Reduce reflection in LoggingSystem to make it more Graal-friendly

Closes gh-22594

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

@@ -19,11 +19,13 @@ package org.springframework.boot.logging;
 import java.lang.reflect.Constructor;
 import java.util.Collections;
 import java.util.EnumSet;
-import java.util.LinkedHashMap;
 import java.util.List;
-import java.util.Map;
 import java.util.Set;
+import java.util.function.Function;
 
+import org.springframework.boot.logging.java.JavaLoggingSystem;
+import org.springframework.boot.logging.log4j2.Log4J2LoggingSystem;
+import org.springframework.boot.logging.logback.LogbackLoggingSystem;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.StringUtils;
 
@@ -56,15 +58,24 @@ public abstract class LoggingSystem {
 	 */
 	public static final String ROOT_LOGGER_NAME = "ROOT";
 
-	private static final Map<String, String> SYSTEMS;
+	private static final Function<ClassLoader, LoggingSystem> SYSTEM_FACTORY;
 
 	static {
-		Map<String, String> systems = new LinkedHashMap<>();
+		ClassLoader classLoader = LoggingSystem.class.getClassLoader();
-		systems.put("ch.qos.logback.core.Appender", "org.springframework.boot.logging.logback.LogbackLoggingSystem");
+		if (ClassUtils.isPresent("ch.qos.logback.core.Appender", classLoader)) {
-		systems.put("org.apache.logging.log4j.core.impl.Log4jContextFactory",
+			SYSTEM_FACTORY = (cl) -> new LogbackLoggingSystem(cl);
-				"org.springframework.boot.logging.log4j2.Log4J2LoggingSystem");
+		}
-		systems.put("java.util.logging.LogManager", "org.springframework.boot.logging.java.JavaLoggingSystem");
+		else if (ClassUtils.isPresent("org.apache.logging.log4j.core.impl.Log4jContextFactory", classLoader)) {
-		SYSTEMS = Collections.unmodifiableMap(systems);
+			SYSTEM_FACTORY = (cl) -> new Log4J2LoggingSystem(cl);
+		}
+		else if (ClassUtils.isPresent("java.util.logging.LogManager", classLoader)) {
+			SYSTEM_FACTORY = (cl) -> new JavaLoggingSystem(cl);
+		}
+		else {
+			SYSTEM_FACTORY = (cl) -> {
+				throw new IllegalStateException("No suitable logging system located");
+			};
+		}
 	}
 
 	/**
@@ -155,9 +166,7 @@ public abstract class LoggingSystem {
 			}
 			return get(classLoader, loggingSystem);
 		}
-		return SYSTEMS.entrySet().stream().filter((entry) -> ClassUtils.isPresent(entry.getKey(), classLoader))
+		return SYSTEM_FACTORY.apply(classLoader);
-				.map((entry) -> get(classLoader, entry.getValue())).findFirst()
-				.orElseThrow(() -> new IllegalStateException("No suitable logging system located"));
 	}
 
 	private static LoggingSystem get(ClassLoader classLoader, String loggingSystemClass) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/LogbackAndLog4J2ExcludedLoggingSystemTests.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2012-2019 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;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.logging.java.JavaLoggingSystem;
+import org.springframework.boot.testsupport.classpath.ClassPathExclusions;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link LoggingSystem} when Logback is not on the classpath.
+ *
+ * @author Andy Wilkinson
+ */
+// Log4j2 is implicitly excluded due to LOG4J-2030
+@ClassPathExclusions("logback-*.jar")
+class LogbackAndLog4J2ExcludedLoggingSystemTests {
+
+	@Test
+	void whenLogbackAndLog4J2AreNotPresentJULIsTheLoggingSystem() {
+		assertThat(LoggingSystem.get(getClass().getClassLoader())).isInstanceOf(JavaLoggingSystem.class);
+	}
+
+}

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

@@ -20,6 +20,7 @@ import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.logging.LoggingSystem.NoOpLoggingSystem;
+import org.springframework.boot.logging.logback.LogbackLoggingSystem;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
@@ -36,6 +37,11 @@ class LoggingSystemTests {
 		System.clearProperty(LoggingSystem.SYSTEM_PROPERTY);
 	}
 
+	@Test
+	void logbackIsTheDefaultLoggingSystem() {
+		assertThat(LoggingSystem.get(getClass().getClassLoader())).isInstanceOf(LogbackLoggingSystem.class);
+	}
+
 	@Test
 	void loggingSystemCanBeDisabled() {
 		System.setProperty(LoggingSystem.SYSTEM_PROPERTY, LoggingSystem.NONE);