Add ClasspathFileUtil for easy getting files from resource directory

spring-core/src/main/kotlin/org/springframework/util/ResourceClasspathFileUtil.kt

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+package org.springframework.util
+
+import java.io.File
+
+/**
+ * Class for reading files from classpath without defining classpath directory.
+ * E.g. you can load json files from classpath easily with this class.
+ * @param resourcePath path to resource in classpath.
+ *
+ * @author Alexander Ilinykh
+ */
+class ResourceClasspathFileUtil(resourcePath: String) :
+	File(ResourceClasspathFileUtil::class.java.classLoader.getResource(resourcePath)!!.toURI())

spring-core/src/test/kotlin/org/springframework/util/ResourceClasspathFileUtilTest.kt

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+package org.springframework.util
+
+import org.assertj.core.api.Assertions
+import org.junit.jupiter.api.Test
+
+class ResourceClasspathFileUtilTest {
+
+	@Test
+	fun correctReadFromClasspath() {
+		val file = ResourceClasspathFileUtil("org/springframework/util/classpathfileutildata.txt")
+		Assertions.assertThat(file.readText()).isEqualTo("Hello Spring!")
+	}
+}

spring-core/src/test/resources/org/springframework/util/classpathfileutildata.txt

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+Hello Spring!