Servlet断点续传下载

最新推荐文章于 2022-12-08 18:15:28 发布

原创最新推荐文章于 2022-12-08 18:15:28 发布 · 1.4k 阅读

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文章标签：

#servlet #string #buffer #file #download #byte

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本文介绍了一个使用Java Servlet实现的文件下载服务。该服务通过解析HTTP请求来定位文件位置，并支持断点续传功能。文章详细展示了如何设置响应头以允许客户端进行文件下载。

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package baiyang;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URLDecoder;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Download
 */
@WebServlet("/download/*")
public class DownloadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public DownloadServlet() {
		super();
	}

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		response.setCharacterEncoding("GBK");
		String requestUrl = new String(URLDecoder.decode(request.getRequestURI(), "UTF-8"));
		System.out.println("请求地址" + requestUrl);
		if (requestUrl.endsWith("/download/") || requestUrl.endsWith("/download")) {
			PrintWriter pw = response.getWriter();
			Error404(pw);
			return;
		}
		// 获取文件
		String filePath = this.getServletConfig().getServletContext().getRealPath("/") + requestUrl.substring(requestUrl.indexOf("/download") + 10);
		System.out.println("文件路径：" + filePath);
		File file = new File(filePath);
		if (!file.exists()) {
			System.out.println("文件“" + file.getAbsolutePath() + "”不存在!");
			PrintWriter pw = response.getWriter();
			Error404(pw);
			return;
		}
		OutputStream os = response.getOutputStream();
		long start = 0;
		String range = request.getHeader("range");
		if (range != null) {
			System.out.println("range=" + range);
			String rg = range.split("=")[1];
			start = Long.parseLong(rg.split("-")[0]);
			response.setStatus(206);
		}
		response.setContentType("application/octet-stream;charset=UTF-8");
		response.setHeader("Accept-Ranges", "bytes");
		response.setHeader("Content-Range", "bytes  " + start + "-" + (file.length() - 1) + "/" + file.length());
		response.setHeader("Content-Length", " " + file.length());
		response.setHeader("Content-Disposition", "attachment; filename=\"" + new String(file.getName().getBytes(), "ISO-8859-1") + "\"");
		InputStream is = new FileInputStream(file);
		System.out.println("start=" + start);
		is.skip(start);
		byte[] buffer = new byte[1024 * 64];
		int len = 0;
		while ((len = is.read(buffer, 0, buffer.length)) != -1) {
			os.write(buffer, 0, len);
		}
		os.flush();
		os.close();
		is.close();
		System.out.println("下载完成!");
	}

	private static void Error404(PrintWriter pw) {
		String msg = "<html><title>未找到……</title><body>";
		msg += "<div style='color:red;text-align:center'>抱歉!未找到您要下载的资源……<br><input type='button' value='返回' onclick='javascrip:history.go(-1)'></div>";
		msg += "</body></html>";
		pw.write(msg);
		pw.flush();
		pw.close();
	}
}