java多线程实现文件下载

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
 
public class DownloadManager implements Runnable {
 // 保存路径
 private String savePath;
 // 总的下载线程数
 private int threadNum;
 // 下载的链接地址
 private String urlFile;
 // 是否下载开始
 private boolean isStarted;
 // 用于监视何时合并文件存放Thread的list
 private List<DownloadThread> downloadList = new ArrayList<DownloadThread>();
 
 public DownloadManager(String savePath, int threadNum, String urlFile) {
 super();
 this.savePath = savePath;
 this.threadNum = threadNum;
 this.urlFile = urlFile;
 }
 
 // 最终调用线程下载。本线程中调用分线程。
 public void action() {
 new Thread(this).start();
 }
 
 public void run() {
 long t1 = System.currentTimeMillis();
 System.out.println(t1);
 // 如果没有下载 ， 就开始 ， 并且将已经下载的变量值设为true
 if (!isStarted) {
 startDownload();
 isStarted = true;
 }
 while (true) {
 // 初始化认为所有线程下载完成，逐个检查
 boolean finish = true;
 // 如果有任何一个没完成，说明下载没完成，不能合并文件
 for (DownloadThread thread : downloadList) {
 if (!thread.isFinish()) {
 finish = false;
 break;
 }
 }
 // 全部下载完成才为真
 if (finish) {
 // 合并文件
 mergeFiles();
 // 跳出循环 ， 下载结束
 break;
 }
 // 休息一会 ， 减少cpu消耗
 try {
 Thread.sleep(1000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 }
 long t2 = System.currentTimeMillis();
 System.out.println(t2);
 System.out.println("下载用时：" + (t2 -t1));
 }
 
 public void startDownload() {
 // 得到每个线程开始值 ， 下载字节数大小
 int[][] posAndLength = getPosAndLength();
 // 根据下载信息创建每个下载线程，并且启动他们。
 for (int i = 0; i < posAndLength.length; i++) {
 int pos = posAndLength[i][0];
 int length = posAndLength[i][1];
 DownloadThread downloadThread = new DownloadThread(i + 1, length,
 pos, savePath, urlFile);
 new Thread(downloadThread).start();
 downloadList.add(downloadThread);
 }
 }
 
 /**
 * 获得文件大小
 * 
 * @return 文件大小
 */
 public long getFileLength() {
 System.out.println("获得文件大小 start......");
 HttpURLConnection conn = null;
 long result = 0;
 try {
 URL url = new URL(urlFile);
 conn = (HttpURLConnection) url.openConnection();
 // 使用Content-Length头信息获得文件大小
 result = Long.parseLong(conn.getHeaderField("Content-Length"));
 } catch (MalformedURLException e) {
 e.printStackTrace();
 } catch (IOException e) {
 e.printStackTrace();
 } finally {
 if (conn != null) {
 conn.disconnect();
 }
 }
 System.out.println("获得文件大小 end......" + result);
 return result;
 }
 
 // 具体细节求出每个线程的开始位置和文件下载大小
 public int[][] getPosAndLength() {
 int[][] result = new int[threadNum][2];
 int fileLength = (int) getFileLength();
 int every = fileLength % threadNum == 0 ? fileLength / threadNum
 : fileLength / threadNum + 1;
 for (int i = 0; i < result.length; i++) {
 int length = <b>本文来源gao@!dai!ma.com搞$$代^@码5网@</b>0;
 if (i != result.length - 1) {
 length = every;
 } else {
 length = fileLength - i * every;
 }
 result[i][0] = i * every;
 result[i][1] = length;
 }
 return result;
 }
 
 // 合并文件
 public void mergeFiles() {
 System.out.println("合并文件 start......");
 OutputStream out = null;
 try {
 out = new FileOutputStream(savePath);
 for (int i = 1; i <= threadNum; i++) {
 InputStream in = new FileInputStream(savePath + i);
 byte[] bytes = new byte[2048];
 int read = 0;
 while ((read = in.read(bytes)) != -1) {
 out.write(bytes, 0, read);
 out.flush();
 }
 if (in != null) {
 in.close();
 new File(savePath + i).delete();
 }
 }
 } catch (Exception e) {
 e.printStackTrace();
 } finally {
 if (out != null) {
 try {
 out.close();
 } catch (IOException e) {
 e.printStackTrace();
 }
 }
 }
 System.out.println("合并文件 end......");
 }
 
 public String getSavePath() {
 return savePath;
 }
 
 public void setSavePath(String savePath) {
 this.savePath = savePath;
 }
 
 public int getThreadNum() {
 return threadNum;
 }
 
 public void setThreadNum(int threadNum) {
 this.threadNum = threadNum;
 }
 
 public String getUrlFile() {
 return urlFile;
 }
 
 public void setUrlFile(String urlFile) {
 this.urlFile = urlFile;
 }
 
 public boolean isStarted() {
 return isStarted;
 }
 
 public void setStarted(boolean isStarted) {
 this.isStarted = isStarted;
 }
 
 public List<DownloadThread> getDownloadList() {
 return downloadList;
 }
 
 public void setDownloadList(List<DownloadThread> downloadList) {
 this.downloadList = downloadList;
 }
}