Disable Log4j2's shutdown hook with 2.18 and later

Closes gh-31719

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/SpringBootPropertySource.java

@@ -51,4 +51,14 @@ public class SpringBootPropertySource implements PropertySource {
 		return -200;
 	}
 
+	@Override
+	public String getProperty(String key) {
+		return this.properties.get(key);
+	}
+
+	@Override
+	public boolean containsProperty(String key) {
+		return this.properties.containsKey(key);
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/log4j2/SpringBootPropertySourceTests.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2012-2022 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.logging.log4j2;
+
+import java.util.stream.Stream;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.core.util.Constants;
+import org.apache.logging.log4j.core.util.ShutdownCallbackRegistry;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.testsupport.classpath.ClassPathExclusions;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link SpringBootPropertySource}.
+ *
+ * @author Andy Wilkinson
+ */
+@ClassPathExclusions({ "jakarta.servlet-api-*.jar", "tomcat-embed-core-*.jar" })
+class SpringBootPropertySourceTests {
+
+	@Test
+	void propertySourceHasDisabledShutdownHook() {
+		// Log4j2 disables the hook automatically in a web app so we check that it doesn't
+		// think it's in one
+		assertThat(Constants.IS_WEB_APP).isFalse();
+		assertThat(((ShutdownCallbackRegistry) LogManager.getFactory()).addShutdownCallback(() -> {
+		})).isNull();
+	}
+
+	@Test
+	void allDefaultMethodsAreImplemented() {
+		assertThat(Stream.of(SpringBootPropertySource.class.getMethods()).filter((method) -> method.isDefault()))
+				.isEmpty();
+	}
+
+}