我该如何实现简单的文件下载servlet?
思路是通过GET请求index.jsp?filename=file.txt
,用户可以从文件servlet下载例如file.txt
这样的文件,并将该文件上传给用户。
我能够获取文件,但是如何实现文件下载呢?
http://localhost:8080/myapp/download?id=7
我需要创建一个servlet并将其注册到web.xml中
web.xml
<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>
下载Servlet.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();
}
}
while ((length = in.read(buffer)) > -1)
- reformy这取决于情况。如果该文件可以通过您的HTTP服务器或Servlet容器公开访问,您可以使用response.sendRedirect()
进行重定向。
如果不能公开访问,则需要手动将其复制到响应输出流中:
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,你需要处理适当的异常。
while ((length = in.read(buffer)) > -1)
- reformyFile 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();
最简单的实现下载的方式是直接将用户引导到文件位置,浏览器会自动完成下载。
您可以通过以下方式轻松实现:
HttpServletResponse.sendRedirect()
发送大文件
byte[] pdfData = getPDFData();
String fileType = "";
res.setContentType("application/pdf");
httpRes.setContentType("application/.pdf");
httpRes.addHeader("Content-Disposition", "attachment; filename=IDCards.pdf");
httpRes.setStatus(HttpServletResponse.SC_OK);
OutputStream out = res.getOutputStream();
System.out.println(pdfData.length);
out.write(pdfData);
System.out.println("sendDone");
out.flush();