Java 实现一个简单的文件下载 servlet
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Implementing a simple file download servlet
提问by newbie
How should I implement simple file download servlet?
我应该如何实现简单的文件下载servlet？
The idea is that with the GET request index.jsp?filename=file.txt, the user can download for example. file.txtfrom the file servlet and the file servlet would upload that file to user.
这个想法是，通过 GET 请求index.jsp?filename=file.txt，用户可以下载例如。file.txt从文件 servlet 和文件 servlet 将该文件上传给用户。
I am able to get the file, but how can I implement file download?
我能够获取文件，但是如何实现文件下载？
采纳答案by ChssPly76
That depends. If said file is publicly available via your HTTP server or servlet container you can simply redirect to via response.sendRedirect().
那要看。如果该文件可通过您的 HTTP 服务器或 servlet 容器公开访问，您只需重定向到 via response.sendRedirect().
If it's not, you'll need to manually copy it to response output stream:
如果不是，您需要手动将其复制到响应输出流：
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();
You'll need to handle the appropriate exceptions, of course.
当然，您需要处理适当的异常。
回答by Winston Chen
The easiest way to implement the download is that you direct users to the file location, browsers will do that for you automatically.
实现下载的最简单方法是将用户定向到文件位置，浏览器会自动为您执行此操作。
You can easily achieve it through:
您可以通过以下方式轻松实现：
HttpServletResponse.sendRedirect()
回答by Ali Irawan
Assuming you have access to servlet as below
假设您可以访问 servlet，如下所示
http://localhost:8080/myapp/download?id=7
I need to create a servlet and register it to web.xml
我需要创建一个 servlet 并将其注册到 web.xml
web.xml
网页.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>
DownloadServlet.java
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();
}
}
回答by Sorter
Try with Resource
用资源试试
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();
