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?
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