Kotlin simple mimetype/file extension detector

mime-type-catalog.csv

MimeTypeDetector.kt

import org.slf4j.LoggerFactory

class MimeTypeDetector private constructor() {

    private val log = LoggerFactory.getLogger(MimeTypeDetector::class.java)
    private var extensionToMimeTypeMapping: MutableMap<String, String> = mutableMapOf()
    private var mimeTypeToExtensionMapping: MutableMap<String, String> = mutableMapOf()

    companion object {

        private var detector: MimeTypeDetector? = null

        fun getInstance(): MimeTypeDetector {
            if (detector == null) {
                detector = MimeTypeDetector()
            }
            return detector!!
        }
    }

    fun configure(extensionMimeTypePairs: Collection<Pair<String, String>>) {
        extensionMimeTypePairs.forEach { p ->
            extensionToMimeTypeMapping[p.first] = p.second
            mimeTypeToExtensionMapping[p.second] = p.first
        }
    }

    fun findExtension(mimeType: String): String? {
        if (mimeTypeToExtensionMapping.isEmpty()) {
            log.warn("Mime type to extension mapping is empty. Please configure it.")
        }
        return mimeTypeToExtensionMapping[mimeType]
    }

    fun findMimeType(extension: String): String? {
        if (mimeTypeToExtensionMapping.isEmpty()) {
            log.warn("Extension to mime type mapping is empty. Please configure it.")
        }
        return extensionToMimeTypeMapping[extension]
    }

}

MimeTypeDetectorBootstrap.kt

import java.io.File

fun main(args : Array<String>) { 
  val supportedMimeTypes: MutableCollection<Pair<String, String>> = mutableListOf()
  val mimeTypeCatalog = File("mime-type-catalog.csv")
  assert(mimeTypeCatalog.exists())
  mimeTypeCatalog.file.forEachLine { l ->
      val tokens = l.split(",")
      supportedMimeTypes.add(Pair(tokens.first(), tokens.last()))
  }

  MimeTypeDetector.getInstance().configure(supportedMimeTypes)
}

No strings-attached kotlin file extension to mime-type detector / mime-type to file extension detector. It's no replacement for a solution like apache tika, but for simple use cases works.