The easiest and elegant way to read images from the database and display them in the UI is through a servlet that handles the image processing for you. I’ll present below a sample that displays a user avatar in the jsp page. This sample uses Spring 3 and the tip from this article to inject a spring bean into this servlet. This example can easily be adapted to many kinds of situations. Here is the code:

The servlet

package insidecoding.servlet;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.HttpRequestHandler;

import insidecoding.service.UserService;

@Component("imageServlet")
public class ImageServlet implements HttpRequestHandler {

    @Autowired
    private UserService UserService;

    @Override
    public void handleRequest(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // get the thumb from the user entity
        byte[] thumb = userService.getCurrentUserAvatar();

        String name = "userAvatar";
        response.setContentType("image/jpeg");
        response.setContentLength(thumb.length);

        response.setHeader("Content-Disposition", "inline; filename=\"" + name
                + "\"");

        BufferedInputStream input = null;
        BufferedOutputStream output = null;

        try {
            input = new BufferedInputStream(new ByteArrayInputStream(thumb));
            output = new BufferedOutputStream(response.getOutputStream());
            byte[] buffer = new byte[8192];
            int length;
            while ((length = input.read(buffer)) > 0) {
                output.write(buffer, 0, length);
            }
        } catch (IOException e) {
            System.out.println("There are errors in reading/writing image stream "
                    + e.getMessage());
        } finally {
            if (output != null)
                try {
                    output.close();
                } catch (IOException ignore) {
                }
            if (input != null)
                try {
                    input.close();
                } catch (IOException ignore) {
                }
        }

    }
}

Map this servlet to the /image path in web.xml

     <servlet>
        <servlet-name>imageServlet</servlet-name>
        <servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>imageServlet</servlet-name>
        <url-pattern>/image/*</url-pattern>
    </servlet-mapping>

Usage in JSP

....
<img src="image/avatar" height="75px" width="75px" align="left" />
....

The code is pretty self-explanatory:

• get the byte[] array from the database
• wrap it with an InputStream
• write the data from the InputStream to the servlet output stream in chunks

This code version supposes that you want to display the avatar of the current logged user. But this servlet can be used with any type of situation. For example, if you want to display images by the imageId, you can do this:

....
<img src="image/1212" height="75px" width="75px" align="left" />
....

Where 1212 is the imageId. You can then grab this imageId in the servlet, get the corresponding byte[] from the DB and continue as in the above code.

Nice, elegant and easy.

If you have questions please leave a comment below.