Java servlet to download file from database

http://www.codejava.net/java-ee/servlet/java-servlet-to-download-file-from-database







package net.codejava.servlet;

 

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.sql.Blob;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

 

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

/**

 * A servlet that retrieves a file from MySQL database and lets the client

 * downloads the file.

 * @author www.codejava.net

 */

@WebServlet("/downloadFileServlet")

public class DBFileDownloadServlet extends HttpServlet {

 

    // size of byte buffer to send file

    private static final int BUFFER_SIZE = 4096;   

     

    // database connection settings

    private String dbURL = "jdbc:mysql://localhost:3306/FileDB";

    private String dbUser = "root";

    private String dbPass = "secret";

     

    protected void doGet(HttpServletRequest request,

            HttpServletResponse response) throws ServletException, IOException {

        // get upload id from URL's parameters

        int uploadId = Integer.parseInt(request.getParameter("id"));

         

        Connection conn = null; // connection to the database

         

        try {

            // connects to the database

            DriverManager.registerDriver(new com.mysql.jdbc.Driver());

            conn = DriverManager.getConnection(dbURL, dbUser, dbPass);

 

            // queries the database

            String sql = "SELECT * FROM files_upload WHERE upload_id = ?";

            PreparedStatement statement = conn.prepareStatement(sql);

            statement.setInt(1, uploadId);

 

            ResultSet result = statement.executeQuery();

            if (result.next()) {

                // gets file name and file blob data

                String fileName = result.getString("file_name");

                Blob blob = result.getBlob("file_data");

                InputStream inputStream = blob.getBinaryStream();

                int fileLength = inputStream.available();

                 

                System.out.println("fileLength = " + fileLength);

 

                ServletContext context = getServletContext();

 

                // sets MIME type for the file download

                String mimeType = context.getMimeType(fileName);

                if (mimeType == null) {        

                    mimeType = "application/octet-stream";

                }              

                 

                // set content properties and header attributes for the response

                response.setContentType(mimeType);

                response.setContentLength(fileLength);

                String headerKey = "Content-Disposition";

                String headerValue = String.format("attachment; filename=\"%s\"", fileName);

                response.setHeader(headerKey, headerValue);

 

                // writes the file to the client

                OutputStream outStream = response.getOutputStream();

                 

                byte[] buffer = new byte[BUFFER_SIZE];

                int bytesRead = -1;

                 

                while ((bytesRead = inputStream.read(buffer)) != -1) {

                    outStream.write(buffer, 0, bytesRead);

                }

                 

                inputStream.close();

                outStream.close();             

            } else {

                // no file found

                response.getWriter().print("File not found for the id: " + uploadId);  

            }

        } catch (SQLException ex) {

            ex.printStackTrace();

            response.getWriter().print("SQL Error: " + ex.getMessage());

        } catch (IOException ex) {

            ex.printStackTrace();

            response.getWriter().print("IO Error: " + ex.getMessage());

        } finally {

            if (conn != null) {

                // closes the database connection

                try {

                    conn.close();

                } catch (SQLException ex) {

                    ex.printStackTrace();

                }

            }          

        }

    }

}