Java EE (Java Enterprise Edition) General Discussion

There is much talk about how to display images through JSP pages or Servlets when they are stored in a database as a Blob field, I personally found it quite ideal to use a servlet and simply invoke it through a dynamic page with the following method:

Notice that the following example can be invoked either statically or dynamically:

Static Context

<img src='showImage?id=1>

Dynamic Context

<img src='showImage?id=" + ImageID + "'>

The following is the servlet that will handle the invocation sent from above (both doPost and doGet)
Furthermmore it has been simulated for mySQL Database and the stored attribute is a blob jpeg image.

showImage.java

import java.io.*;
import java.text.*;
import java.sql.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

/**
 *
 * Author:  Kyriakos T. Fourniadis
 * Scope:   Display Image Servlet
 * Version: 1.0
 *
 */

public class showImage extends HttpServlet {
    
    private Connection con;
    private Statement stmt;
    private String trace;
    
    /**
     * Setup database connection and create SQL statement
     */
    public void init( ServletConfig config ) throws ServletException
    {
        // Try database connection
        try{
            // The call to Class.forName explicitly loads the driver class
            //Class.forName("org.gjt.mm.mysql.Driver"); 
            Class.forName("com.mysql.jdbc.Driver").newInstance(); 
            //jdbc:mysql://<HOST>:<PORT>/<DB>
            //Connection con = DriverManager.getConnection("jdbc:mysql://localhost/mydb?user=''&password=''");
            con = DriverManager.getConnection("jdbc:mysql://localhost/mydb");
            // Once a connection has been established we can create an instance 
            // of Statement, through which we will send queries to the database.
            stmt = con.createStatement();  
        }
        catch (Exception exception ) {
            exception.printStackTrace();
            throw new UnavailableException(exception.getMessage());
        }
    } // End init()
    
    /**
     * Forward to doGet
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        doPost(request, response);
    }
    
    /*
     * NOTE: doPost -> HTTP post requests | doGet -> HTTP get resuest
     */
    public void doPost(HttpServletRequest request, HttpServletResponse response)
    throws IOException, ServletException
    {
        // Simple trace variable for debugging...
        trace = "";
        
        /*
        SELECT *
        FROM image
        WHERE image.image_id = ?variable?
         */        
        try {
            String SQL =
                "SELECT * " +
                "FROM image " +
                "WHERE image.image_id = '" + request.getParameter("id") + "'";
            
            ResultSet rs = stmt.executeQuery(SQL);
            rs.next();
            
            Blob blob = null;
            blob = rs.getBlob("image");
            response.setContentType("image/jpeg");
            
            System.out.println("just above OutputStream");
            
            InputStream in = blob.getBinaryStream();
            OutputStream out = response.getOutputStream();
            int b;
            while ((b = in.read()) != -1) {
                out.write(b);
            }

            in.close();
            out.flush();
            out.close(); 

        }
        catch (Exception exception ) {
            throw new ServletException("Error");
        }
    } // end doPost()
            
    /*
     * Close SQL statements & database connection
     */
    public void destroy()
    {
        // Attempt to close statements and database connection
        try{
            stmt.close();
            con.close();
        }       
        
        // Handle database exceptions by returning error to client
        catch (SQLException sqlException){
            sqlException.printStackTrace();
        }
    } // End destroy()    
} // End class showImage

web.xml

<!DOCTYPE web-app PUBLIC 
   "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN" 
   "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">

<web-app>
   <!-- General description of your Web application -->
   <display-name>
      Kyriakos T. Fourniadis Java Tech. Example
   </display-name>

   <!-- showImage definitions -->
   <servlet>
      <servlet-name>showImage</servlet-name>
      <description>
           Display Image
      </description>
      <servlet-class>
           showImage
      </servlet-class>
   </servlet>

   <servlet-mapping>
        <servlet-name>showImage</servlet-name>
        <url-pattern>showImage</url-pattern>
   </servlet-mapping>

</web-app>

This code is virtually plug & play, the only modification you will need is to modify the database connection and the web.xml file. Remember that the example can be invoked either from a static HTML page or request, a dynamic JSP page, or a Servlet.

Author: Kyriakos T. Fourniadis