Java Servlet-将数据写入文件

Question

I have a servlet which uses file with data. The relative path to this file is contained in web.xml. I have following part of code, which reads data from file:

public class LoginServlet extends HttpServlet {
private Map<String, UserData> users;
public void init() throws ServletException {
    super.init();
    String userFilePath = getServletContext().getInitParameter("user.access.file");
    InputStream userFile = this.getClass().getResourceAsStream(userFilePath);
    try {
        users = readUsersFile(userFile);
    } catch (IOException e) {
        e.printStackTrace();
        throw new ServletException(e);
    }
            ....
            ....
    }

private Map<String, UserData> readUsersFile(InputStream is) throws IOException{
    BufferedReader fileReader = new BufferedReader(new InputStreamReader(is));
    Map<String, UserData> result = new HashMap<String, UserData>();
            ....
            ....
            ....
            return result;
     }
}

Because this is a servlet and it will not work only on my PC, I can't use absolute path. Does anyone know how I can write data to the file, using a similar way?

Answer 1

If the resource URL is resolveable to an absolute local disk file system path and it is writable, then you can use

URL url = this.getClass().getResource(userFilePath);
File file = new File(url.toURI().getPath());
OutputStream output = new FileOutputStream(file);
// ...

This is however in turn not guaranteed to work on all environments.

Your best bet is really to have a fixed and absolute local disk file system path. The normal practice is however to store structured data (usernames/password) in a database and not a file.