Kotlin读取文件问题

Question

I am trying to read a csv file using jackson but whenever I actually go to declare the file, i get the below exception:

IllegalStateException: classLoader.getResource("/src/integTest/testdata/Tests.csv") cannot be null

import com.fasterxml.jackson.databind.MappingIterator
import com.fasterxml.jackson.dataformat.csv.CsvMapper
import java.io.File

class CsvReader(private val fileName: String, private val testCase: TestCase) {

fun readCsv() {
    // configure schema and reader
    val mapper = CsvMapper()
    val schema = mapper.schemaFor(testCase.javaClass)
    val objectReader = mapper.readerFor(testCase.javaClass).with(schema)

//TODO this returns: java.lang.IllegalStateException: javaClass.getResource(fileName) must not be null
    val reader = File(javaClass.getResource(fileName).file).reader()

    //read file
    val mappingIterator: MappingIterator<TestCase> = objectReader.readValues(reader)
    while (mappingIterator.hasNext()) {
        //TODO get fields from read and return a TestCase Object
        println(mappingIterator.next())
    }
}

I am initializing the class using the following file path as a parameter:

var FILE_NAME: String = "/src/integTest/kotlin/testdata/testCase.csv"

Anyone else ever encountered this issue?

Answer 1

Gradle seemed to be looking for the file in a src/resources directory.

In addition kotlin didnt seem to play nicely with java so I added the Jackson Kotlin module

Played around with generics so the code could be reusable elsewhere. Seems to work nicely now.

Here is the new code:

import com.fasterxml.jackson.databind.MappingIterator
import com.fasterxml.jackson.dataformat.csv.CsvMapper
import com.fasterxml.jackson.dataformat.csv.CsvSchema
import com.fasterxml.jackson.module.kotlin.KotlinModule
import org.springframework.core.io.ClassPathResource


inline fun <reified T> readCsv(filename: String): List<T> {
    // configure mapper, schema and reader
    val mapper = CsvMapper().apply { registerModule(KotlinModule()) }
    val bootstrapSchema = CsvSchema.emptySchema().withHeader()
    val objectReader = mapper.readerFor(T::class.java).with(bootstrapSchema)

    //Read File and produce list from CSV
    ClassPathResource(filename).inputStream.use {
        val mappingIterator: MappingIterator<T> = objectReader.readValues(it)

        val items = mutableListOf<T>()

        mappingIterator.forEach { items.add(it) }

        return items.toList()
    }
}

Answer 2

File(javaClass.getResource(fileName).file).reader()

This is the problematic code. You are trying to read a resource as a file - but a resource is no file. It might be stored in your file system, it might be packaged inside a JAR file etc - this is why Java returns a URL instead of a File when you call Class.getResource .

Instead, you should be using the Class.getResourceAsStream method and convert that to a reader:

javaClass.getResourceAsStream(fileName)?.let { InputStreamReader(it) }

Note that getResourceAsStream might return null if the resource was not found.

Answer 3

The below code helps,

fun getResource(fileName: String): String {
    val clazzLoader = this::class.java.classLoader
    val stream = clazzLoader.getResourceAsStream(fileName)
    val reader = stream.bufferedReader()
    if (!Objects.isNull(reader)) {
        val data = reader.readText()
        reader.close()
        return data
    }
    throw RuntimeException("The requested file $fileName not found")
}