How to Stream the Content of an Arbitrary File in a Java Web Application

Question

What is the process for streaming the content of an arbitrary file to a browser in a Java web application?

// Example code for streaming a file contents to a web browser
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class FileStreamServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String filePath = request.getParameter("filePath");
        File file = new File(filePath);

        // Set content type and headers
        response.setContentType("text/plain");
        response.setHeader("Content-Disposition", "attachment; filename=" + file.getName());

        // Stream the file to the response output
        try (FileInputStream fileInputStream = new FileInputStream(file);
             OutputStream outputStream = response.getOutputStream()) {
            byte[] buffer = new byte[4096];
            int bytesRead;

            while ((bytesRead = fileInputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
        }
    }
}

Answer

Streaming the content of an arbitrary file to a browser in a Java web application involves using a servlet to handle HTTP requests, reading the file, and writing its content to the HTTP response. This process allows users to receive real-time file updates in their browsers, which is particularly useful for log files or other live data sources.

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class LiveTailServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String filePath = request.getParameter("filePath");
        File file = new File(filePath);

        response.setContentType("text/plain");
        response.setHeader("Content-Disposition", "inline; filename=" + file.getName());

        try (BufferedReader reader = new BufferedReader(new FileReader(file));
             PrintWriter writer = response.getWriter()) {
            String line;
            while ((line = reader.readLine()) != null) {
                writer.println(line);
                writer.flush();
                Thread.sleep(1000); // simulate real-time streaming
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }

Causes

Incorrect file path specified in the request.
Improper handling of input/output streams leading to resource leaks.
Incorrect MIME type set in the response.

Solutions

Ensure the file path is absolute and accessible by the server.
Use try-with-resources statement for safe input/output stream management.
Set the appropriate MIME type for the file being streamed.

Common Mistakes

Mistake: Not validating the file path.

Solution: Always validate the file path to avoid unauthorized access or file not found exceptions.

Mistake: Not managing resources properly.

Solution: Utilize try-with-resources to ensure streams are closed properly after use.

Mistake: Incorrect content type may result in browser incompatibility.

Solution: Set the content type properly according to the file being served.

Helpers

Java web application
file streaming in Java
stream file content
live tailing in Java
Java servlets
real-time file streaming