Android多線程斷點續傳下載

學習了多線程下載，而且可以斷點續傳的邏輯，線程數量可以自己選擇，但是線程數量過多手機就承受不起，導致閃退，好在有斷點續傳。

步驟寫在了代碼的注釋里。大概就是獲取服務器文件的大小，在本地新建一個相同大小的文件用來申請空間，然后將服務器的文件讀下來寫到申請的文件中去。若開多線程，將文件分塊，計算每個線程下載的開始位置和結束位置。若斷點傳輸，則保存斷開后下載的位置，下次將此位置賦給開始下載的位置即可。細節見代碼。

下面是效果圖：

 

 

 

布局文件activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <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"
            android:text="http://10.173.29.234/test.exe" />

        <EditText
            android:id="@+id/et_threadCount"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="請輸入線程數量" />

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

        <LinearLayout
            android:id="@+id/ll_pb"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#455eee"
            android:orientation="vertical">

        </LinearLayout>
    </LinearLayout>

</android.support.constraint.ConstraintLayout>

創建布局文件，用來動態顯示每個線程的進度條

layout.xml:

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

MainActivity.java:

import...;

public class MainActivity extends AppCompatActivity {

    private EditText et_path;
    private EditText et_threadCount;
    private LinearLayout ll_pb;
    private String path;

    private static int runningThread;// 代表正在運行的線程
    private int threadCount;
    private List<ProgressBar> pbList;//集合存儲進度條的引用

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

        et_path = findViewById(R.id.et_path);
        et_threadCount = findViewById(R.id.et_threadCount);
        ll_pb = findViewById(R.id.ll_pb);
        //添加一個進度條的引用
        pbList = new ArrayList<ProgressBar>();
    }

    //點擊按鈕實現下載邏輯
    public void click(View view) {
        //獲取下載路徑
        path = et_path.getText().toString().trim();
        //獲取線程數量
        String threadCounts = et_threadCount.getText().toString().trim();
        //移除以前的進度條添加新的進度條
        ll_pb.removeAllViews();
        threadCount = Integer.parseInt(threadCounts);
        pbList.clear();
        for (int i = 0; i < threadCount; i++) {
            ProgressBar v = (ProgressBar) View.inflate(getApplicationContext(), R.layout.layout, null);

            //把v添加到幾何中
            pbList.add(v);

            //動態獲取進度條
            ll_pb.addView(v);
        }

        //java邏輯移植
        new Thread() {
            @Override
            public void run() {
                /*************/
                System.out.println("你好");
                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();
                        // 把運行線程的數量賦值給runningThread
                        runningThread = threadCount;

                        System.out.println("length=" + length);
                        // 創建一個和服務器的文件一樣大小的文件，提前申請空間
                        RandomAccessFile randomAccessFile = new RandomAccessFile(getFileName(path), "rw");
                        randomAccessFile.setLength(length);
                        // 算出每個線程下載的大小
                        int blockSize = length / threadCount;
                        // 計算每個線程下載的開始位置和結束位置
                        for (int i = 0; i < length; i++) {
                            int startIndex = i * blockSize;// 開始位置
                            int endIndex = (i + 1) * blockSize;// 結束位置
                            // 特殊情況就是最后一個線程
                            if (i == threadCount - 1) {
                                // 說明是最后一個線程
                                endIndex = length - 1;
                            }
                            // 開啟線程去服務器下載
                            DownLoadThread downLoadThread = new DownLoadThread(startIndex, endIndex, i);
                            downLoadThread.start();

                        }

                    }
                } catch (MalformedURLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                /*************/
            }
        }.start();

    }

    private class DownLoadThread extends Thread {
        // 通過構造方法吧每個線程的開始位置和結束位置傳進來
        private int startIndex;
        private int endIndex;
        private int threadID;
        private int PbMaxSize;//代表當前下載（進度條）的最大值
        private int pblastPosition;//如果中斷過，這是進度條上次的位置

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

        }

        @Override
        public void run() {
            // 實現去服務器下載文件
            try {
                //計算進度條最大值
                PbMaxSize = endIndex - startIndex;
                URL url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                // 如果中間斷過，接着上次的位置繼續下載，聰慧文件中讀取上次下載的位置
                File file = new File(getFileName(path) + threadID + ".txt");
                if (file.exists() && file.length() > 0) {
                    FileInputStream fis = new FileInputStream(file);
                    BufferedReader bufr = new BufferedReader(new InputStreamReader(fis));
                    String lastPosition = bufr.readLine();
                    int lastPosition1 = Integer.parseInt(lastPosition);

                    //賦值給進度條位置
                    pblastPosition = lastPosition1 - startIndex;
                    // 改變一下startIndex的值
                    startIndex = lastPosition1 + 1;
                    System.out.println("線程id：" + threadID + "真實下載的位置：" + lastPosition + "-------" + endIndex);

                    bufr.close();
                    fis.close();

                }

                conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);
                int code = conn.getResponseCode();
                if (code == 206) {
                    // 隨機讀寫文件對象
                    RandomAccessFile raf = new RandomAccessFile(getFileName(path), "rw");
                    // 每個線程從自己的位置開始寫

                    raf.seek(startIndex);
                    InputStream in = conn.getInputStream();
                    // 把數據寫到文件中
                    int len = -1;
                    byte[] buffer = new byte[1024];
                    int totle = 0;// 代表當前線程下載的大小
                    while ((len = in.read(buffer)) != -1) {
                        raf.write(buffer, 0, len);
                        totle += len;

                        // 實現斷點續傳就是把當前線程下載的位置保存起來，下次再下載的時候按照上次下載的位置繼續下載
                        int currentThreadPosition = startIndex + totle;// 存到一個txt文本中
                        // 用來存儲當前線程當前下載的位置
                        RandomAccessFile raff = new RandomAccessFile(getFileName(path) + threadID + ".txt", "rwd");
                        raff.write(String.valueOf(currentThreadPosition).getBytes());
                        raff.close();

                        //設置進度條當前的進度
                        pbList.get(threadID).setMax(PbMaxSize);
                        pbList.get(threadID).setProgress(pblastPosition + totle);
                    }
                    raf.close();
                    System.out.println("線程ID:" + threadID + "下載完成");
                    // 將產生的txt文件刪除，每個線程下載完成的具體時間不知道
                    synchronized (DownLoadThread.class) {
                        runningThread--;
                        if (runningThread == 0) {
                            //說明線程執行完畢
                            for (int i = 0; i < threadCount; i++) {

                                File filedel = new File(getFileName(path) + i + ".txt");
                                filedel.delete();
                            }

                        }

                    }

                }
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    }

    public String getFileName(String path) {
        int start = path.lastIndexOf("/") + 1;
        String subString = path.substring(start);
        String fileName = "/data/data/com.lgqrlchinese.heima76android_11_mutildownload/" + subString;
        return fileName;

    }
}

在清單文件中添加以下權限

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

筆記結束

 

bug非常多，而且誰又願意寫這么繁瑣的邏輯，所以找到別人寫開源框架，下一篇將會作下筆記