How to grab byte[] of an Image in java?

Question

I have a url of an Image. Now I want to get the byte[] of that image. How can I get that image in byte form.

Actually the image is a captcha image. I am using decaptcher

Answer 1

EDIT

From this SO question I've got how to read an input stream into a byte array.

Here's the revised program.

import java.io.*;
import java.net.*;

public class ReadBytes {
    public static void main( String [] args ) throws IOException {

        URL url = new URL("http://sstatic.net/so/img/logo.png");

            // Read the image ...
        InputStream inputStream      = url.openStream();
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        byte [] buffer               = new byte[ 1024 ];

        int n = 0;
        while (-1 != (n = inputStream.read(buffer))) {
           output.write(buffer, 0, n);
        }
        inputStream.close();

        // Here's the content of the image...
        byte [] data = output.toByteArray();

    // Write it to a file just to compare...
    OutputStream out = new FileOutputStream("data.png");
    out.write( data );
    out.close();

    // Print it to stdout 
        for( byte b : data ) {
            System.out.printf("0x%x ", b);
        }
    }
}

This may work for very small images. For larger ones, ask/search about "read input stream into byte array"

Now the code I posted works for larger images too.

Answer 2

If you want the byte string as it is stored on disk, just create a socket and open the image file. Then read the bytes as they come down the wire.

I don't have any sample code handy and it's been a while since I've done this, so excuse me if I've got the details wrong to be sure I give this to you straight, but the basic idea would be:

URL imageUrl=new URL("http://someserver.com/somedir/image.jpg");
URLConnection imageConnect=imageUrl.openConnection();
imageConnect.connect();
InputStream is=imageConnect.getInputStream();
... read from the input stream ...

Answer 3

You may want to read this for reading an image in. ImageIO.Read(url) will give you a Buffered Image Which you can then ask for information. I use the getRGB method on BufferedReader to read individual pixels.