Kotlin: get list of all files in resource folder - kotlin

Question

Is there a way to get list of all files in "resources" folder in Kotlin?
I can read specific file as
Application::class.java.getResourceAsStream("/folder/filename.ext")
But sometimes I just want to extract everything from folder "folder" to an external directory.

Answer 1

As I struggled with the same issue and couldn't find a concrete answer, so I had to write one myself.
Here is my solution:
fun getAllFilesInResources()
{
val projectDirAbsolutePath = Paths.get("").toAbsolutePath().toString()
val resourcesPath = Paths.get(projectDirAbsolutePath, "/src/main/resources")
val paths = Files.walk(resourcesPath)
.filter { item -> Files.isRegularFile(item) }
.filter { item -> item.toString().endsWith(".txt") }
.forEach { item -> println("filename: $item") }
}
Here I have parsed through all the files in the /src/main/resources folder and then filtered only the regular files (no directories included) and then filtered for the text files within the resources directory.
The output is a list of all the absolute file paths with the extension .txt in the resources folder. Now you can use these paths to copy the files to an external folder.

Answer 2

There are no methods for it (i.e. Application::class.java.listFilesInDirectory("/folder/")), but you can create your own system to list the files in a directory:
#Throws(IOException::class)
fun getResourceFiles(path: String): List<String> = getResourceAsStream(path).use{
return if(it == null) emptyList()
else BufferedReader(InputStreamReader(it)).readLines()
}
private fun getResourceAsStream(resource: String): InputStream? =
Thread.currentThread().contextClassLoader.getResourceAsStream(resource)
?: resource::class.java.getResourceAsStream(resource)
Then just call getResourceFiles("/folder/") and you'll get a list of files in the folder, assuming it's in the classpath.
This works because Kotlin has an extension function that reads lines into a List of Strings. The declaration is:
/**
* Reads this reader content as a list of lines.
*
* Do not use this function for huge files.
*/
public fun Reader.readLines(): List<String> {
val result = arrayListOf<String>()
forEachLine { result.add(it) }
return result
}

Answer 3

Two distinct parts:
Obtain a file that represents the resource directory
Traverse the directory
For 1 you can use Java's getResource:
val dir = File( object {}.javaClass.getResource(directoryPath).file )
For 2 you can use Kotlin's File.walk extension function that returns a sequence of files which you can process, e.g:
dir.walk().forEach { f ->
if(f.isFile) {
println("file ${f.name}")
} else {
println("dir ${f.name}")
}
}
Put together you may end up with the following code:
fun onEachResource(path: String, action: (File) -> Unit) {
fun resource2file(path: String): File {
val resourceURL = object {}.javaClass.getResource(path)
return File(checkNotNull(resourceURL, { "Path not found: '$path'" }).file)
}
with(resource2file(path)) {
this.walk().forEach { f -> action(f) }
}
}
so that if you have resources/nested direcory, you can:
fun main() {
val print = { f: File ->
when (f.isFile) {
true -> println("[F] ${f.absolutePath}")
false -> println("[D] ${f.absolutePath}")
}
}
onEachResource("/nested", print)
}

Answer 4

Here is a solution to iterate over JAR-packed resources on JVM:
fun iterateResources(resourceDir: String) {
val resource = MethodHandles.lookup().lookupClass().classLoader.getResource(resourceDir)
?: error("Resource $resourceDir was not found")
FileSystems.newFileSystem(resource.toURI(), emptyMap<String, String>()).use { fs ->
Files.walk(fs.getPath(resourceDir))
.filter { it.extension == "ttf" }
.forEach { file -> println(file.toUri().toString()) }
}
}

Answer 5

Here is a pretty simple solution that I found.
File("/path/to/file.txt")
// make an iterable file tree
.walk()
// only files no directories
.filter { it.isFile }
// last modified from top to bottom (most recent on top)
.sortedByDescending { it.lastModified() }
// do things on the files
.forEachIndexed {
i, it ->
// use the most recent file and delete the other ones
if (i == 0) {
useMe(it)
} else {
it.delete()
}
}