DBFileDownloadServlet.java

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;
 

@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/newfilesdb";
    private String dbUser = "root";
    private String dbPass = "sainath";
     
    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";
                }              
           

/*
if (mimeType == null)
{
mimeType = "application/pdf";
}
*/
     
                // 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();
                }
            }          
        }
    }
}