Java多线程文件下载
一. 多线程下载文件考虑处理步骤：
1. 如何获取文件的长度
2. 合理的创建线程数量，并计算每一个线程下载的长度
3. 如何将多个线程下载的字节写入到文件中
二. 代码实现如下：
package com.bochao.download;
import java.io.File;
import java.net.URL;
import java.net.URLConnection;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
* HTTP多线程下载
*
* @Author DuanCZ
* @Date 2015年9月30日-上午9:28:28
*/
public class HttpMulitThreadDownload {
// 下载文件路径
private String downloadFilePath = null;
// 保存文件路径
private String saveFileDir = "c:\\";
// 默认合理并发线程数
private int threadCount = Runtime.getRuntime().availableProcessors() * 2;
// 新文件名称
private String newFileName = null;
public HttpMulitThreadDownload(int threadCount, String downloadFilePath, String saveFileDir, String newFileName) {
// 用户指定线程数如果小于默认线程数则使用用户指定线程数
if (threadCount < this.threadCount) {
this.threadCount = threadCount;
}
this.downloadFilePath = downloadFilePath;
this.saveFileDir = saveFileDir;
this.newFileName = newFileName;
}
public void MulitThreadDownload() {
// 数据合法性验证
if (null == downloadFilePath || downloadFilePath.isEmpty()) {
throw new RuntimeException("请指定下载路径!");
}
if (null == saveFileDir || saveFileDir.isEmpty()) {
throw new RuntimeException("请指定保存路径!");
}
// 创建保存文件路径如果不存在
File saveFileDirTemp = new File(saveFileDir);
if (!saveFileDirTemp.exists()) {
saveFileDirTemp.mkdirs();
}
// 处理文件名称
if (null == newFileName || newFileName.isEmpty()) {
newFileName = downloadFilePath.substring(downloadFilePath.lastIndexOf("/") + 1, downloadFilePath.length());
}
// 创建固定大小的线程池
ExecutorService threadPool = Executors.newFixedThreadPool(threadCount);
try {
// 根据文件长度计算合理线程数开始
URLConnection urlConnection = new URL(downloadFilePath).openConnection();
// 获取文件长度
int downloadFileLength = urlConnection.getContentLength();
// 计算每个线程负责的文件字节长度
int averageThreadLength = downloadFileLength / threadCount;
int residueThreadLength = downloadFileLength % threadCount;
// 让每一个线程开始工作
int startIndex = 0;
int endIndex = 0;
for (int i = 0; i < threadCount; i++) {
// 计算每一个线程开始和计数索引
startIndex = i * averageThreadLength;
// 如果是最后一个线程，则将剩余的全部下载
if ((i + 1) == threadCount) {
endIndex = (i + 1) * averageThreadLength + residueThreadLength - 1;
}
endIndex = (i + 1) * averageThreadLength - 1;
// 创建下载线程对象
DownloadHandlerThread downloadHandlerThread = new DownloadHandlerThread();
downloadHandlerThread.setDownloadFilePath(downloadFilePath);
downloadHandlerThread.setSaveFilePath(saveFileDir + newFileName);
downloadHandlerThread.setStartIndex(startIndex);
downloadHandlerThread.setEndIndex(endIndex);
threadPool.execute(downloadHandlerThread);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// 关闭线程池
threadPool.shutdown();
}
}
}
package com.bochao.download;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.URL;
import java.net.URLConnection;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
* 下载文件处理线程
*
* @Author DuanCZ
* @Date 2015年9月30日-上午11:38:42
*/
public class DownloadHandlerThread implements Runnable {
// 待下载的HTTP文件路径
private String downloadFilePath = null;
// 下载保存文件路径
private String saveFilePath = null;
// 文件随机写入开始索引
private int startIndex = 0;
// 文件随机写入结束索引
private int endIndex = 0;
@Override
public void run() {
System.out.println("线程名称[" + Thread.currentThread().getName() + "]于时间["
+ new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "]开始下载....");
// 文件输入流对象
InputStream fileInputStream = null;
// 随机访问文件
RandomAccessFile randomAccessFile = null;
// ------------------------------------------------------------------------------
// 获取随机文件流开始
// 获取一个URL打开链接对象
URLConnection urlConnection = null;
try {
urlConnection = new URL(downloadFilePath).openConnection();
} catch (IOException e1) {
e1.printStackTrace();
}
// 设置该链接允许和用户交互
urlConnection.setAllowUserInteraction(true);
// 设置请求属性字节范围
urlConnection.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex + "");
try {
// 获取指定的文件流
fileInputStream = urlConnection.getInputStream();
} catch (IOException e) {
e.printStackTrace();
}
// ------------------------------------------------------------------------------获取随机文件流结束
// ------------------------------------------------------------------------
// 写文件流到指定的文件开始
try {
// 创建文件随机访问对象
randomAccessFile = new RandomAccessFile(saveFilePath, "rw");
// 将文件写入位置移动到其实点
randomAccessFile.seek(startIndex);
// 写入文件
int bytes = 0;
byte[] buffer = new byte[100 * 1024];
while ((bytes = fileInputStream.read(buffer, 0, buffer.length)) != -1) {
randomAccessFile.write(buffer, 0, bytes);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (null != randomAccessFile) {
randomAccessFile.close();
}
if (null != fileInputStream) {
fileInputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
// ------------------------------------------------------------------------写文件流到指定的文件结束
System.out.println("线程名称[" + Thread.currentThread().getName() + "]于时间["
+ new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()) + "]下载完成！");
}
public String getDownloadFilePath() {
return downloadFilePath;
}
public void setDownloadFilePath(String downloadFilePath) {
this.downloadFilePath = downloadFilePath;
}
public String getSaveFilePath() {
return saveFilePath;
}
public void setSaveFilePath(String saveFilePath) {
this.saveFilePath = saveFilePath;
}
public int getStartIndex() {
return startIndex;
}
public void setStartIndex(int startIndex) {
this.startIndex = startIndex;
}
public int getEndIndex() {
return endIndex;
}
public void setEndIndex(int endIndex) {
this.endIndex = endIndex;
}
}
测试：
package com.bochao.download;
public class TestDownload {
public static void main(String[] args) {
String downloadFilePath = "http://localhost:81/mulitThreadDownload/file/PowerDesigner165_Evaluation.1428562995.exe";
String saveFileDir= "f:\\Download\\";
HttpMulitThreadDownload httpMulitThreadDownload = new HttpMulitThreadDownload(2, downloadFilePath, saveFileDir, "powerdesigner.exe");
httpMulitThreadDownload.MulitThreadDownload();
}
}
输出结果：
线程名称[pool-1-thread-1]于时间[2015-08-30 16:09:49]开始下载....
线程名称[pool-1-thread-2]于时间[2015-08-30 16:09:49]开始下载....
线程名称[pool-1-thread-2]于时间[2015-09-30 16:09:01]下载完成！
线程名称[pool-1-thread-1]于时间[2015-09-30 16:09:23]下载完成！
