:

<?xml version="1.0" encoding="utf-8"?>
<ProgressBar xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/progressBar1"
    style="?android:attr/progressBarStyleHorizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

代碼：

package org.dreamtech.download;

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 java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.view.View;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ProgressBar;

public class MainActivity extends Activity {

    private EditText et_path;
    private EditText et_threadCount;
    private LinearLayout ll_pb_layout;
    private static int runningThread;
    private String path;
    private int threadCount;
    private List<ProgressBar> pbLists;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        et_path = (EditText) findViewById(R.id.et_path);
        et_threadCount = (EditText) findViewById(R.id.et_threadCount);
        ll_pb_layout = (LinearLayout) findViewById(R.id.ll_pb);

        pbLists = new ArrayList<ProgressBar>();

    }

    public void click(View v) {
        path = et_path.getText().toString().trim();
        threadCount = Integer.parseInt(et_threadCount.getText().toString()
                .trim());
        ll_pb_layout.removeAllViews();
        pbLists.clear();
        for (int i = 0; i < threadCount; i++) {
            ProgressBar pbView = (ProgressBar) View.inflate(
                    getApplicationContext(), R.layout.item, null);

            pbLists.add(pbView);

            ll_pb_layout.addView(pbView);
        }
        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) {

                        int length = conn.getContentLength();

                        runningThread = threadCount;

                        System.out.println("length:" + length);

                        RandomAccessFile rafAccessFile = new RandomAccessFile(
                                getFilename(path), "rw");
                        rafAccessFile.setLength(length);

                        int blockSize = length / threadCount;

                        for (int i = 0; i < threadCount; i++) {
                            int startIndex = i * blockSize;
                            int endIndex = (i + 1) * blockSize - 1;

                            if (i == threadCount - 1) {

                                endIndex = length - 1;

                            }

                            DownLoadThread downLoadThread = new DownLoadThread(
                                    startIndex, endIndex, i);
                            downLoadThread.start();

                        }

                    }

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

    private class DownLoadThread extends Thread {

        private int startIndex;
        private int endIndex;
        private int threadId;
        private int PbMaxSize;
        private int pblastPosition;

        public DownLoadThread(int startIndex, int endIndex, int threadId) {
            this.startIndex = startIndex;
            this.endIndex = endIndex;
            this.threadId = threadId;
        }

        @Override
        public void run() {

            try {
                PbMaxSize = endIndex - startIndex;

                URL url = new URL(path);

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

                conn.setRequestMethod("GET");

                conn.setConnectTimeout(5000);

                File file = new File(Environment.getExternalStorageDirectory()
                        .getPath()
                        + "/"
                        + getFilename(path)
                        + threadId
                        + ".txt");
                if (file.exists() && file.length() > 0) {
                    FileInputStream fis = new FileInputStream(file);
                    BufferedReader bufr = new BufferedReader(
                            new InputStreamReader(fis));
                    String lastPositionn = bufr.readLine();
                    int lastPosition = Integer.parseInt(lastPositionn);

                    pblastPosition = lastPosition - startIndex;

                    startIndex = lastPosition + 1;

                    fis.close();
                }

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

                int code = conn.getResponseCode();

                if (code == 206) {

                    RandomAccessFile raf = new RandomAccessFile(
                            getFilename(path), "rw");

                    raf.seek(startIndex);

                    InputStream in = conn.getInputStream();

                    int len = -1;
                    byte[] buffer = new byte[1024 * 1024];

                    int total = 0;

                    while ((len = in.read(buffer)) != -1) {
                        raf.write(buffer, 0, len);

                        total += len;
                        int currentThreadPosition = startIndex + total;

                        RandomAccessFile raff = new RandomAccessFile(
                                getFilename(path) + threadId + ".txt", "rwd");
                        raff.write(String.valueOf(currentThreadPosition)
                                .getBytes());
                        raff.close();

                        pbLists.get(threadId).setMax(PbMaxSize);
                        pbLists.get(threadId).setProgress(
                                pblastPosition + total);

                    }
                    raf.close();

                    synchronized (DownLoadThread.class) {
                        runningThread--;
                        if (runningThread == 0) {
                            for (int i = 0; i < threadCount; i++) {
                                File delteFile = new File(getFilename(path) + i
                                        + ".txt");
                                delteFile.delete();
                            }

                        }
                    }

                }

            } catch (Exception e) {
            }

        }
    }

    public String getFilename(String path) {

        int start = path.lastIndexOf("/") + 1;
        String subString = path.substring(start);
        String filename = Environment.getExternalStorageDirectory().getPath()+"/"+subString;
        
        return filename;
    }
}

開許可權：

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>