Error in Dowlnoading

[vinoth ar]

hi friends..

here i tried to write program to download a jpeg image from folder Resource folder. it is downloading a jpeg image as ordinary file with 0 bytes. with name of file as dload(servlet name). i couln`t trace the logical could you correct me..

   import java.io.*; 
import javax.servlet.*;
import javax.servlet.http.*;


public class dload extends HttpServlet 
{
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException 
{
        response.setContentType("image/jpeg");
        OutputStream os =   response.getOutputStream();
        try 
        {
            ServletContext context = getServletContext();
            InputStream is = context.getResourceAsStream("/Resource/vino.jpeg");
            
            byte []bytes = new byte[46000];
            is.read(bytes);
            int read = 0;
            boolean flag = true;
            while(flag)
            {
               read = is.read(bytes);
               if(read == -1){ flag = false;break;}
               else{ flag = true;}
               os.write(bytes,0,read);
            }
        } finally 
        { 
            os.flush();
            os.close();
        }
    } 

 

thank you...

[Bauke Scholtz]

You´re forgotten to set the response headers content-length and content-disposition.

[vinoth ar]

hi Bauke Scholtz,

can you please explain me. why we need those functions. i`ve some knowledge about setcontentlen explght().. no knowledge about diposition.

can you explain for me.

thanks

[Bauke Scholtz]

Uh. There is no why. The HTTP specification state so.

[vinoth ar]

hi Bauke Scholtz ,
i can`t get you. anyways thanks for your. kind reply.

[Bauke Scholtz]

It´s just, say, the law of HTTP.

http://www.w3.org/Protocols/rfc2616/rfc2616.html

Asking "why so?" makes no sense. It´s just because it is definied so.

[Paul Clapham]

It also doesn't help that you read and discarded an unknown number of bytes from the JPG before your loop that tries to copy it to the response.

[Hendy Setyo Mulyo]

vinoth ar wrote:hi friends..

here i tried to write program to download a jpeg image from folder Resource folder. it is downloading a jpeg image as ordinary file with 0 bytes. with name of file as dload(servlet name). i couln`t trace the logical could you correct me..

First, you should make sure that the image file you want to download is in the correct path.

InputStream is = context.getResourceAsStream("/Resource/vino.jpeg");

In other words, you should check whether is != null;

[Bauke Scholtz]

I have not checked the code closely, but all of above is ultimately correct. Your code is not robust enough.
You may find this example useful then: http://balusc.blogspot.com/2007/04/imageservlet.html

Besides, using POST for this makes no sense. Rather use GET. The <img src> always use GET. And no, you shouldn't call doPost() inside doGet().

[Paul Clapham]

In particular line #19 will read up to 46000 bytes of the resource into a byte array. You ignore this and just stream the rest of the resource out to the response.

[Edwin Stephens]

Hello Vinoth,

You can also use the ImageIO class to read the jpeg image file and write it to the response output stream, like this:

response.setContentType("image/jpeg");
File f = new File("/Resource/vino.jpeg");
BufferedImage bi = ImageIO.read(f);
OutputStream out = response.getOutputStream();
ImageIO.write(bi, "jpg", out);
out.close();

This technique is detailed here:
http://www.avajava.com/tutorials/lessons/how-do-i-return-an-image-from-a-servlet-using-imageio.html

Hope that helps,
Edwin