Logback logging system does not process URLs with paths not ending in .xml

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -281,14 +281,9 @@ private void reportConfigurationErrorsIfNecessary(LoggerContext loggerContext) {
 
 	private void configureByResourceUrl(LoggingInitializationContext initializationContext, LoggerContext loggerContext,
 			URL url) throws JoranException {
-		if (url.getPath().endsWith(".xml")) {
-			JoranConfigurator configurator = new SpringBootJoranConfigurator(initializationContext);
-			configurator.setContext(loggerContext);
-			configurator.doConfigure(url);
-		}
-		else {
-			throw new IllegalArgumentException("Unsupported file extension in '" + url + "'. Only .xml is supported");
-		}
+		JoranConfigurator configurator = new SpringBootJoranConfigurator(initializationContext);
+		configurator.setContext(loggerContext);
+		configurator.doConfigure(url);
 	}
 
 	private void stopAndReset(LoggerContext loggerContext) {

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

@@ -37,6 +37,7 @@
 import ch.qos.logback.classic.spi.LoggerContextListener;
 import ch.qos.logback.core.ConsoleAppender;
 import ch.qos.logback.core.encoder.LayoutWrappingEncoder;
+import ch.qos.logback.core.joran.spi.JoranException;
 import ch.qos.logback.core.rolling.RollingFileAppender;
 import ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy;
 import ch.qos.logback.core.util.DynamicClassLoadingException;
@@ -832,8 +833,17 @@ void whenConfigLocationIsNotXmlThenIllegalArgumentExceptionShouldBeThrown() {
 		assertThatIllegalStateException()
 			.isThrownBy(() -> initialize(this.initializationContext, "classpath:logback-invalid-format.txt",
 					getLogFile(tmpDir() + "/tmp.log", null)))
-			.satisfies((ex) -> assertThat(ex.getCause()).isInstanceOf(IllegalArgumentException.class)
-				.hasMessageStartingWith("Unsupported file extension"));
+			.satisfies((ex) -> assertThat(ex.getCause()).isInstanceOf(JoranException.class)
+				.hasMessageStartingWith("Problem parsing XML document. See previously reported errors"));
+	}
+
+	@Test
+	void whenConfigLocationIsXmlFileWithoutExtensionShouldWork(CapturedOutput output) {
+		this.loggingSystem.beforeInitialize();
+		initialize(this.initializationContext, "classpath:logback-without-extension",
+				getLogFile(tmpDir() + "/tmp.log", null));
+		this.logger.info("No extension and works!");
+		assertThat(output.toString()).contains("No extension and works!");
 	}
 
 	@Test

spring-boot-project/spring-boot/src/test/resources/logback-without-extension

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+	<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
+		<encoder>
+			<pattern>%msg</pattern>
+		</encoder>
+	</appender>
+	<root level="INFO">
+		<appender-ref ref="CONSOLE" />
+	</root>
+</configuration>