Servlet - Downloading File

Servlets provide a way to build server-side Java applications that can handle HTTP requests and generate dynamic responses. File downloading in Servlets allows users to download files stored on the server directly through a browser. In this process, the server reads the file and sends it to the client using response streams.

Used to download files like images, PDFs, ZIP, and documents
Uses HttpServletResponse to write file data to output stream
Sets response headers to control file download behavior

How File Download Works in Servlet

When a user requests a file, the servlet reads the file from the server directory and writes its content to the response output stream. The browser then downloads the file instead of displaying it.

The servlet sets response headers like Content-Disposition to force the browser to download the file.
The file is transferred as a byte stream using InputStream and OutputStream for efficient data handling.

Important Methods Used

Method	Description
`getParameter()`	Gets file name from request
`FileInputStream`	Reads file from server
`getOutputStream()`	Sends file to browser
`setHeader()`	Sets download file name

Step by Step Implementation to Download File

This example demonstrates how a file (like .docx, .pdf, .png) can be downloaded from the server using a Servlet. The servlet reads the file from the server directory and sends it to the browser using response streams.

Step 1: Create Dynamic Web Project

Open Eclipse IDE
Create a project: ServletFilterchain
Select: Dynamic Web Project
Click Finish

Step 2: Create HTML Page (index.html)

This form triggers a GET request to the servlet mapped at /download when the user clicks the Download button. The request is sent directly to the server without any input data. The servlet then processes the request and initiates the file download response.

HTML

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Welcome</title>
</head>
<body>
    <form action="download" method="get">
        <h2>Welcome to GeeksforGeeks.</h2>
        <h3>Download the updated Data structures course structure here.</h3>
        <input type="submit" value="Download" />
    </form>
</body>
</html>

Step 3: Create Download Servlet

This servlet handles a GET request at /download and reads a file from the server using FileInputStream, then writes it to the response output stream so the browser downloads it as an attachment.

Java

import java.io.FileInputStream;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/download")
public class Download extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response)
            throws ServletException, IOException {

        // File name
        String fileName = "DataStructures.docx";

        // File location on server
        String filePath = "E:\\";

        // Set response content type
        response.setContentType("application/msword");

        // Force browser to download the file
        response.setHeader("Content-Disposition",
                "attachment; filename=\"" + fileName + "\"");

        // Read the file from server
        FileInputStream inputStream =
                new FileInputStream(filePath + fileName);

        // Get output stream
        ServletOutputStream out = response.getOutputStream();

        // Write file to browser
        byte[] buffer = new byte[4096];
        int bytesRead;

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

        // Close resources
        inputStream.close();
        out.flush();
        out.close();
    }
}

Step 4: web.xml (Optional if not using annotation)

The web.xml file is used to manually configure and map the servlet with a specific URL pattern. It acts as a deployment descriptor that tells the server which servlet should be executed when a particular request URL is accessed.

XML

<web-app>

    <servlet>
        <servlet-name>Download</servlet-name>
        <servlet-class>Download</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>Download</servlet-name>
        <url-pattern>/download</url-pattern>
    </servlet-mapping>

</web-app>

Step 5: Run the Application

Start Apache Tomcat Server
Deploy the project in IDE (Eclipse/IntelliJ)
Run the application
Open browser and hit:

http://localhost:8081/DownloadServlet/index.html

Output:
your browser will open with:

Once we click Download, the document will be downloaded in the browser like below.

Explanation: This servlet handles a file download request by reading a file from the server directory using FileInputStream. It sets proper response headers like Content-Type and Content-Disposition to force the browser to download the file instead of displaying it. The file content is then written to the response output stream and sent to the client for download.