Sunday, March 11, 2012

Getting A File"s Mime Type In Java


I was just wondering how most people fetch a mime type from a file in Java? So far I've tried two utils: JMimeMagic & Mime-Util. The first gave me memory exceptions, the second doesn't close its streams off properly. I was just wondering if anyone else had a method/library that they used and worked correctly?


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5 comments:

  1. UserMarch 11, 2012 at 10:10 PM

    Getting A File’s Mime Type In Java

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  2. UserMarch 11, 2012 at 10:10 PM

    Unfortunately,

    mimeType = file.toURL().openConnection().getContentType();


    does not work, since this use of URL leaves a file locked, so that, for example, it is undeletable.

    However, you have this:

    mimeType= URLConnection.guessContentTypeFromName(file.getName());


    and also the following, which has the advantage of going beyond mere use of file extension, and takes a peek at content

    InputStream is = new BufferedInputStream(new FileInputStream(file));
    mimeType = URLConnection.guessContentTypeFromStream(is);
    //...close stream


    However, as suggested by the comment above, the built-in table of mime-types is quite limited, not including, for example, MSWord and PDF. So, if you want to generalize, you'll need to go beyond the built-in libraries, using, e.g., Mime-Util (which is a great library, using both file extension and content).

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  3. UserMarch 11, 2012 at 10:10 PM

    The JAF API is part of JDK 6. Look at javax.activation package.

    Most interesting classes are javax.activation.MimeType - an actual MIME type holder - and javax.activation.MimetypesFileTypeMap - class whose instance can resolve MIME type as String for a file:

    String fileName = "/path/to/file";
    MimetypesFileTypeMap mimeTypesMap = new MimetypesFileTypeMap();

    // only by file name
    String mimeType = mimeTypesMap.getContentType(fileName);

    // or by actual File instance
    File file = new File(fileName);
    mimeType = mimeTypesMap.getContentType(file);

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  4. UserMarch 11, 2012 at 10:10 PM

    I know this is solved, but just a heads up that in Java 7 you can now just use probeContentType: http://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#probeContentType(java.nio.file.Path)

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  5. UserMarch 11, 2012 at 10:10 PM

    From roseindia:

    FileNameMap fileNameMap = URLConnection.getFileNameMap();
    String mimeType = fileNameMap.getContentTypeFor("alert.gif");

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