directly saving an image to a file?

[Kyle Rayner]

Greetings. I already managed to acquire an image by using the BufferedImage class - and with some fiddling I found out how I can save it to a file, BUT...

...the thing is, I'd like the image to be saved without being recompressed so that the resulting image file is a 1:1 copy of what I started with.

If someone says "why not just copy it then" - I'm retrieving the image from the web, so I can't just copy it. (erh... or can I?)

Kyle

[Keith Lynn]

Here is one way of doing it.

import java.io.*;
import java.awt.*;
import java.net.*;
 
public class RetrieveImage {
   public static String errorcode = "";
 
   public static byte[] getURL(String url) {
      try {
[I]// Open a connection to URL to read bytes[/I]
         BufferedInputStream input = new BufferedInputStream(new URL(url).openStream());
 
[I]// Initialize an array of bytes which will eventually hold all of
// the bytes of the URL.[/I]
         byte[] bytes = new byte[0];
 
[I]// Initialize a buffer array which will be used to hold a large
// number of bytes at a time.[/I]
         byte[] buffer = new byte[4000*1024];
 
         int length = 0;
 
[I]// While there are still bytes to read[/I]
         while ((length = input.read(buffer,0,buffer.length)) != -1) {
[I]// Create a temporary byte array large enough to contain the contents
// of bytes and the contents of buffer.[/I]
            byte[] temp = new byte[bytes.length+length];
 
[I]// Copy the contents of the original array into the new array.[/I]
            System.arraycopy(bytes,0,temp,0,bytes.length);
[I]// Copy the contents of the buffer into the new array.[/I]
            System.arraycopy(buffer,0,temp,bytes.length,length);
 
[I]// Rearrange the array pointer to point to the new array[/I].
            bytes = temp;
         }
 
[I]// Close the input stream.[/I]
         input.close();
 
[I]// Return the byte array.[/I]
         return(bytes);
      } catch (IOException ie) {
[I]// Add the String representation of the exception that occurred to the
// errorcode.[/I]
         errorcode += ie;
 
[I]// Return an empty byte array to match the return type of the method.[/I]
         return(new byte[0]);
      }
   }
 
   public static void store(String fileName,
                            byte[] bytes) {
      try {
[I]// Open a connection to an external file to write a stream of bytes.[/I]
         FileOutputStream file = new FileOutputStream(fileName);
[I]// For efficiency wrap it in a BufferedOutputStream.[/I]
         BufferedOutputStream output = new BufferedOutputStream(file);
 
[I]// Now write the entire byte array to the file.[/I]
         output.write(bytes,0,bytes.length);
 
[I]// Close the output stream to make sure that all of the bytes are written
// to the file.[/I]
         output.close();
      } catch (IOException ie) {
[I]// Add the String representation of the exception that occurred to the
// errorcode.[/I]
         errorcode += ie;
      }
   }
 
   public static void main(String[] args) {
[I]// Not a foolproof check. But we want to make sure that there are two
// arguments on the command line.[/I]
      if (args.length < 2) {
         System.out.println("Usage: java RetrieveImage URLtoGet filename");
 
         System.exit(1);
      }
 
[I]// Retrieve the bytes from the URL.[/I]
      byte[] bytes = getURL(args[0]);
 
[I]// Store the bytes in the file.[/I]
      store(args[1],bytes);
 
[I]// If the errorcode is still the empty String, then there was no
// exceptional behavior in either method.[/I]
      if (errorcode.equals(""))
         System.out.println("The contents of " + args[0] + " were stored in " + args[1] + ".");
   }
 
}

You can try it with

java RetrieveImage <a href="http://www.pparc.ac.uk/nw/planet.jpg" target="_blank" rel="nofollow">http://www.pparc.ac.uk/nw/planet.jpg</a> planet.jpg

[Jim Yingst]

"Kyle", please take a look at our display name policy and then edit your display name to one less obviously fictitious (to some of us, at least.). Thank you.

[Jeff Albertson]

I don't agree with all that Keith wrote here -- buffering both input and output, then providing additional buffers and copying over and over again, but take a look at the code for copying from one file to another, from the Java Almanac::

void copy(File src, File dst) throws IOException {
    InputStream in = new FileInputStream(src);
    OutputStream out = new FileOutputStream(dst);
    
    byte[] buf = new byte[1024];
    int len;
    while ((len = in.read(buf)) > 0) {
        out.write(buf, 0, len);
    }
    in.close();
    out.close();
}

(I think you could do better by closing the streams in a finally block.) Given that url.openStream() returns an InputStream, all that needs to be added is q.e.d.

[Joe Ess]

If you already have an instance of BufferedImage, you can save it directly with the static write() method of javax.imageio.ImageIO

[Jeff Albertson]

Originally posted by Joe Ess:
If you already have an instance of BufferedImage, you can save it directly with the static write() method of javax.imageio.ImageIO

I think what the OP really wanted to do was copy from www.acme.com/coyote.gif to a local file xxx.gif. Converting the file back and forth to a BufferedImage is asking for trouble (apart from efficiency questions) -- what if you want to preserve the file's image format (woops, where's my gif writer?) and compression level, if any? Did you copy the file's metadata? Etc, etc...