java多线程断点续传

 在android下面的断点续传和java下面没有太大的冲突，就是在配置文件里面加上一些特定的访问权限就可以了如下式在AndroidManifest.xml加入的权限 <!--  访问internet权限 -->       <uses-permission android:name="android.permission.INTERNET" />       <!--  在SDCard中创建与删除文件权限-->       <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />       <!--  往SDCard写入数据权限-->       <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />这个准备工作做好了就可以直接编码了第一步创建multiThreaddownload.java package com.cn.download; import java.io.File;import java.io.FileInputStream;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.URL;import java.net.URLConnection; import com.cn.coocaa.download.FileDownloadThread; public class MultiThreadDownload extends Thread {        //定义的一些常量变量，看名字就知道什么意思了private static final int BUFFER_SIZE = 1024;private int blockSize;private int threadNum = 5;private int fileSize;private int downloadedSize;String urlStr, threadNo, fileName;private String savePath;private int downloadPercent = 0 , downloadSpeed = 0, usedTime=0;private long startTime,curTime;privateboolean completed = false;        //用URL,保存路径,保存名称来构造。public MultiThreadDownload(String URL, String savePath, String fileName) {this.urlStr = URL;this.savePath = savePath;this.fileName = fileName;} @Overridepublic void run() {FileDownloadThread[] fds = new FileDownloadThread[threadNum];try {URL url = new URL(urlStr);URLConnection conn = url.openConnection();fileSize = conn.getContentLength();blockSize = fileSize / threadNum;File file[] = new File[threadNum];                        //根据默认的线程数，或者自己修改设置的线程数来分块，创建分块后的文件块for (int i = 0; i < threadNum; i++) {file[i] = new File(savePath + fileName + ".part"+ String.valueOf(i));                                //将分块的文件交给每个线程处理，最后一块应该大于等于平均块，因为可能有余数FileDownloadThread fdt = new FileDownloadThread(url, file[i], i* blockSize, (i + 1) != threadNum ? ((i + 1)* blockSize - 1) : fileSize);fdt.setName("Thread" + i);fdt.start();fds[i] = fdt;}startTime = System.currentTimeMillis();                        //获取起始下载的时间，用次来计算速度。boolean finished = false;while (!finished) {downloadedSize = 0;finished = true;for (int i = 0; i < fds.length; i++) {downloadedSize += fds[i].getDownloadSize();if (!fds[i].isFinished()) {finished = false;}}                                //计算下载的百分比downloadPercent = (downloadedSize*100)/fileSize;                                //获取当前时间，计算平均下载速度curTime = System.currentTimeMillis();usedTime =(int)((curTime-startTime)/1000);if(usedTime==0)usedTime =1;downloadSpeed = (downloadedSize/usedTime)/1024;sleep(1000);}                       //这个是分块下载完成的标志completed = true;                        //进行模块整合RandomAccessFile raf = new RandomAccessFile(savePath + fileName,"rw");byte[] tempbytes = new byte[BUFFER_SIZE];InputStream in = null;int byteread = 0;for (int i = 0; i < threadNum; i++) {in = new FileInputStream(file[i]);while ((byteread = in.read(tempbytes)) != -1){raf.write(tempbytes, 0, byteread);}                                //每次整合完一块就删除一块。in.close();file[i].delete();}raf.close(); } catch (Exception e) {// TODO: handle exception}}       //获取下载百分比public int getDownloadPercent(){return this.downloadPercent;}       //获取下载速度public int getDownloadSpeed(){return this.downloadSpeed;}       //修改默认线程数public void setThreadNum(int threadNum){this.threadNum = threadNum;}        //分块下载完成的标志public boolean isCompleted(){return this.completed;}}第二步 创建filedownloadthread.javapackage com.cn.download; import java.io.BufferedInputStream;import java.io.File;import java.io.IOException;import java.io.RandomAccessFile;import java.net.URL;import java.net.URLConnection; public class FileDownloadThread extends Thread {private static final int BUFFER_SIZE = 1024;private URL url;private File file;private int startPosition;private int endPosition;private int curPosition;private boolean finished = false;private int downloadSize = 0;       //分块构造函数public FileDownloadThread(URL url, File file, int startPosition,int endPosition) {this.url = url;this.file = file;this.startPosition = startPosition;this.curPosition = startPosition;this.endPosition = endPosition;} public void run() {  BufferedInputStream bis = null;RandomAccessFile fos = null;byte[] buf = new byte[BUFFER_SIZE];URLConnection con = null;try {                       //打开URL连接con = url.openConnection();con.setAllowUserInteraction(true);                       //判断是否该文件存在，如果存在且下载完成，直接返回。if ((file.length() + startPosition) == endPosition) {this.finished = true;}                        //文件未下载完成，获取到当前指针位置，继续下载。                         else {con.setRequestProperty("Range", "bytes="+ (startPosition + file.length()) + "-" + endPosition);fos = new RandomAccessFile(file, "rw");fos.seek(file.length());bis = new BufferedInputStream(con.getInputStream());while (curPosition < endPosition) {int len = bis.read(buf, 0, BUFFER_SIZE);if (len == -1) {break;}fos.write(buf, 0, len);curPosition = curPosition + len;if (curPosition > endPosition) {downloadSize += len - (curPosition - endPosition) + 1;} else {downloadSize += len;}}this.finished = true;bis.close();fos.close();}} catch (IOException e) {System.out.println(getName() + " Error:" + e.getMessage());}} public boolean isFinished() {return finished;} public int getDownloadSize() {return downloadSize;}}上述两个文件就完成了多线程断点续传。   无需使用任何配置文件或者数据库，就可以接上次的断点进行续传操作。 原理流程：         1、获取文件大小         2、将文件按照所设定的线程数进行分块请求。         3、检查是否存在断点情况，如果有断点情况则进行断点查找，然后再请求。         4、分块下载。         5、下载完成后文件整合，将分块文件删除掉。         6、好了，你需要下载的文件就可以完成了。  总之了，在这里也是一种实现无需配置文件的方式吧，我提供的只是一个外部调用包，所以这个配置文件或者数据库记录的东西有很大的局限性，所以就切割了， 如果有什么更好的想法，希望能相互交流交流。 转载请注明：http://alloxa.blog.51cto.com/
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