java多线程下载实例详解

HttpURLConnection.getContentLength();RandomAccessFile file = new RandomAccessFile("youdao.exe","rw");file.setLength(filesize);//设置本地文件的长度

RandomAccessFile threadfile = new RandomAccessFile("<span style="font-family: Arial, Helvetica, sans-serif;">youdao.exe</span><span style="font-family: Arial, Helvetica, sans-serif;"> ","rw");</span>threadfile.seek(2097152);//从文件的什么位置开始写入数据

package www.csdn.net.down;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;public class DownLoadTest { public File file; public RandomAccessFile accessFile; // 线程的数量 public static int threadNum = 3; // 每个线程负责下载的大小 int blockSize; // 创建访问的路径 public String path = "http://localhost:8080/doudou/youdao.exe"; public static int threadCount;// 数量 public void testDown() {  try {   // 创建出URL对象   URL url = new URL(path);   // 创建出 HttpURLConnection对象   HttpURLConnection httpURLConnection = (HttpURLConnection) url     .openConnection();   // 设置 发请求发送的方式   httpURLConnection.setRequestMethod("GET");   // 设置请求是否超时时间   httpURLConnection.setConnectTimeout(5000);   // 设置   httpURLConnection     .setRequestProperty("User-Agent",       " Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0)");   // 是否响应成功   if (httpURLConnection.getResponseCode() == 200) {    // 获取文件的大小    int size = httpURLConnection.getContentLength();    System.out.println("文件的大小" + size);    // 创建文件    file = new File("youdao.exe");    accessFile = new RandomAccessFile(file, "rwd");    // 设置文件的大小    accessFile.setLength(size);    // 每个线程下载的大小    blockSize = size / threadNum;    // 开三个线程 操作此文件    for (int i = 1; i <= threadNum; i++) {     // 1 2 3     // 计算出每个线程开始的位置     int startSize = (i - 1) * blockSize;     // 结束位置     int endSize = (i) * blockSize;     // 当线程是最后一个线程的时候     if (i == threadNum) {      // 判断文件的大小是否大于计算出来的结束位置      if (size > endSize) {       // 结束位置 等于 文件的大小       endSize = size;      }     }     // 为每个线程创建一个随机的读取     RandomAccessFile threadAccessFile = new RandomAccessFile(       file, "rwd");     new Thread(new DownLoadThread(i, threadAccessFile,       startSize, endSize, path)).start();    }   }  } catch (MalformedURLException e) {   // TODO Auto-generated catch block   e.printStackTrace();  } catch (IOException e) {   // TODO Auto-generated catch block   e.printStackTrace();  } } public static void main(String[] args) {  DownLoadTest downLoadTest = new DownLoadTest();  // 调用下载方法  downLoadTest.testDown(); }}class DownLoadThread implements Runnable { // 下载文件的封装 public RandomAccessFile accessFile; // 每个线程 都拥有一个accessFile的文件对象 线程1 线程2 线程3 // 线程下载文件的起始位置 public int startSize; public int endSize; // 文件下载的path路径 public String path; public int threadId; // 线程的标识 public DownLoadThread(int threadId, RandomAccessFile accessFile,   int startSize, int endSize, String path) {  this.threadId = threadId;  this.accessFile = accessFile;  this.startSize = startSize;  this.endSize = endSize;  this.path = path; } @Override public void run() {  // 执行run方法  try {   // 创建文件   File threadFile = new File(threadId + ".txt");   if (threadFile.exists()) {    // 读取该文件的内容    // 创建文件的输入流对象    FileInputStream fis = new FileInputStream(threadFile);    // 采用工具类读取    byte data[] = StreamTools.isToData(fis);    // 转化成字符串    String threadLen = new String(data);    if ((threadLen != null) && (!"".equals(threadLen))) {     startSize = Integer.valueOf(threadLen);     // 解决 416bug的错误     if (startSize > endSize) {      startSize = endSize - 1;     }    }   }   // 创建URL对象   URL url = new URL(path);   // 创建HttpURLConnection对象   HttpURLConnection httpURLConnection = (HttpURLConnection) url     .openConnection();   // 设置请求的头   httpURLConnection.setRequestMethod("GET");   // 设置请求是否超时时间   httpURLConnection.setConnectTimeout(5000);   // 设置   httpURLConnection     .setRequestProperty("User-Agent",       " Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0)");   // 关键的设置   httpURLConnection.setRequestProperty("Range", "bytes=" + startSize     + "-" + endSize);   // 输出当前线程   System.out.println("当前线程" + threadId + " 下载开始位置:" + startSize     + " 下载结束位置:" + endSize);   // 响应成功   // 设置随机读取文件的 开始位置   accessFile.seek(startSize);   // 获取相应流对象   InputStream is = httpURLConnection.getInputStream();   // 创建输出流对象   byte buffer[] = new byte[1024];   int len = 0;   int threadTotal = 0;// 每个线程下载后保存记录 /   while ((len = is.read(buffer)) != -1) {    accessFile.write(buffer, 0, len);    threadTotal += len;// 记录你写入的长度 //xml文件    // 通过文件记录文件下载的长度    FileOutputStream fos = new FileOutputStream(threadFile);    fos.write((threadTotal + "").getBytes());    fos.flush();    fos.close();   }   accessFile.close();   is.close();   System.out.println(threadId + "线程执行完毕");   //线程操作   synchronized (DownLoadTest.class) {    DownLoadTest.threadCount++;    if (DownLoadTest.threadCount >= DownLoadTest.threadNum) {     for(int i=1;i<=DownLoadTest.threadNum;i++){      File file = new File(i+".txt");      if(file.exists()){       file.delete();      }     }    }   }  } catch (MalformedURLException e) {   // TODO Auto-generated catch block   e.printStackTrace();  } catch (IOException e) {   // TODO Auto-generated catch block   e.printStackTrace();  } }}

package www.csdn.net.down;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.InputStream;public class StreamTools { public static byte[] isToData(InputStream is) throws IOException{  // 字节输出流  ByteArrayOutputStream bops = new ByteArrayOutputStream();  // 读取数据的缓存区  byte buffer[] = new byte[1024];  // 读取长度的记录  int len = 0;  // 循环读取  while ((len = is.read(buffer)) != -1) {   bops.write(buffer, 0, len);  }  // 把读取的内容转换成byte数组  byte data[] = bops.toByteArray();  bops.flush();  bops.close();  is.close();  return data; }}