java多线程实现文件下载

本文实例为大家分享了java多线程实现文件下载的具体代码，供大家参考，具体内容如下

1、DownloadManager类

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 = 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;
 }
}

 2、DownloadThread类

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
 
public class DownloadThread implements Runnable {
 // 当前第几个线程 ， 用于给下载文件起名 file1 file2 file3 ...
 private int whichThread;
 // 监听单一线程下载是否完成
 private boolean isFinish;
 // 本线程要下载的文件字节数
 private int length;
 // 本线程向服务器发送请求时输入流的首位置
 private int startPosition;
 // 保存的路径
 private String savePath;
 // 要下载的文件 ， 用于创建连接
 private String url;
 
 public void run() {
 HttpURLConnection conn = null;
 InputStream in = null;
 OutputStream out = null;
 try {
 System.out.println("正在执行的线程：" + whichThread);
 URL fileUrl = new URL(url);
 // 与服务器创建连接
 conn = (HttpURLConnection) fileUrl.openConnection();
 // 下载使用get请求
 conn.setRequestMethod("GET");
 // 告诉服务器 ， 我是火狐 ， 不要不让我下载。
 conn.setRequestProperty(
 "User-Agent",
 "Firefox Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.1.3) Gecko/20090824 Firefox/3.5.3");
 // 这里是设置文件输入流的首位置
 conn.setRequestProperty("Range", "bytes=" + startPosition + "-");
 // 与服务器创建连接
 conn.connect();
 // 获得输入流
 in = conn.getInputStream();
 // 在硬盘上创建file1 , file2 , ...这样的文件 ， 准备往里面写东西
 out = new FileOutputStream(savePath + whichThread);
 // 用于写入的字节数组
 byte[] bytes = new byte[4096];
 // 一共下载了多少字节
 int count = 0;
 // 单次读取的字节数
 int read = 0;
 while ((read = in.read(bytes)) != -1) {
 // 检查一下是不是下载到了本线程需要的长度
 if (length - count < bytes.length) {
 // 比如说本线程还需要900字节，但是已经读取1000
 // 字节，则用要本线程总下载长度减去
 // 已经下载的长度
 read = length - count;
 }
 // 将准确的字节写入输出流
 out.write(bytes, 0, read);
 // 已经下载的字节数加上本次循环字节数
 count = count + read;
 // 如果下载字节达到本线程所需要字节数，消除循环，
 // 停止下载
 if (count == length) {
 break;
 }
 }
 // 将监视变量设置为true
 isFinish = true;
 } catch (Exception e) {
 e.printStackTrace();
 } finally {
 // 最后进行输入、输出、连接的关闭
 if (in != null) {
 try {
 in.close();
 } catch (IOException e) {
 e.printStackTrace();
 }
 }
 if (out != null) {
 try {
 out.close();
 } catch (IOException e) {
 e.printStackTrace();
 }
 }
 if (conn != null) {
 conn.disconnect();
 }
 }
 }
 
 public int getStartPosition() {
 return startPosition;
 }
 
 public void setStartPosition(int startPosition) {
 this.startPosition = startPosition;
 }
 
 public String getUrl() {
 return url;
 }
 
 public void setUrl(String url) {
 this.url = url;
 }
 
 public int getWhichThread() {
 return whichThread;
 }
 
 public void setWhichThread(int whichThread) {
 this.whichThread = whichThread;
 }
 
 public int getLength() {
 return length;
 }
 
 public void setLength(int length) {
 this.length = length;
 }
 
 public String getSavePath() {
 return savePath;
 }
 
 public void setSavePath(String savePath) {
 this.savePath = savePath;
 }
 
 public DownloadThread(int whichThread, int length, int startPosition,
 String savePath, String url) {
 super();
 this.whichThread = whichThread;
 this.length = length;
 this.startPosition = startPosition;
 this.savePath = savePath;
 this.url = url;
 }
 
 public DownloadThread() {
 super();
 }
 
 public boolean isFinish() {
 return isFinish;
 }
 
 public void setFinish(boolean isFinish) {
 this.isFinish = isFinish;
 }
}

3、TestDownload测试类

public class TestDownload {
 
 public static void main(String[] args) {
 DownloadManager downloadManager = new DownloadManager("d:/upload/09018417.zip" , 5 , "http://10.1.2.65:8080/cetvossFront/09018417.zip");
 downloadManager.action();
 }
}

代码已经测试可以运行！

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持小牛知识库。