java多线程实现文件下载

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 downloadList = new ArrayList();

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 getDownloadList() {

return downloadList;

}

public void setDownloadList(List 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 =http:// 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;

}

cQcbvWebbpublic 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！

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