Add a requiredExchange extension to RestClient

Closes gh-34692

Author: sdeleuze

Diff for: spring-web/src/main/kotlin/org/springframework/web/client/RestClientExtensions.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -18,6 +18,8 @@ package org.springframework.web.client
 
 import org.springframework.core.ParameterizedTypeReference
 import org.springframework.http.ResponseEntity
+import org.springframework.web.client.RestClient.RequestHeadersSpec
+import org.springframework.web.client.RestClient.RequestHeadersSpec.ExchangeFunction
 
 /**
  * Extension for [RestClient.RequestBodySpec.body] providing a `bodyWithType<Foo>(...)` variant
@@ -51,6 +53,15 @@ inline fun <reified T : Any> RestClient.ResponseSpec.body(): T? =
 inline fun <reified T : Any> RestClient.ResponseSpec.requiredBody(): T =
     body(object : ParameterizedTypeReference<T>() {}) ?: throw NoSuchElementException("Response body is required")
 
+/**
+ * Extension for [RestClient.RequestHeadersSpec.exchange] providing a `requiredExchange(...)` variant with a
+ * non-nullable return value.
+ * @throws NoSuchElementException if there is no response value
+ * @since 6.2.6
+ */
+fun <T: Any> RequestHeadersSpec<*>.requiredExchange(exchangeFunction: ExchangeFunction<T>, close: Boolean = true): T =
+	exchange(exchangeFunction, close) ?: throw NoSuchElementException("Response value is required")
+
 /**
  * Extension for [RestClient.ResponseSpec.toEntity] providing a `toEntity<Foo>()` variant
  * leveraging Kotlin reified type parameters. This extension is not subject to type
@@ -60,4 +71,5 @@ inline fun <reified T : Any> RestClient.ResponseSpec.requiredBody(): T =
  * @since 6.1
  */
 inline fun <reified T : Any> RestClient.ResponseSpec.toEntity(): ResponseEntity<T> =
-	toEntity(object : ParameterizedTypeReference<T>() {})
+	toEntity(object : ParameterizedTypeReference<T>() {})
+

Diff for: spring-web/src/test/kotlin/org/springframework/web/client/RestClientExtensionsTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -19,9 +19,12 @@ package org.springframework.web.client
 import io.mockk.every
 import io.mockk.mockk
 import io.mockk.verify
+import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertThrows
 import org.springframework.core.ParameterizedTypeReference
+import org.springframework.http.HttpRequest
+import org.springframework.web.client.RestClient.RequestHeadersSpec
 
 /**
  * Mock object based tests for [RestClient] Kotlin extensions
@@ -59,6 +62,24 @@ class RestClientExtensionsTests {
 		assertThrows<NoSuchElementException> { responseSpec.requiredBody<Foo>() }
 	}
 
+	@Test
+	fun `RequestHeadersSpec#requiredExchange`() {
+		val foo = Foo()
+		every { requestBodySpec.exchange(any<RequestHeadersSpec.ExchangeFunction<Foo>>(), any()) } returns foo
+		val exchangeFunction: (HttpRequest, RequestHeadersSpec.ConvertibleClientHttpResponse) -> Foo? =
+			{ request, response -> foo }
+		val value = requestBodySpec.requiredExchange(exchangeFunction)
+		assertThat(value).isEqualTo(foo)
+	}
+
+	@Test
+	fun `RequestHeadersSpec#requiredExchange with null response throws NoSuchElementException`() {
+		every { requestBodySpec.exchange(any<RequestHeadersSpec.ExchangeFunction<Foo>>(), any()) } returns null
+		val exchangeFunction: (HttpRequest, RequestHeadersSpec.ConvertibleClientHttpResponse) -> Foo? =
+			{ request, response -> null }
+		assertThrows<NoSuchElementException> { requestBodySpec.requiredExchange(exchangeFunction) }
+	}
+
 	@Test
 	fun `ResponseSpec#toEntity with reified type parameters`() {
 		responseSpec.toEntity<List<Foo>>()