以前看過一個前輩寫的斷點續傳的文章,記得當時沒看懂,就扔那了。昨天翻了出來,自己也仿照寫了一個,不過感覺沒人家寫的好,有點亂,希望大家能來批評、指正,給點意見!
功能很簡單,就是啓動多個線程分別從給定的地址下載數據,用RandomAccessFile寫到目標文件。實現思路是:
1、獲得連接的長度(即要下載的文件大小),除以設定的線程數,即得到每個線程要下載的大小。
2、記錄臨時文件,文件中記錄每個線程的編號(id),該線程要下載的起始位置、終止位置和當前位置(當前位置在首次下載時與起始位置相同)。
3、啓動具體執行下載任務的線程,並等待其結束。
4、下載完成,刪除臨時文件。
代碼如下:
主線程及測試的main方法
- package com.why.download.test;
- import java.io.DataOutputStream;
- import java.io.File;
- import java.io.FileOutputStream;
- import java.io.IOException;
- import java.math.BigDecimal;
- import java.net.HttpURLConnection;
- import java.net.URL;
- import java.net.URLConnection;
- import java.util.UUID;
- import java.util.concurrent.CountDownLatch;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- /**
- *
- * @author why
- *
- */
- public class DownLoad {
- //文件目錄、文件名
- public String fileDir = "E:/MyDownLoad";
- public String fileName;
- //超時重連時間
- public long reconnectTime = 5;
- //線程數
- private int poolSize = 5;
- //每個線程的緩衝區大小
- public int bufferSize = 1024;
- //url地址
- private String urlLocation = null;
- public DownLoad(){}
- public DownLoad(String url){
- this.urlLocation = url;
- }
- public void downLoad(){
- if(this.urlLocation == null || "".equals(this.urlLocation))return;
- downLoad(this.urlLocation);
- }
- public void downLoad(String urlLocation){
- File file = null;
- File tempFile = null;
- CountDownLatch latch;
- URL url = null;
- ExecutorService pool = Executors.newCachedThreadPool();
- long contentLength = 0;
- long threadLength = 0;
- try {
- //如果未指定名稱,則從url中獲得下載的文件格式與名字
- if(fileName == null || "".equals(fileName)){
- this.fileName = urlLocation.substring(urlLocation.lastIndexOf("/") + 1,
- urlLocation.lastIndexOf("?") > 0 ? urlLocation.lastIndexOf("?")
- : urlLocation.length());
- if ("".equalsIgnoreCase(this.fileName)) {
- this.fileName = UUID.randomUUID().toString();
- }
- }
- new File(fileDir).mkdirs();
- file = new File(fileDir + File.separator + fileName);
- tempFile = new File(fileDir + File.separator + fileName + "_temp");
- url = new URL(urlLocation);
- HttpURLConnection conn = (HttpURLConnection) url.openConnection();
- setHeader(conn);
- //得到content的長度
- contentLength = conn.getContentLength();
- System.out.println("total length=" + contentLength);
- //把context分爲poolSize段,計算每段的長度。
- // threadLength = contentLength / this.poolSize;
- BigDecimal b1 = new BigDecimal(Double.toString(contentLength));
- BigDecimal b2 = new BigDecimal(Double.toString(this.poolSize));
- threadLength = b1.divide(b2, 0, BigDecimal.ROUND_HALF_UP).longValue();
- if(file.exists() && tempFile.exists()){
- //如果文件已存在,根據臨時文件中記載的線程數量,繼續上次的任務
- latch = new CountDownLatch((int)tempFile.length()/28);
- for(int i=0;i<tempFile.length()/28;i++){
- pool.submit(new DownLoadTask(file, tempFile, url, i+1,latch,reconnectTime,bufferSize));
- }
- }else{
- //如果下載的目標文件不存在,則創建新文件
- latch = new CountDownLatch(poolSize);
- file.createNewFile();
- tempFile.createNewFile();
- DataOutputStream os = new DataOutputStream(new FileOutputStream(tempFile));
- for(int i=0;i<this.poolSize;i++){
- os.writeInt(i+1);
- os.writeLong(i*threadLength);
- if(i==this.poolSize-1){//最後一個線程的結束位置應爲文件末端
- os.writeLong(contentLength);
- }else{
- os.writeLong((i+1)*threadLength);
- }
- os.writeLong(i*threadLength);
- pool.submit(new DownLoadTask(file, tempFile, url, i+1,latch,reconnectTime,bufferSize));
- }
- os.close();
- }
- //等待下載任務完成
- latch.await();
- //刪除臨時文件
- tempFile.delete();
- } catch (IOException e) {
- e.printStackTrace();
- } catch (InterruptedException e) {
- e.printStackTrace();
- } finally{
- pool.shutdown();
- }
- }
- private void setHeader(URLConnection conn) {
- conn.setRequestProperty("User-Agent",
- "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3");
- conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");
- conn.setRequestProperty("Accept-Encoding", "aa");
- conn.setRequestProperty("Accept-Charset","ISO-8859-1,utf-8;q=0.7,*;q=0.7");
- conn.setRequestProperty("Keep-Alive", "300");
- conn.setRequestProperty("Connection", "keep-alive");
- conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT");
- conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");
- conn.setRequestProperty("Cache-Control", "max-age=0");
- conn.setRequestProperty("Referer","http://www.skycn.com/soft/14857.html");
- }
- public String getFileDir() {
- return fileDir;
- }
- public void setFileDir(String fileDir) {
- this.fileDir = fileDir;
- }
- public String getFileName() {
- return fileName;
- }
- public void setFileName(String fileName) {
- this.fileName = fileName;
- }
- public long getReconnectTime() {
- return reconnectTime;
- }
- public void setReconnectTime(long reconnectTime) {
- this.reconnectTime = reconnectTime;
- }
- public int getPoolSize() {
- return poolSize;
- }
- public void setPoolSize(int poolSize) {
- this.poolSize = poolSize;
- }
- public int getBufferSize() {
- return bufferSize;
- }
- public void setBufferSize(int bufferSize) {
- this.bufferSize = bufferSize;
- }
- /**
- * @param args
- */
- public static void main(String[] args) {
- DownLoad dl = new DownLoad();
- dl.setFileDir("E:/MyDownLoad/music/");
- dl.setFileName("大笑江湖.mp3");
- dl.setPoolSize(20);
- long beginTime = System.currentTimeMillis();
- dl.downLoad("http://mh.163k.com/UploadFile/video/2010/12-13/201012131213448942190.mp3");
- long endTime = System.currentTimeMillis();
- BigDecimal b1 = new BigDecimal(endTime - beginTime);
- BigDecimal b2 = new BigDecimal(1000);
- double cost = b1.divide(b2, 2, BigDecimal.ROUND_HALF_UP).doubleValue();
- System.out.println("Time cost:" + cost + "s");
- }
- }
執行下載任務的線程:
- package com.why.download.test;
- import java.io.File;
- import java.io.FileNotFoundException;
- import java.io.IOException;
- import java.io.InputStream;
- import java.io.RandomAccessFile;
- import java.net.HttpURLConnection;
- import java.net.URL;
- import java.net.URLConnection;
- import java.util.concurrent.Callable;
- import java.util.concurrent.CountDownLatch;
- import java.util.concurrent.TimeUnit;
- /**
- *
- * @author why
- *
- */
- public class DownLoadTask implements Callable<String>{
- //超時重連時間
- private long reconnectTime = 5;
- //緩衝區大小
- private int bufferSize = 1024;
- private CountDownLatch latch;
- private RandomAccessFile file = null;
- private RandomAccessFile tempFile = null;
- private URL url = null;
- private int id;
- private long startPosition;
- private long endPosition;
- private long currentPosition ;
- public DownLoadTask(File file,File tempFile,URL url,int id,CountDownLatch latch,long reconnectTime,int bufferSize){
- try {
- this.file = new RandomAccessFile(file, "rw");
- this.tempFile = new RandomAccessFile(tempFile, "rw");
- } catch (FileNotFoundException e) {
- e.printStackTrace();
- }
- this.url = url;
- this.id = id;
- this.latch = latch;
- }
- public String call(){
- try {
- tempFile.seek((id-1)*28);
- tempFile.readInt();
- this.startPosition = tempFile.readLong();
- this.endPosition = tempFile.readLong();
- this.currentPosition = tempFile.readLong();
- } catch (IOException e) {
- e.printStackTrace();
- }
- System.out.println("Thread " + id + " begin!");
- HttpURLConnection conn = null;
- InputStream inputStream = null;
- while(true){
- try {
- tempFile.seek(id*28 - 8);
- // 打開URLConnection
- conn = (HttpURLConnection) this.url.openConnection();
- setHeader(conn);
- // 設置連接超時時間爲10000ms
- conn.setConnectTimeout(10000);
- // 設置讀取數據超時時間爲10000ms
- conn.setReadTimeout(10000);
- if (currentPosition < endPosition) {
- // 設置下載數據的起止區間
- conn.setRequestProperty("Range", "bytes=" + currentPosition + "-" + endPosition);
- System.out.println("Thread " + id + " startPosition=" + startPosition
- + ",endPosition=" + endPosition + ",currentPosition=" + currentPosition);
- file.seek(currentPosition);
- // 判斷http status是否爲HTTP/1.1 206 Partial Content或者200 OK
- // 如果不是以上兩種狀態,把status改爲STATUS_HTTPSTATUS_ERROR
- if (conn.getResponseCode() != HttpURLConnection.HTTP_OK
- && conn.getResponseCode() != HttpURLConnection.HTTP_PARTIAL) {
- System.out.println("Thread " + id + ": code = " + conn.getResponseCode() + ", status = " + conn.getResponseMessage());
- file.close();
- conn.disconnect();
- System.out.println("Thread " + id + " finished.");
- break;
- }
- inputStream = conn.getInputStream();
- int len = 0;
- byte[] b = new byte[bufferSize];
- while ((len = inputStream.read(b)) != -1) {
- file.write(b, 0, len);
- currentPosition += len;
- // set tempFile now position
- tempFile.seek(id*28 - 8);
- tempFile.writeLong(currentPosition);
- }
- file.close();
- tempFile.close();
- inputStream.close();
- conn.disconnect();
- }
- System.out.println("Thread " + id + " finished.");
- break;
- } catch (IOException e) {
- try {
- TimeUnit.SECONDS.sleep(getReconnectTime());
- } catch (InterruptedException e1) {
- e1.printStackTrace();
- }
- continue;
- }
- }
- latch.countDown();
- return "finish";
- }
- private void setHeader(URLConnection conn) {
- conn.setRequestProperty("User-Agent",
- "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3");
- conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");
- conn.setRequestProperty("Accept-Encoding", "aa");
- conn.setRequestProperty("Accept-Charset","ISO-8859-1,utf-8;q=0.7,*;q=0.7");
- conn.setRequestProperty("Keep-Alive", "300");
- conn.setRequestProperty("Connection", "keep-alive");
- conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT");
- conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");
- conn.setRequestProperty("Cache-Control", "max-age=0");
- conn.setRequestProperty("Referer","http://www.skycn.com/soft/14857.html");
- }
- public long getReconnectTime() {
- return reconnectTime;
- }
- public void setReconnectTime(long reconnectTime) {
- this.reconnectTime = reconnectTime;
- }
- public int getBufferSize() {
- return bufferSize;
- }
- public void setBufferSize(int bufferSize) {
- this.bufferSize = bufferSize;
- }
- }
最近一直在測試,寫文檔,好久沒敲代碼了。手有點癢,寫着玩的,代碼寫的不是很工整,純屬娛樂!
轉載自:http://wuhongyu.iteye.com/blog/869109