Transparently improve Java 7 mime-type recognition with Apache Tika

Java 7 comes with the method java.nio.file.Files#probeContentType(path) to determine the content type of a file at the given path. It returns a mime type identifier. The implementation actually looks at the file content and inspects so-called “magic” byte sequences, which is more reliable than just trusting filename extensions.

However, the default implementation included in Java 7 seems to be platform dependent and not very complete. For example, for me it did not even recognize an mp3 file as audio/mpeg. Fortunately, the Open Source library Apache Tika provides more comprehensive mime type detection and seems to be platform independent.

As shown below, you can register a simple Tika based FileTypeDetector implementation with the Java Service Provider Interface (SPI) to transparently enhance the behaviour of java.nio.file.Files#probeContentType(path). As soon as the resulting jar is in your classpath, the SPI mechanism wil pick up our implementation class and Files.probeContentType(..) will automatically use it behind the scenes.

Maven dependency

        <dependency>
            <groupId>org.apache.tika</groupId>
            <artifactId>tika-core</artifactId>
            <version>1.4</version>
        </dependency>

FileTypeDetector.java

package net.doepner.file;

import java.io.IOException;
import java.nio.file.Path;

import org.apache.tika.Tika;

/**
 * Detects the mime type of files (ideally based on marker in file content)
 */
public class FileTypeDetector extends java.nio.file.spi.FileTypeDetector {

    private final Tika tika = new Tika();

    @Override
    public String probeContentType(Path path) throws IOException {
        return tika.detect(path.toFile());
    }
}

Service Provider registration

To register the implementation with the Java Service Provider Interface (SPI), you need to have a plaintext file /META-INF/services/java.nio.file.spi.FileTypeDetector in the same jar that contains the class net.doepner.file.FileTypeDetector. The text file contains just one line with the fully qualified name of the implementing class:

net.doepner.file.FileTypeDetector

With Maven, you simply create the file src/main/resources/META-INF/services/java.nio.file.spi.FileTypeDetector containing the line shown above.

See the ServiceLoader documentation for details about Java SPI.

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