读取文件类型（MIME）在Java中返回null

Question

I'm editing a custom CSV importer that doesn't want to run on my system. My version of Java is: "1.8.0_171".

String contentType = Files.probeContentType(filePath);          
    //Should return "text/csv";
System.out.println("You have "+contentType+" type file.");
    //returns "You have null type file."

I've checked whether the file is accessible - it returns true.

System.out.println( "File is readable: " + Files.isReadable(filePath));
// returns: "File is readable: true"

What steps should I take next? I found some similar bugs:

https://bugs.java.com/view_bug.do?bug_id=JDK-7144997 https://bugs.openjdk.java.net/browse/JDK-8080369

I don't know whether they are related however.

UPDATE Updating Java to version "10.0.1" did not help.

UPDATE 2 Adding null to the list of allowed file types did work, however I consider this a HUGE hack, and this still needs resolving.

Answer 1

On Windows without any additional FileTypeDetector implementations installed Java will use default file type detector RegistryFileTypeDetector , which will return whatever has been associated with that extension on that particular machine, meaning whatever is under HKEY_CLASSES_ROOT\\.csv is returned.

If you want to enable some software to run consider installing custom FileTypeDetector on classpath via ServiceLoader mechanism or associating .csv with required value in registry.