Support instantiating Kotlin classes with optional parameters

This commit updates BeanUtils class in order to add Kotlin optional
parameters with default values support to the immutable data classes
support introduced by SPR-15199.

Issue: SPR-15673

spring-webmvc/src/test/kotlin/org/springframework/web/servlet/mvc/method/annotation/ServletAnnotationControllerHandlerMethodKotlinTests.kt

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2002-2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.servlet.mvc.method.annotation
+
+import org.junit.Assert.*
+import org.junit.Test
+import org.springframework.mock.web.test.MockHttpServletRequest
+import org.springframework.mock.web.test.MockHttpServletResponse
+import org.springframework.web.bind.annotation.RequestMapping
+import org.springframework.web.bind.annotation.RestController
+
+/**
+ * @author Sebastien Deleuze
+ */
+class ServletAnnotationControllerHandlerMethodKotlinTests : AbstractServletHandlerMethodTests() {
+
+	@Test
+	fun dataClassBinding() {
+		initServletWithControllers(DataClassController::class.java)
+
+		val request = MockHttpServletRequest("GET", "/bind")
+		request.addParameter("param1", "value1")
+		request.addParameter("param2", "2")
+		val response = MockHttpServletResponse()
+		servlet.service(request, response)
+		assertEquals("value1-2", response.contentAsString)
+	}
+
+	@Test
+	fun dataClassBindingWithOptionalParameterAndAllParameters() {
+		initServletWithControllers(DataClassController::class.java)
+
+		val request = MockHttpServletRequest("GET", "/bind-optional-parameter")
+		request.addParameter("param1", "value1")
+		request.addParameter("param2", "2")
+		val response = MockHttpServletResponse()
+		servlet.service(request, response)
+		assertEquals("value1-2", response.contentAsString)
+	}
+
+	@Test
+	fun dataClassBindingWithOptionalParameterAndOnlyMissingParameters() {
+		initServletWithControllers(DataClassController::class.java)
+
+		val request = MockHttpServletRequest("GET", "/bind-optional-parameter")
+		request.addParameter("param1", "value1")
+		val response = MockHttpServletResponse()
+		servlet.service(request, response)
+		assertEquals("value1-12", response.contentAsString)
+	}
+
+
+	data class DataClass(val param1: String, val param2: Int)
+
+	data class DataClassWithOptionalParameter(val param1: String, val param2: Int = 12)
+
+	@RestController
+	class DataClassController {
+
+		@RequestMapping("/bind")
+		fun handle(data: DataClass) = "${data.param1}-${data.param2}"
+
+		@RequestMapping("/bind-optional-parameter")
+		fun handle(data: DataClassWithOptionalParameter) = "${data.param1}-${data.param2}"
+	}
+
+}