Merge pull request #24717 from bono007

* pr/24717:
  Polish "Add support for GET requests for /actuator/startup"
  Add support for GET requests for /actuator/startup

Closes gh-24717

spring-boot-project/spring-boot-actuator-autoconfigure/src/docs/asciidoc/endpoints/startup.adoc

@@ -4,24 +4,38 @@
 The `startup` endpoint provides information about the application's startup sequence.
 
 
-
 [[startup-retrieving]]
 == Retrieving the Application Startup steps
 
-To retrieve the steps recorded so far during the application startup phase , make a `POST` request to `/actuator/startup`, as shown in the following curl-based example:
+The application startup steps can either be retrieved as a snapshot (`GET`) or drained from the buffer (`POST`).
 
-include::{snippets}/startup/curl-request.adoc[]
+[[startup-retrieving-snapshot]]
+=== Retrieving a snapshot of the Application Startup steps
+
+To retrieve the steps recorded so far during the application startup phase , make a `GET` request to `/actuator/startup`, as shown in the following curl-based example:
+
+include::{snippets}/startup-snapshot/curl-request.adoc[]
 
 The resulting response is similar to the following:
 
-include::{snippets}/startup/http-response.adoc[]
+include::{snippets}/startup-snapshot/http-response.adoc[]
+
 
+[[startup-retrieving-drain]]
+== Draining the Application Startup steps
 
+To drain and return the steps recorded so far during the application startup phase , make a `POST` request to `/actuator/startup`, as shown in the following curl-based example:
+
+include::{snippets}/startup/curl-request.adoc[]
+
+The resulting response is similar to the following:
+
+include::{snippets}/startup/http-response.adoc[]
 
 [[startup-retrieving-response-structure]]
 === Response Structure
 
-The response contains details of the application startup steps recorded so far by the application.
+The response contains details of the application startup steps.
 The following table describes the structure of the response:
 
 [cols="2,1,3"]

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/documentation/StartupEndpointDocumentationTests.java

@@ -26,12 +26,13 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
 import org.springframework.core.metrics.StartupStep;
+import org.springframework.restdocs.payload.FieldDescriptor;
 import org.springframework.restdocs.payload.JsonFieldType;
-import org.springframework.restdocs.payload.ResponseFieldsSnippet;
+import org.springframework.restdocs.payload.PayloadDocumentation;
 
 import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
 import static org.springframework.restdocs.payload.PayloadDocumentation.fieldWithPath;
-import static org.springframework.restdocs.payload.PayloadDocumentation.responseFields;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
@@ -39,6 +40,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
  * Tests for generating documentation describing {@link StartupEndpoint}.
  *
  * @author Brian Clozel
+ * @author Stephane Nicoll
  */
 class StartupEndpointDocumentationTests extends MockMvcEndpointDocumentationTests {
 
@@ -53,9 +55,20 @@ class StartupEndpointDocumentationTests extends MockMvcEndpointDocumentationTest
 		instantiate.end();
 	}
 
+	@Test
+	void startupSnapshot() throws Exception {
+		this.mockMvc.perform(get("/actuator/startup")).andExpect(status().isOk())
+				.andDo(document("startup-snapshot", PayloadDocumentation.responseFields(responseFields())));
+	}
+
 	@Test
 	void startup() throws Exception {
-		ResponseFieldsSnippet responseFields = responseFields(
+		this.mockMvc.perform(post("/actuator/startup")).andExpect(status().isOk())
+				.andDo(document("startup", PayloadDocumentation.responseFields(responseFields())));
+	}
+
+	private FieldDescriptor[] responseFields() {
+		return new FieldDescriptor[] {
 				fieldWithPath("springBootVersion").type(JsonFieldType.STRING)
 						.description("Spring Boot version for this application.").optional(),
 				fieldWithPath("timeline.startTime").description("Start time of the application."),
@@ -73,10 +86,7 @@ class StartupEndpointDocumentationTests extends MockMvcEndpointDocumentationTest
 				fieldWithPath("timeline.events.[].startupStep.tags[].key")
 						.description("The key of the StartupStep Tag."),
 				fieldWithPath("timeline.events.[].startupStep.tags[].value")
-						.description("The value of the StartupStep Tag."));
-
-		this.mockMvc.perform(post("/actuator/startup")).andExpect(status().isOk())
-				.andDo(document("startup", responseFields));
+						.description("The value of the StartupStep Tag.") };
 	}
 
 	@Configuration(proxyBeanMethods = false)

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/startup/StartupEndpoint.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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 +18,7 @@ package org.springframework.boot.actuate.startup;
 
 import org.springframework.boot.SpringBootVersion;
 import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
+import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
 import org.springframework.boot.actuate.endpoint.annotation.WriteOperation;
 import org.springframework.boot.context.metrics.buffering.BufferingApplicationStartup;
 import org.springframework.boot.context.metrics.buffering.StartupTimeline;
@@ -28,6 +29,7 @@ import org.springframework.boot.context.metrics.buffering.StartupTimeline;
  * application startup}.
  *
  * @author Brian Clozel
+ * @author Chris Bono
  * @since 2.4.0
  */
 @Endpoint(id = "startup")
@@ -44,6 +46,12 @@ public class StartupEndpoint {
 		this.applicationStartup = applicationStartup;
 	}
 
+	@ReadOperation
+	public StartupResponse startupSnapshot() {
+		StartupTimeline startupTimeline = this.applicationStartup.getBufferedTimeline();
+		return new StartupResponse(startupTimeline);
+	}
+
 	@WriteOperation
 	public StartupResponse startup() {
 		StartupTimeline startupTimeline = this.applicationStartup.drainBufferedTimeline();

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/startup/StartupEndpointTests.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -16,13 +16,17 @@
 
 package org.springframework.boot.actuate.startup;
 
+import java.util.function.Consumer;
+
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.SpringBootVersion;
+import org.springframework.boot.actuate.startup.StartupEndpoint.StartupResponse;
 import org.springframework.boot.context.metrics.buffering.BufferingApplicationStartup;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.metrics.ApplicationStartup;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -30,17 +34,15 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link StartupEndpoint}.
  *
  * @author Brian Clozel
+ * @author Chris Bono
  */
 class StartupEndpointTests {
 
 	@Test
 	void startupEventsAreFound() {
 		BufferingApplicationStartup applicationStartup = new BufferingApplicationStartup(256);
-		ApplicationContextRunner contextRunner = new ApplicationContextRunner()
-				.withInitializer((context) -> context.setApplicationStartup(applicationStartup))
-				.withUserConfiguration(EndpointConfiguration.class);
-		contextRunner.run((context) -> {
-			StartupEndpoint.StartupResponse startup = context.getBean(StartupEndpoint.class).startup();
+		testStartupEndpoint(applicationStartup, (startupEndpoint) -> {
+			StartupResponse startup = startupEndpoint.startup();
 			assertThat(startup.getSpringBootVersion()).isEqualTo(SpringBootVersion.getVersion());
 			assertThat(startup.getTimeline().getStartTime())
 					.isEqualTo(applicationStartup.getBufferedTimeline().getStartTime());
@@ -48,15 +50,32 @@ class StartupEndpointTests {
 	}
 
 	@Test
-	void bufferIsDrained() {
+	void bufferWithGetIsNotDrained() {
+		BufferingApplicationStartup applicationStartup = new BufferingApplicationStartup(256);
+		testStartupEndpoint(applicationStartup, (startupEndpoint) -> {
+			StartupResponse startup = startupEndpoint.startupSnapshot();
+			assertThat(startup.getTimeline().getEvents()).isNotEmpty();
+			assertThat(applicationStartup.getBufferedTimeline().getEvents()).isNotEmpty();
+		});
+	}
+
+	@Test
+	void bufferWithPostIsDrained() {
 		BufferingApplicationStartup applicationStartup = new BufferingApplicationStartup(256);
+		testStartupEndpoint(applicationStartup, (startupEndpoint) -> {
+			StartupResponse startup = startupEndpoint.startup();
+			assertThat(startup.getTimeline().getEvents()).isNotEmpty();
+			assertThat(applicationStartup.getBufferedTimeline().getEvents()).isEmpty();
+		});
+	}
+
+	private void testStartupEndpoint(ApplicationStartup applicationStartup, Consumer<StartupEndpoint> startupEndpoint) {
 		ApplicationContextRunner contextRunner = new ApplicationContextRunner()
 				.withInitializer((context) -> context.setApplicationStartup(applicationStartup))
 				.withUserConfiguration(EndpointConfiguration.class);
 		contextRunner.run((context) -> {
-			StartupEndpoint.StartupResponse startup = context.getBean(StartupEndpoint.class).startup();
-			assertThat(startup.getTimeline().getEvents()).isNotEmpty();
-			assertThat(applicationStartup.getBufferedTimeline().getEvents()).isEmpty();
+			assertThat(context).hasSingleBean(StartupEndpoint.class);
+			startupEndpoint.accept(context.getBean(StartupEndpoint.class));
 		});
 	}