Get the Mime Type from a File

Using javax.activation.MimetypesFileTypeMap

activation.jar is required, it can be downloaded from http://java.sun.com/products/javabeans/glasgow/jaf.html.

The MimetypesFileMap class is used to map a File to a Mime Type. Mime types supported are defined in a ressource file inside the activation.jar.

import javax.activation.MimetypesFileTypeMap;
import java.io.File;

class GetMimeType {
  public static void main(String args[]) {
    File f = new File("gumby.gif");
    System.out.println("Mime Type of " + f.getName() + " is " +
                         new MimetypesFileTypeMap().getContentType(f));
    // expected output :
    // "Mime Type of gumby.gif is image/gif"
  }
}

The built-in mime-type list is very limited but a mechanism is available to add very easily more Mime Types/extensions.

The MimetypesFileTypeMap looks in various places in the user's system for MIME types file entries. When requests are made to search for MIME types in the MimetypesFileTypeMap, it searches MIME types files in the following order:

Programmatically added entries to the MimetypesFileTypeMap instance.
The file .mime.types in the user's home directory.
The file <java.home>/lib/mime.types.
The file or resources named META-INF/mime.types.
The file or resource named META-INF/mimetypes.default (usually found only in the activation.jar file).

This method is interesting when you need to deal with incoming files with the filenames normalized. The result is very fast because only the extension is used to guess the nature of a given file.

Using java.net.URL

Warning : this method is very slow!.

Like the above method a match is done with the extension. The mapping between the extension and the mime-type is defined in the file [jre_home]\lib\content-types.properties

import java.net.*;

public class FileUtils{
  public static String getMimeType(String fileUrl)
    throws java.io.IOException, MalformedURLException 
  {
    String type = null;
    URL u = new URL(fileUrl);
    URLConnection uc = null;
    uc = u.openConnection();
    type = uc.getContentType();
    return type;
  }

  public static void main(String args[]) throws Exception {
    System.out.println(FileUtils.getMimeType("file://c:/temp/test.TXT"));
    // output :  text/plain
  }
}

Using JMimeMagic

Checking the file extension is not a very strong way to determine the file type. A more robust solution is possible with the JMimeMagic library. JMimeMagic is a Java library (LGLP licence) that retrieves file and stream mime types by checking magic headers.

// snippet for JMimeMagic lib
//     http://sourceforge.net/projects/jmimemagic/

Magic parser = new Magic() ;
// getMagicMatch accepts Files or byte[], 
// which is nice if you want to test streams
MagicMatch match = parser.getMagicMatch(new File("gumby.gif"));
System.out.println(match.getMimeType()) ;

Thanks to Jean-Marc Autexier and sygsix for the tip!

Using mime-util

Another tool is mime-util. This tool can detect using the file extension or the magic header technique.

// snippet for mime-util lib
//     http://sourceforge.net/projects/mime-util

public static final String UNKNOWN_MIME_TYPE="application/x-unknown-mime-type";
...
String mimeType = MimeUtil.getMagicMimeType(file);
if(mimeType == null) mimeType = UNKNOWN_MIME_TYPE;

The nice thing about mime-util is that there is no dependency (with others Apache packages) so it is very lightweight.

Using Droid

DROID (Digital Record Object Identification) is a software tool to perform automated batch identification of file formats.

DROID uses internal and external signatures to identify and report the specific file format versions of digital files. These signatures are stored in an XML signature file, generated from information recorded in the PRONOM technical registry. New and updated signatures are regularly added to PRONOM, and DROID can be configured to automatically download updated signature files from the PRONOM website via web services.

It can be invoked from two interfaces, a Java Swing GUI or a command line interface.

http://droid.sourceforge.net/wiki/index.php/Introduction

Aperture framework

Aperture is an open source library and framework for crawling and indexing information sources such as file systems, websites and mail boxes.

The Aperture code consists of a number of related but independently usable parts:

Crawling of information sources: file systems, websites, mail boxes
MIME type identification
Full-text and metadata extraction of various file formats
Opening of crawled resources

For each of these parts, a set of APIs has been developed and a number of implementations is provided.

http://aperture.wiki.sourceforge.net/Overview