How to detect invalid image URL (I mean image is not describe) with JAVA?

Question

I have a method to download image from URL. As like below..

public static byte[] downloadImageFromURL(final String strUrl) {
    InputStream in;
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    try {
        URL url = new URL(strUrl);
        in = new BufferedInputStream(url.openStream());
        byte[] buf = new byte[2048];
        int n = 0;
        while (-1 != (n = in.read(buf))) {
            out.write(buf, 0, n);
        }
        out.close();
        in.close();
    }
    catch (IOException e) {
        return null;
    }
    return out.toByteArray();
}

I have an image url and it is valid. for example.

https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTxfYM-hnD-Z80tgWdIgQKchKe-MXVUfTpCw1R5KkfJlbRbgr3Zcg

My problem is I don't want to download if image is really not exists.Like ....

https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTxfYM-hnD-Z80tgWdIgQKchKe-MXVUfTpCw1R5KkfJlbRbgr3Zcgaaaaabbbbdddddddddddddddddddddddddddd

This image shouldn't be download by my method. So , how can I know the giving image URL is not really exists. I don't want to validate my URL (I think that may not my solution ).

So, I googled for that. From this article ... How to check if a URL exists or returns 404 with Java? and Check if file exists on remote server using its URL

But this con.getResponseCode() will always return status code "200". This mean my method will also download invalid image urls. So , I output my bufferStream as like...

System.out.println(in.read(buf));

Invalid image URL produces "43". So , I add these lines of codes in my method.

    if (in.read(buf) == 43) {
       return null;
    }

It is ok. But I don't think that will always satisfy. Has another way to get it ? am I right? I would really appreciate any suggestions. This problem may struct my head. Thanks for reading my question.

*UPDATE

I call this download method and save downloaded image in some directory as..

            // call method to save image
            FileSupport.saveFile(filePath+".JPG", data);

After that I tried to output as...

            File file = new File(filePath+".JPG);
            System.err.println(file.length());

that may also produces "43" for invalid image urls. I want to know why that return "43" for all of invalid urls. what is "43" ?

Answer 1

Try this,

Open an image in notepad or something and check the first 3-4 characters, it will tell you the format of the image..

When downloading check the first 3 or 4 characters, that should tell you if this image is valid or not.

Note: Here, I'm assuming that your requirement is specific to certain types of images and not all possible images.

some samples:

‰PNG for PNG images ����JFIF for JPG images.

byte[] tenBytes=new byte[10];
// fill this array with the first 10 bytes.
String str = new String(tenBytes);
if(str.contains("JIFF")){
// JPG
}
if(str.contains("PNG"){
// PNG
} ...

if nothing matches, its either an invalid image or an image you don't want.

Note this is untested code.. you might have to make adjustments for it to work properly. you should look at this as an psuedo code to build your implementation...

Update: Instead of checking for file size 43, you should be looking for the content (as described above).

Answer 2

If

con.setRequestMethod("HEAD");

does not help you, you should do something like this (read from connection's input strean will fail if the image does not exist.

  HttpUrlConnection con = (HttpUrlConnection)url.openConnection;
  con.setRequestMethod("GET");
  con.addRequestProperty("User-Agent", "Mozilla/4.0");

  int responseCode = con.getResponseCode(); //if you do not get 200 here, you can stop

  if(responseCode != HttpUrlConnection.HTTP_OK) {
    return;
  }
  // Now, read image buffer
  byte[] image = null;

  try{

       InputStream in = new BufferedInputStream(con.getInputStream());
       ByteArrayOutputStream out = new ByteArrayOutputStream();
       byte[] buf = new byte[1024];

       int n = 0;

       while (-1!=(n=in.read(buf)))
       {
          out.write(buf, 0, n);
       }
       out.close();
       in.close();
       image = out.toByteArray();

    } catch (IOException ioe){
       // do whatever you need
    } finally {
       con.disconnect();
    }

Also, this code

 if (in.read(buf) == 43) {
       return null;
 }

does not look good. Some magic number, not clear what is it.

Answer 3

This is how I would do it:

//By Nishanth Chandradas

import java.awt.Image;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import javax.activation.MimetypesFileTypeMap;
import javax.swing.ImageIcon;

import java.io.File;

public class downloadimagefromurl {

    /**
     * @param args
     * @throws IOException 
     */

    public static byte[] downloadImageFromURL(final String strUrl) throws IOException {
        InputStream in;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        try {
            URL url = new URL(strUrl);
            in = new BufferedInputStream(url.openStream());
            byte[] buf = new byte[2048];
            int n = 0;
            while (-1 != (n = in.read(buf))) {
                out.write(buf, 0, n);
            }
            out.close();
            in.close();
        }
        catch (IOException e) {
            return null;
        }
        byte[] response = out.toByteArray();
        FileOutputStream fos = new FileOutputStream("/Users/Nish/Desktop/image.jpg");
        fos.write(response);
        fos.close();
        return response;
    }

    static boolean isImage(String image_path){
          Image image = new ImageIcon(image_path).getImage();
          if(image.getWidth(null) == -1){
                return false;
          }
          else{
                return true;
          }
        }

    public static void main(String[] args) throws IOException {
        downloadImageFromURL("https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTxfYM-hnD-Z80tgWdIgQKchKe-MXVUfTpCw1R5KkfJlbRbgr3Zcg");
     System.out.println(isImage("/Users/Nish/Desktop/image.jpg"));
    }

The output will be true or false depending if the download was an image or not.

Answer 4

You can add a second catch statement to catch java.io.FileNotFoundException

catch (FileNotFoundException e) {
    // Failed
}