java远程文件下载,支持文件断点续传
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核心提示:import java.io.File;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;
import java.io.File; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; import java.text.SimpleDateFormat; import java.util.Date; import org.apache.log4j.Logger; /** * 远程文件下载,支持文件断点续传 * @author ketqi */ public class FileDownload { private Logger logger = Logger.getLogger(FileDownload.class); private static final SimpleDateFormat FORMAT = new SimpleDateFormat("yyyyMMddHHmmss"); // 远程文件的url private URL url; // 下载完后的目标临时文件 private File tempFile; // 失败次数 private int count = 0; public FileDownload(String url) throws Exception { this.url = new URL(url); tempFile = File.createTempFile(FORMAT.format(new Date()), ".xml"); } /** * @category 支持断点续传的受控端下载 * @param fileLength * 读取远程文件的开始位置 * @return */ public void execute(long fileLength) { long currentSize = fileLength; HttpURLConnection httpConnection = null; InputStream input = null; RandomAccessFile targetFile = null; try { httpConnection = (HttpURLConnection) url.openConnection(); // 设置User-Agent httpConnection.setRequestProperty("User-Agent", "NetFox"); // 设置断点续传的开始位置 httpConnection.setRequestProperty("RANGE", "bytes=" + fileLength + "-"); // 获得输入流 input = httpConnection.getInputStream(); targetFile = new RandomAccessFile(tempFile, "rw"); // 定位文件指针到fileLength位置 targetFile.seek(fileLength); byte[] b = new byte[1024]; int nRead; // 从输入流中读入字节流,然后写到文件中 while ((nRead = input.read(b, 0, 1024)) > 0) { (targetFile).write(b, 0, nRead); currentSize += nRead; } } catch (Exception e) { logger.error(e.getMessage(), e); e.printStackTrace(); // 60秒钟的间隔进行再次尝试连接 logger.info("等待60秒后再次进行断点下载"); try { Thread.sleep(60000); } catch (Exception e1) { } // 续传 if (currentSize < getRemoteFileSize()) { logger.info("在" + currentSize + "续传"); //续传已超过20次放弃下载 if (count < 20) { execute(currentSize); } } } finally { if (targetFile != null) { try { targetFile.close(); } catch (Exception e) { } targetFile = null; } if (input != null) { try { input.close(); } catch (IOException e) { } input = null; } if(httpConnection != null){ httpConnection.disconnect(); } } } /** * @category 已下载的文件 * @return */ public File getFile() { return tempFile; } /** * @category 获得远程文件大小 * @return */ public long getRemoteFileSize() { long size = 0; try { HttpURLConnection conn = (HttpURLConnection) url.openConnection(); size = conn.getContentLength(); conn.disconnect(); } catch (Exception e) { e.printStackTrace(); } return size; } }
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