title: 使用Java下载大文件
date: 2017-09-04 04:51:12
tags: [Java]
---
主要思路是将大文件分解成若干个小文件进行下载.
本功能由两个类实现:DownLoadManager和DownloadThreadTask实现. 其中DownLoadManager类主要负责下载任务的初始化和调度, DownloadThreadTask主要负责处理下载任务.
用到的主要工具类有
org.apache.http.impl.client.CloseableHttpClient 模拟httpClient客户端发送http请求，可以控制到请求文件的字节位置。
BufferedInputStream都熟悉，用它接受请求来的流信息缓存。
RandomAccessFile文件随机类，可以向文件写入指定位置的流信息。
代码如下:
DownLoadManager
package util;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* 文件下载管理类
*/
public class DownLoadManager{
private static final Logger LOGGER = LoggerFactory.getLogger(DownLoadManager.class);
/**
* 每个线程下载的字节数
*/
private long unitSize = 1000 * 1024;
private ExecutorService taskExecutor = Executors.newFixedThreadPool(10);
private CloseableHttpClient httpClient;
public DownLoadManager() {
PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
cm.setMaxTotal(100);
httpClient = HttpClients.custom().setConnectionManager(cm).build();
}
public static void main(String[] args) throws IOException {
new DownLoadManager().doDownload();
}
/**
* 启动多个线程下载文件
*/
public void doDownload() throws IOException {
//要下载的url
String remoteFileUrl = "http://cn-sdjn-cu-v-04.acgvideo.com/vg4/e/60/21029304-1.mp4?expires=1504513500&platform=pc&ssig=4-pYfuQHUKppz3XGrw6Hnw&oi=1032322900&nfa=T7l/1XWXSxfil4KoioiGpQ==&dynamic=1&hfa=2073962963&hfb=Yjk5ZmZjM2M1YzY4ZjAwYTMzMTIzYmIyNWY4ODJkNWI=";
String localPath = "E://temp//";
String fileName = new URL(remoteFileUrl).getFile();
System.out.println("远程文件名称：" + fileName);
fileName = fileName.substring(fileName.lastIndexOf("/") + 1, fileName.length()).replace("%20", " ");
System.out.println("本地文件名称：" + fileName);
long fileSize = this.getRemoteFileSize(remoteFileUrl);
this.createFile(localPath + System.currentTimeMillis() + fileName, fileSize);
Long threadCount = (fileSize / unitSize) + (fileSize % unitSize != 0 ? 1 : 0);
long offset = 0;
CountDownLatch end = new CountDownLatch(threadCount.intValue());
if (fileSize <= unitSize) {// 如果远程文件尺寸小于等于unitSize
DownloadThreadTask downloadThread = new DownloadThreadTask(remoteFileUrl, localPath + fileName, offset, fileSize, end, httpClient);
taskExecutor.execute(downloadThread);
} else {// 如果远程文件尺寸大于unitSize
for (int i = 1; i < threadCount; i++) {
DownloadThreadTask downloadThread = new DownloadThreadTask(remoteFileUrl, localPath + fileName, offset, unitSize, end, httpClient);
taskExecutor.execute(downloadThread);
offset = offset + unitSize;
}
if (fileSize % unitSize != 0) {// 如果不能整除，则需要再创建一个线程下载剩余字节
DownloadThreadTask downloadThread = new DownloadThreadTask(remoteFileUrl, localPath + fileName, offset, fileSize - unitSize * (threadCount - 1), end, httpClient);
taskExecutor.execute(downloadThread);
}
}
try {
end.await();
} catch (InterruptedException e) {
LOGGER.error("DownLoadManager exception msg:{}", ExceptionUtils.getFullStackTrace(e));
e.printStackTrace();
}
taskExecutor.shutdown();
LOGGER.debug("下载完成！{} ", localPath + fileName);
}
/**
* 获取远程文件尺寸
*/
private long getRemoteFileSize(String remoteFileUrl) throws IOException {
long fileSize = 0;
HttpURLConnection httpConnection = (HttpURLConnection) new URL(remoteFileUrl).openConnection();
//使用HEAD方法
httpConnection.setRequestMethod("HEAD");
int responseCode = httpConnection.getResponseCode();
if (responseCode >= 400) {
LOGGER.debug("Web服务器响应错误!");
return 0;
}
String sHeader;
for (int i = 1;; i++) {
sHeader = httpConnection.getHeaderFieldKey(i);
if (sHeader != null && sHeader.equals("Content-Length")) {
System.out.println("文件大小ContentLength:" + httpConnection.getContentLength());
fileSize = Long.parseLong(httpConnection.getHeaderField(sHeader));
break;
}
}
return fileSize;
}
/**
* 创建指定大小的文件
*/
private void createFile(String fileName, long fileSize) throws IOException {
File newFile = new File(fileName);
RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
raf.setLength(fileSize);
raf.close();
}
}DownloadThreadTask
package util;
import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.CountDownLatch;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* 负责文件下载的类
*/
public class DownloadThreadTask implements Runnable {
private static final Logger LOGGER = LoggerFactory.getLogger(DownloadThreadTask.class);
/**
* 待下载的文件
*/
private String url = null;
/**
* 本地文件名
*/
private String fileName = null;
/**
* 偏移量
*/
private long offset = 0;
/**
* 分配给本线程的下载字节数
*/
private long length = 0;
private CountDownLatch end;
private CloseableHttpClient httpClient;
private HttpContext context;
/**
* @param url
* 下载文件地址
* @param fileName
* 另存文件名
* @param offset
* 本线程下载偏移量
* @param length
* 本线程下载长度
*/
public DownloadThreadTask(String url, String file, long offset, long length, CountDownLatch end, CloseableHttpClient httpClient) {
this.url = url;
this.fileName = file;
this.offset = offset;
this.length = length;
this.end = end;
this.httpClient = httpClient;
this.context = new BasicHttpContext();
LOGGER.debug("偏移量=" + offset + ";字节数=" + length);
}
public void run() {
try {
HttpGet httpGet = new HttpGet(this.url);
httpGet.addHeader("Range", "bytes=" + this.offset + "-" + (this.offset + this.length - 1));
httpGet.addHeader("Referer", "http://api.bilibili.com");
CloseableHttpResponse response = httpClient.execute(httpGet, context);
BufferedInputStream bis = new BufferedInputStream(response.getEntity().getContent());
byte[] buff = new byte[1024];
int bytesRead;
File newFile = new File(fileName);
RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
while ((bytesRead = bis.read(buff, 0, buff.length)) != -1) {
raf.seek(this.offset);
raf.write(buff, 0, bytesRead);
this.offset = this.offset + bytesRead;
}
raf.close();
bis.close();
} catch (ClientProtocolException e) {
LOGGER.error("DownloadThread exception msg:{}", ExceptionUtils.getFullStackTrace(e));
} catch (IOException e) {
LOGGER.error("DownloadThread exception msg:{}", ExceptionUtils.getFullStackTrace(e));
} finally {
end.countDown();
LOGGER.info(end.getCount() + " is go on!");
System.out.println(end.getCount() + " is go on!");
}
}
}