一、多線程下載
多線程下載就是搶占服務(wù)器資源
原理：服務(wù)器CPU 分配給每條線程的時(shí)間片相同，服務(wù)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(wù)器資源。
1、設(shè)置開啟線程數(shù)，發(fā)送http請求到下載地址，獲取下載文件的總長度
然后創(chuàng)建一個(gè)長度一致的臨時(shí)文件，避免下載到一半存儲空間不夠了，并計(jì)算每個(gè)線程下載多少數(shù)據(jù)
2、計(jì)算每個(gè)線程下載數(shù)據(jù)的開始和結(jié)束位置
再次發(fā)送請求，用 Range 頭請求開始位置和結(jié)束位置的數(shù)據(jù)
3、將下載到的數(shù)據(jù)，存放至臨時(shí)文件中
4、帶斷點(diǎn)續(xù)傳的多線程下載
定義一個(gè)int變量，記錄每條線程下載的數(shù)據(jù)總長度，然后加上該線程的下載開始位置，得到的結(jié)果就是下次下載時(shí)，該線程的開始位置，把得到的結(jié)果存入緩存文件，當(dāng)文件下載完成，刪除臨時(shí)進(jìn)度文件。
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public class MultiDownload { static int ThreadCount = ; static int finishedThread = ; //確定下載地址 static String filename = "EditPlus.exe"; static String path = "http://...:/"+filename; public static void main(String[] args) { //、發(fā)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(); conn.setReadTimeout(); if (conn.getResponseCode()==) { //如果請求成功，拿到所請求資源文件的長度 int length = conn.getContentLength(); //、生成一個(gè)與原文件同樣的大小的臨時(shí)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(shí)文件，可以用指針定位文件的任意位置， //而且能夠?qū)崟r(shí)寫到硬件底層設(shè)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(shí)時(shí)寫到底層設(shè)備 //設(shè)置臨時(shí)文件的大小 raf.setLength(length); raf.close(); //、計(jì)算出每個(gè)線程應(yīng)該下載多少個(gè)字節(jié) int size = length/ThreadCount;//如果有余數(shù)，負(fù)責(zé)最后一部分的線程負(fù)責(zé)下砸 //開啟多線程 for (int threadId = ; threadId < ThreadCount; threadId++) { //計(jì)算每個(gè)線程下載的開始位置和結(jié)束位置 int startIndex = threadId*size; // 開始 = 線程id * size int endIndex = (threadId+)*size - ; //結(jié)束 = （線程id + )*size - //如果是最后一個(gè)線程，那么結(jié)束位置寫死為文件結(jié)束位置 if (threadId == ThreadCount - ) { endIndex = length - ; } //System.out.println("線程"+threadId+"的下載區(qū)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; } public void run() { //每個(gè)線程再次發(fā)送http請求，下載自己對應(yīng)的那部分?jǐn)?shù)據(jù) try { File progressFile = new File(threadId+".txt"); //判斷進(jìn)度文件是否存在，如果存在，則接著斷點(diǎn)繼續(xù)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(jìn)度文件中度取出上一次下載的總進(jìn)度，然后與原本的開始進(jìn)度相加，得到新的開始進(jìn)度 startIndex += Integer.parseInt(br.readLine()); fis.close(); } System.out.println("線程"+threadId+"的下載區(qū)間是:"+startIndex+"----"+endIndex); //、每個(gè)線程發(fā)送http請求自己的數(shù)據(jù) URL url = new URL(MultiDownload.path); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(); conn.setReadTimeout(); //設(shè)置本次http請求所請求的數(shù)據(jù)的區(qū)間 conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex); //請求部分?jǐn)?shù)據(jù)，響應(yīng)碼是 if (conn.getResponseCode()==) { //此時(shí)，流里只有ThreadCount分之一的原文件數(shù)據(jù) InputStream is = conn.getInputStream(); byte[] b = new byte[]; int len = ; int total = ;//total 用于保存斷點(diǎn)續(xù)傳的斷點(diǎn) //拿到臨時(shí)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(dòng)至 startIndex raf.seek(startIndex); while ((len = is.read(b))!=-) { //每次讀取流里數(shù)據(jù)之后，同步把數(shù)據(jù)寫入臨時(shí)文件 raf.write(b, , len); total += len; //System.out.println("線程" + threadId + "下載了" + total); //生成一個(gè)一個(gè)專門用來記錄下載進(jìn)度的臨時(shí)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(dāng)所有的線程下載完之后，將進(jìn)度文件刪除 MultiDownload.finishedThread++; synchronized (MultiDownload.path) {//所有線程使用同一個(gè)鎖 if (MultiDownload.finishedThread==MultiDownload.ThreadCount) { for (int i = ; i < MultiDownload.ThreadCount; i++) { File f = new File(i+".txt"); f.delete(); } MultiDownload.finishedThread=; } } } } catch (Exception e) { e.printStackTrace(); } }} |
二、Android手機(jī)版帶斷點(diǎn)續(xù)傳的多線程下載
Android手機(jī)版的帶斷點(diǎn)續(xù)傳的多線程下載邏輯與PC版的幾乎一樣，只不過在Android手機(jī)中耗時(shí)操作不能放在主線程，網(wǎng)絡(luò)下載屬于耗時(shí)操作，所以多線程下載要在Android中開啟一個(gè)子線程執(zhí)行。并使用消息隊(duì)列機(jī)制刷新文本進(jìn)度條。
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public class MainActivity extends Activity { static int ThreadCount = ; static int FinishedThread = ; int currentProgess; static String Filename = "QQPlayer.exe"; static String Path = "http://...:/"+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()* /pb.getMax() +"%"); }; }; 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(){ public void run() { //發(fā)送http請求獲取文件的長度，創(chuàng)建臨時(shí)文件 try { URL url= new URL(Path); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(); conn.setReadTimeout(); if (conn.getResponseCode()==) { int length = conn.getContentLength(); //設(shè)置進(jìn)度條的最大值就是原文件的總長度 pb.setMax(length); //生成一個(gè)與原文件相同大小的臨時(shí)文件 File file = new File(Environment.getExternalStorageDirectory(),Filename); RandomAccessFile raf = new RandomAccessFile(file, "rwd"); raf.setLength(length); raf.close(); //計(jì)算每個(gè)線程需要下載的數(shù)據(jù)大小 int size = length/ThreadCount; //開啟多線程 for (int threadId = ; threadId < ThreadCount; threadId++) { int startIndex = threadId*size; int endIndex = (threadId + )*size - ; if (threadId==ThreadCount - ) { endIndex = length - ; } 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; } public void run() { // 每個(gè)線程發(fā)送http請求自己的數(shù)據(jù) try{ //先判斷是不是斷點(diǎn)續(xù)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(jìn)度顯示至進(jìn)度條 currentProgess +=lastProgess; pb.setProgress(currentProgess); //發(fā)消息，讓主線程刷新文本進(jìn)度 handler.sendEmptyMessage(); br.close(); fr.close(); } URL url = new URL(Path); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(); conn.setReadTimeout(); conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex); if (conn.getResponseCode()==) { InputStream is = conn.getInputStream(); byte[] buffer = new byte[]; int len = ; int total = ; File file = new File(Environment.getExternalStorageDirectory(),Filename); RandomAccessFile raf = new RandomAccessFile(file, "rwd"); raf.seek(startIndex); while ((len = is.read(buffer))!= -) { raf.write(buffer, , len); total += len; //每次讀取流里數(shù)據(jù)之后，把本次讀取的數(shù)據(jù)的長度顯示至進(jìn)度條 currentProgess += len; pb.setProgress(currentProgess); //發(fā)消息，讓主線程刷新文本進(jìn)度 handler.sendEmptyMessage(); //生成臨時(shí)文件保存下載進(jìn)度，用于斷點(diǎn)續(xù)傳，在所有線程現(xiàn)在完畢后刪除臨時(shí)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(dāng)所有線程都下在完了之后，刪除臨時(shí)進(jìn)度文件 FinishedThread++; synchronized (Path) { if (FinishedThread==ThreadCount) { for (int i = ; i < ThreadCount; i++) { File f = new File(Environment.getExternalStorageDirectory(),i+".txt"); f.delete(); } FinishedThread=; } } } } catch (Exception e) { e.printStackTrace(); } } }} |
以上內(nèi)容是小編跟大家分享的PC版與Android手機(jī)版帶斷點(diǎn)續(xù)傳的多線程下載，希望大家喜歡。
