How can I get MIME type of an InputStream of a file that is being uploaded?

Question

Simple question: how can I get MIME type (or content type) of an InputStream, without saving file, for a file that a user is uploading to my servlet?

Answer 1

I wrote my own content-type detector for a byte[] because the libraries above weren't suitable or I didn't have access to them. Hopefully this helps someone out.

// retrieve file as byte[] byte[] b = odHit.retrieve( "" );  // copy top 32 bytes and pass to the guessMimeType(byte[]) funciton byte[] topOfStream = new byte[32]; System.arraycopy(b, 0, topOfStream, 0, topOfStream.length); String mimeGuess = guessMimeType(topOfStream); 

...

private static String guessMimeType(byte[] topOfStream) {      String mimeType = null;     Properties magicmimes = new Properties();     FileInputStream in = null;      // Read in the magicmimes.properties file (e.g. of file listed below)     try {         in = new FileInputStream( "magicmimes.properties" );         magicmimes.load(in);         in.close();     } catch (FileNotFoundException e) {         e.printStackTrace();     } catch (IOException e) {         e.printStackTrace();     }      // loop over each file signature, if a match is found, return mime type     for ( Enumeration keys = magicmimes.keys(); keys.hasMoreElements(); ) {         String key = (String) keys.nextElement();         byte[] sample = new byte[key.length()];         System.arraycopy(topOfStream, 0, sample, 0, sample.length);         if( key.equals( new String(sample) )){             mimeType = magicmimes.getProperty(key);             System.out.println("Mime Found! "+ mimeType);             break;         } else {             System.out.println("trying "+key+" == "+new String(sample));         }     }      return mimeType; } 

magicmimes.properties file example (not sure these signatures are correct, but they worked for my uses)

# SignatureKey                  content/type \u0000\u201E\u00f1\u00d9        text/plain \u0025\u0050\u0044\u0046        application/pdf %PDF                            application/pdf \u0042\u004d                    image/bmp GIF8                            image/gif \u0047\u0049\u0046\u0038        image/gif \u0049\u0049\u004D\u004D        image/tiff \u0089\u0050\u004e\u0047        image/png \u00ff\u00d8\u00ff\u00e0        image/jpg