From b34c268547cd7920273eed4d4620fd62a8af45a9 Mon Sep 17 00:00:00 2001
From: im47cn <67424112+im47cn@users.noreply.github.com>
Date: Sun, 28 Jun 2020 10:41:10 +0800
Subject: [PATCH 1/2] Avoid NPE when binder is closed before started event

Previously, if TomcatMetricsBinder destroy() was called before it had
received an ApplicationStartedEvent an NPE would be thrown due to
TomcatMetrics being null. This NPE was then caught and logged at
warning level by the disposable bean adapter.

This prevents the NPE by checking that the TomcatMetrics instance is
null before calling close() on it.

See gh-22141
---
 .../boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java  | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java
index 688692ff79c..1e065eb4607 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java
@@ -86,7 +86,9 @@ public class TomcatMetricsBinder implements ApplicationListener<ApplicationStart
 
 	@Override
 	public void destroy() {
-		this.tomcatMetrics.close();
+		if (null != this.tomcatMetrics) {
+			this.tomcatMetrics.close();
+		}
 	}
 
 }

From 3922fb71649c7f3fa18ccc07f97aff7c8c3fec8c Mon Sep 17 00:00:00 2001
From: Andy Wilkinson <awilkinson@pivotal.io>
Date: Tue, 30 Jun 2020 13:26:30 +0100
Subject: [PATCH 2/2] Polish "Avoid NPE when binder is closed before started
 event"

See gh-22141
---
 .../web/tomcat/TomcatMetricsBinder.java       |  2 +-
 .../web/tomcat/TomcatMetricsBinderTests.java  | 38 +++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinderTests.java

diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java
index 1e065eb4607..38920b56c60 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinder.java
@@ -86,7 +86,7 @@ public class TomcatMetricsBinder implements ApplicationListener<ApplicationStart
 
 	@Override
 	public void destroy() {
-		if (null != this.tomcatMetrics) {
+		if (this.tomcatMetrics != null) {
 			this.tomcatMetrics.close();
 		}
 	}
diff --git a/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinderTests.java b/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinderTests.java
new file mode 100644
index 00000000000..fd7d43d640e
--- /dev/null
+++ b/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/tomcat/TomcatMetricsBinderTests.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.boot.actuate.metrics.web.tomcat;
+
+import io.micrometer.core.instrument.MeterRegistry;
+import org.junit.jupiter.api.Test;
+
+import static org.mockito.Mockito.mock;
+
+/**
+ * Tests for {@link TomcatMetricsBinder}.
+ *
+ * @author Andy Wilkinson
+ */
+class TomcatMetricsBinderTests {
+
+	private final MeterRegistry meterRegistry = mock(MeterRegistry.class);
+
+	@Test
+	void destroySucceedsWhenCalledBeforeApplicationHasStarted() {
+		new TomcatMetricsBinder(this.meterRegistry).destroy();
+	}
+
+}