How can I display images from a HTTP Web Server?

Question

I am trying to display images inside my HTTP Web Server but I'm unable to. I can display the HTML. I think it is something to do with the way I handle my IO (input and output streams). There's probably a lot of mistakes in there that I haven't noticed.

import java.io.* ;
import java.net.* ;
import java.util.Properties;


public class HTTPThread extends Thread
{
    private Socket socket = null;
    private Properties config = null;
    private String root = "";

    public HTTPThread(Socket s, Properties config)
    {
        this.socket = s;
        this.config = config;
        this.root = this.config.getProperty("root");        
    }

    public void run()
    {   

//      InputStream in = null;
        OutputStream out = null;

        try
        {
            out = socket.getOutputStream();
            PrintWriter writer = new PrintWriter(out, true);

            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String request = reader.readLine();
            writer.println("HTTP/1.1 200 OK");
            writer.println("Content-Type: text/html");          
            writer.println();

            // Search for filename 
            int slash = request.indexOf("/"); //find first occurrence of slash
            int emptySpace = request.indexOf(" ", slash); //find first space after slash
            String filename = request.substring(slash, emptySpace); //return filename 
//          writer.println("<b>" + filename + "</b>");

            String pathname = "";
            try
            {
                pathname = (filename == "/") ? root + filename : root;
//              System.out.println(filename);           
                URL url = new URL(pathname);
                URLConnection urlc = url.openConnection();
                BufferedReader in = new BufferedReader(
                        new InputStreamReader(
                        urlc.getInputStream()));

                String line;                
                while ((line = in.readLine()) != null)
                {
                    writer.println(line);
                }
                in.close();
            }
            catch (MalformedURLException e)
            {
                System.err.println("Don't know about host: " + pathname);
                System.exit(1);
            }
            catch (IOException e)
            {
                  System.err.println("Couldn't get I/O for "
                                     + "the connection to: " + pathname);
                  System.exit(1);
            }



//          reader.close();
            writer.close();
            socket.close();
        }
        catch(IOException e)
        {
            System.out.println("Error: " + e);          
        }

        finally
        {
            try
            {
//              in.close() ;
                out.close() ;
                socket.close();
            }
            catch(IOException e)
            {
                System.out.println("Error: " + e);          
            }
        }
    }
}

Tomasz Nurkiewicz · Accepted Answer · 2012-10-16 19:48:05Z

3

Are you trying to write some sort of proxy server that takes external URL from the request and returns the contents? Well, there are several issues with your code:

writer.println("HTTP/1.1 200 OK");
writer.println("Content-Type: text/html");

When browser sees the above, it assumes whatever is returned is HTML. Rendering binary image as HTML will clearly fail. Which leads us to this:

String line;                
while ((line = in.readLine()) != null)
{
    writer.println(line);
}
in.close();

In the loop above you are reading some external URL line-by-line (in text mode) and forwarding it to original client. This works for HTML (which is text-based) but will fail for any image (binary). You must use InputStream/OutputStream instead.

And small thing at the end:

pathname = (filename == "/") ? root + filename : root;

Do not compare strings using == operator, replace it with:

pathname = (filename.equals("/")) ? root + filename : root;

As a final note, consider using servlet container like Tomcat or Jetty, which will release you from HTTP-handling code and provide more high-level constructs.

answered Oct 16, 2012 at 19:48

Tomasz Nurkiewicz

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2 Comments

Johnathan Au Over a year ago

Thanks. Can you point to something that guides me how I can input images from an URL and output to a browser like I am doing here? I've tried searching google but can't find anything =/

Tomasz Nurkiewicz Over a year ago

@JohnathanAu: start from stackoverflow.com/questions/43157 and understand the difference between Reader and InputStream.

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