網絡編程之PC版與Android手機版帶斷點續傳的多線程下載

一、多線程下載

        多線程下載就是搶占服務器資源

        原理：服務器CPU 分配給每條線程的時間片相同，服務器帶寬平均分配給每條線程，所以客戶端開啟的線程越多，就能搶占到更多的服務器資源。

        

       1、設置開啟線程數，發送http請求到下載地址，獲取下載文件的總長度

          然后創建一個長度一致的臨時文件，避免下載到一半存儲空間不夠了，並計算每個線程下載多少數據       

       2、計算每個線程下載數據的開始和結束位置

          再次發送請求，用 Range 頭請求開始位置和結束位置的數據

       3、將下載到的數據，存放至臨時文件中

       4、帶斷點續傳的多線程下載

          定義一個int變量，記錄每條線程下載的數據總長度，然后加上該線程的下載開始位置，得到的結果就是下次下載時，該線程的開始位置，把得到的結果存入緩存文件，當文件下載完成，刪除臨時進度文件。

public class MultiDownload {

    static int ThreadCount = 3;
    static int finishedThread = 0;
    //確定下載地址
    static String filename = "EditPlus.exe";
    static String path = "http://192.168.3.45:8080/"+filename;
    public static void main(String[] args) {
        //1、發送get請求，去獲得下載文件的長度
        try {
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(5000);
            
            if (conn.getResponseCode()==200) {
                //如果請求成功，拿到所請求資源文件的長度
                int length = conn.getContentLength();
                
                //2、生成一個與原文件同樣的大小的臨時文件，以免下載一半存儲空間不夠了
                File file = new File(filename);//演示，所以將保存的文件目錄放在工程的同目錄
                //使用RandomAccessFile 生成臨時文件，可以用指針定位文件的任意位置，
                //而且能夠實時寫到硬件底層設備，略過緩存，這對下載文件是突然斷電等意外是有好處的
                RandomAccessFile  raf = new RandomAccessFile(file, "rwd");//rwd, 實時寫到底層設備
                //設置臨時文件的大小
                raf.setLength(length);
                raf.close();
                
                //3、計算出每個線程應該下載多少個字節
                int size = length/ThreadCount;//如果有余數，負責最后一部分的線程負責下砸
                
                //開啟多線程
                for (int threadId = 0; threadId < ThreadCount; threadId++) {
                    //計算每個線程下載的開始位置和結束位置
                    int startIndex = threadId*size;  // 開始 = 線程id * size
                    int endIndex = (threadId+1)*size - 1; //結束 = （線程id + 1)*size - 1
                    //如果是最后一個線程，那么結束位置寫死為文件結束位置
                    if (threadId == ThreadCount - 1) {
                        endIndex = length - 1;
                    }
                    
                    //System.out.println("線程"+threadId+"的下載區間是： "+startIndex+"----"+endIndex);
                    new DownloadThread(startIndex,endIndex,threadId).start();
                }
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class DownloadThread extends Thread{
    
    private int startIndex;
    private int endIndex;
    private int threadId;

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

    @Override
    public void run() {
         //每個線程再次發送http請求，下載自己對應的那部分數據
        try {
            File progressFile = new File(threadId+".txt");
            //判斷進度文件是否存在，如果存在，則接着斷點繼續下載，如果不存在，則從頭下載
            if (progressFile.exists()) {
                FileInputStream fis = new FileInputStream(progressFile);
                BufferedReader br = new BufferedReader(new InputStreamReader(fis));
                //從進度文件中度取出上一次下載的總進度，然后與原本的開始進度相加，得到新的開始進度
                startIndex += Integer.parseInt(br.readLine());
                fis.close();
            }
            System.out.println("線程"+threadId+"的下載區間是:"+startIndex+"----"+endIndex);
            
            //4、每個線程發送http請求自己的數據
            URL url = new URL(MultiDownload.path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(5000);
            //設置本次http請求所請求的數據的區間
            conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
            
            //請求部分數據，響應碼是206
            if (conn.getResponseCode()==206) {
                //此時，流里只有ThreadCount分之一的原文件數據
                InputStream is = conn.getInputStream();
                byte[] b = new byte[1024];
                int len = 0;
                int total = 0;//total 用於保存斷點續傳的斷點
                //拿到臨時文件的輸出流
                File file = new File(MultiDownload.filename);
                RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                //把文件的寫入位置移動至 startIndex
                raf.seek(startIndex);
                
                while ((len = is.read(b))!=-1) {
                    //每次讀取流里數據之后，同步把數據寫入臨時文件
                    raf.write(b, 0, len);
                    total += len;
                    
                    //System.out.println("線程" + threadId + "下載了" + total);
                    //生成一個一個專門用來記錄下載進度的臨時文件
                    RandomAccessFile progressRaf = new RandomAccessFile(progressFile, "rwd");
                    progressRaf.write((total+"").getBytes());
                    progressRaf.close();
                }
                System.out.println("線程"+threadId+"下載完了---------------------");
                raf.close();
                
                //當所有的線程下載完之后，將進度文件刪除
                MultiDownload.finishedThread++;
                synchronized (MultiDownload.path) {//所有線程使用同一個鎖
                    if (MultiDownload.finishedThread==MultiDownload.ThreadCount) {
                        for (int i = 0; i < MultiDownload.ThreadCount; i++) {
                            File f = new File(i+".txt");
                            f.delete();
                        }
                        MultiDownload.finishedThread=0;
                    }
                }
            }    
        } catch (Exception e) {
            e.printStackTrace();
        }
        
    }
}

 

二、Android手機版帶斷點續傳的多線程下載

      Android手機版的帶斷點續傳的多線程下載邏輯與PC版的幾乎一樣，只不過在Android手機中耗時操作不能放在主線程，網絡下載屬於耗時操作，所以多線程下載要在Android中開啟一個子線程執行。 並使用消息隊列機制刷新文本進度條。

public class MainActivity extends Activity {
    
    static int ThreadCount = 3;
    static int FinishedThread = 0;
    int currentProgess;
    static String Filename = "QQPlayer.exe";
    static String Path = "http://192.168.3.45:8080/"+Filename;
    
    static MainActivity ma;
    static ProgressBar pb;
    static TextView tv;
    static Handler handler = new Handler(){
        public void handleMessage(android.os.Message msg){
            tv.setText((long)pb.getProgress()*100 /pb.getMax()  +"%");
        };
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        ma = this;
        pb = (ProgressBar) findViewById(R.id.pb);
        tv = (TextView) findViewById(R.id.tv);
    }
    
    public void download(View v){
        
        Thread t = new Thread(){
            
            @Override
            public void run() {
                //發送http請求獲取文件的長度，創建臨時文件
                try {
                    URL url= new URL(Path);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setRequestMethod("GET");
                    conn.setConnectTimeout(5000);
                    conn.setReadTimeout(5000);
                    
                    if (conn.getResponseCode()==200) {
                        int length = conn.getContentLength();
                        
                        //設置進度條的最大值就是原文件的總長度
                        pb.setMax(length);
                        
                        //生成一個與原文件相同大小的臨時文件
                        File file = new File(Environment.getExternalStorageDirectory(),Filename);
                        RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                        raf.setLength(length);
                        raf.close();
                        
                        //計算每個線程需要下載的數據大小
                        int size = length/ThreadCount;
                        //開啟多線程
                        for (int threadId = 0; threadId < ThreadCount; threadId++) {
                            int startIndex = threadId*size;
                            int endIndex = (threadId + 1)*size - 1;
                            if (threadId==ThreadCount - 1) {
                                endIndex = length - 1;
                            }
                            
                            new DownloadThread(startIndex, endIndex, threadId).start();
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        };
        t.start();
    }
    
    class DownloadThread extends Thread{
        private int startIndex;
        private int endIndex;
        private int threadId;
        
        public DownloadThread(int startIndex, int endIndex, int threadId) {
            super();
            this.startIndex = startIndex;
            this.endIndex = endIndex;
            this.threadId = threadId;
        }
        
        @Override
        public void run() {
            // 每個線程發送http請求自己的數據
            try{
                //先判斷是不是斷點續傳
                File progessFile = new File(Environment.getExternalStorageDirectory(),threadId+".txt");
                if (progessFile.exists()) {
                    FileReader fr = new FileReader(progessFile);
                    BufferedReader br = new BufferedReader(fr);
                    int lastProgess = Integer.parseInt(br.readLine());
                    startIndex += lastProgess;
                    
                    //把上次下載的進度顯示至進度條
                    currentProgess +=lastProgess;
                    pb.setProgress(currentProgess);
                    //發消息，讓主線程刷新文本進度
                    handler.sendEmptyMessage(1);
                    
                    br.close();
                    fr.close();
                }
                
                URL url = new URL(Path);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                conn.setReadTimeout(5000);
                conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
                
                if (conn.getResponseCode()==206) {
                    InputStream is = conn.getInputStream();
                    byte[] buffer = new byte[1024];
                    int len = 0;
                    int total = 0;
                    
                    File file = new File(Environment.getExternalStorageDirectory(),Filename);
                    RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                    raf.seek(startIndex);
                    
                    while ((len = is.read(buffer))!= -1) {
                        raf.write(buffer, 0, len);
                        total += len;
                        
                        //每次讀取流里數據之后，把本次讀取的數據的長度顯示至進度條
                        currentProgess += len;
                        pb.setProgress(currentProgess);
                        //發消息，讓主線程刷新文本進度
                        handler.sendEmptyMessage(1);
                        //生成臨時文件保存下載進度，用於斷點續傳，在所有線程現在完畢后刪除臨時文件
                        RandomAccessFile progressRaf = new RandomAccessFile(progessFile, "rwd");
                        progressRaf.write((total+"").getBytes());
                        progressRaf.close();
                    }
                    raf.close();
                    System.out.println("線程"+threadId+"下載完了");
                    
                    //當所有線程都下在完了之后，刪除臨時進度文件
                    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) {
                e.printStackTrace();
            }
        }
    }
}

 

來自為知筆記(Wiz)