Make logging system factory ordering more robust

Closes gh-44689

Author: wilkinsona

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -176,7 +176,7 @@ public void cleanUp() {
 	/**
 	 * {@link LoggingSystemFactory} that returns {@link JavaLoggingSystem} if possible.
 	 */
-	@Order(Ordered.LOWEST_PRECEDENCE)
+	@Order(Ordered.LOWEST_PRECEDENCE - 1024)
 	public static class Factory implements LoggingSystemFactory {
 
 		private static final boolean PRESENT = ClassUtils.isPresent("java.util.logging.LogManager",

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java

@@ -63,7 +63,6 @@
 import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.logging.LoggingSystemFactory;
 import org.springframework.core.Conventions;
-import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
 import org.springframework.core.env.Environment;
 import org.springframework.core.io.Resource;
@@ -494,7 +493,7 @@ public static Environment getEnvironment(LoggerContext loggerContext) {
 	/**
 	 * {@link LoggingSystemFactory} that returns {@link Log4J2LoggingSystem} if possible.
 	 */
-	@Order(Ordered.LOWEST_PRECEDENCE)
+	@Order(0)
 	public static class Factory implements LoggingSystemFactory {
 
 		private static final boolean PRESENT = ClassUtils

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -483,7 +483,7 @@ void setStatusPrinterStream(PrintStream stream) {
 	/**
 	 * {@link LoggingSystemFactory} that returns {@link LogbackLoggingSystem} if possible.
 	 */
-	@Order(Ordered.LOWEST_PRECEDENCE)
+	@Order(Ordered.HIGHEST_PRECEDENCE + 1024)
 	public static class Factory implements LoggingSystemFactory {
 
 		private static final boolean PRESENT = ClassUtils.isPresent("ch.qos.logback.classic.LoggerContext",

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -20,7 +20,10 @@
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.logging.LoggingSystem.NoOpLoggingSystem;
+import org.springframework.boot.logging.java.JavaLoggingSystem;
+import org.springframework.boot.logging.log4j2.Log4J2LoggingSystem;
 import org.springframework.boot.logging.logback.LogbackLoggingSystem;
+import org.springframework.boot.testsupport.classpath.ClassPathExclusions;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
@@ -42,6 +45,18 @@ void logbackIsTheDefaultLoggingSystem() {
 		assertThat(LoggingSystem.get(getClass().getClassLoader())).isInstanceOf(LogbackLoggingSystem.class);
 	}
 
+	@Test
+	@ClassPathExclusions("logback-*.jar")
+	void log4j2IsUsedInTheAbsenceOfLogback() {
+		assertThat(LoggingSystem.get(getClass().getClassLoader())).isInstanceOf(Log4J2LoggingSystem.class);
+	}
+
+	@Test
+	@ClassPathExclusions({ "logback-*.jar", "log4j-*.jar" })
+	void julIsUsedInTheAbsenceOfLogbackAndLog4j2() {
+		assertThat(LoggingSystem.get(getClass().getClassLoader())).isInstanceOf(JavaLoggingSystem.class);
+	}
+
 	@Test
 	void loggingSystemCanBeDisabled() {
 		System.setProperty(LoggingSystem.SYSTEM_PROPERTY, LoggingSystem.NONE);