实现一个简单的文件下载servlet
我应该如何实现简单的文件下载servlet？
这个想法是，用GET请求index.jsp?filename=file.txt ，用户可以下载例如。 文件servlet中的file.txt和文件servlet会将该file upload到用户。
我能够得到该文件，但我怎样才能实现文件下载？
那要看。 如果所述文件通过HTTP服务器或servlet容器公开可用，则可以简单地通过response.sendRedirect()redirect到该文件。
如果不是，则需要手动将其复制到响应输出stream：
OutputStream out = response.getOutputStream(); FileInputStream in = new FileInputStream(my_file); byte[] buffer = new byte[4096]; int length; while ((length = in.read(buffer)) > 0){ out.write(buffer, 0, length); } in.close(); out.flush();
当然，你需要处理适当的例外。
假设您有权访问servlet，如下所示
http://localhost:8080/myapp/download?id=7
我需要创build一个servlet并将其注册到web.xml
web.xml中
<servlet> <servlet-name>DownloadServlet</servlet-name> <servlet-class>com.myapp.servlet.DownloadServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>DownloadServlet</servlet-name> <url-pattern>/download</url-pattern> </servlet-mapping>
DownloadServlet.java
public class DownloadServlet extends HttpServlet { protected void doGet( HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String id = request.getParameter("id"); String fileName = ""; String fileType = ""; // Find this file id in database to get file name, and file type // You must tell the browser the file type you are going to send // for example application/pdf, text/plain, text/html, image/jpg response.setContentType(fileType); // Make sure to show the download dialog response.setHeader("Content-disposition","attachment; filename=yourcustomfilename.pdf"); // Assume file name is retrieved from database // For example D:\\file\\test.pdf File my_file = new File(fileName); // This should send the file to browser OutputStream out = response.getOutputStream(); FileInputStream in = new FileInputStream(my_file); byte[] buffer = new byte[4096]; int length; while ((length = in.read(buffer)) > 0){ out.write(buffer, 0, length); } in.close(); out.flush(); } }
尝试使用资源
File file = new File("Foo.txt"); try (PrintStream ps = new PrintStream(file)) { ps.println("Bar"); } response.setContentType("application/octet-stream"); response.setContentLength((int) file.length()); response.setHeader( "Content-Disposition", String.format("attachment; filename=\"%s\"", file.getName())); OutputStream out = response.getOutputStream(); try (FileInputStream in = new FileInputStream(file)) { byte[] buffer = new byte[4096]; int length; while ((length = in.read(buffer)) > 0) { out.write(buffer, 0, length); } } out.flush();
实现下载最简单的方法是将用户引导至文件位置，浏览器将自动为您执行此操作。
您可以通过以下方式轻松实现：
HttpServletResponse.sendRedirect()
