Get actual file Content type after extension change - java

To identify the exact file content type, not go by extensions. Because there could be a scenario where file can be uploaded by changing the extesions.

eg: test.jpg file is renamed to test.jpg.txt - browser shows this file content type as text/plain. But the actual file is of image/jpeg.

This can be handled by below code:

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;

public class ActualContentType {
    public static void main(String[] args) throws Exception {

        Boolean status = isJPEG(new File("C:\\test.txt.jpg"));
        System.out.println("Status: " + status);
    }

    //http://www.filesignatures.net/index.php?page=search&search=FFD8FFE0&mode=SIG    

private static Boolean isJPEG(File filename) throws Exception {
        DataInputStream ins = new DataInputStream(new BufferedInputStream(new FileInputStream(filename)));
        try {
            if (ins.readInt() == 0xffd8ffe0) {
                return true;
            } else {
                return false;
            }
        } finally {
            ins.close();
        }
    }
}