Allow LogLevel to be used easily with commons logging

Add a `LogLevel.log` method that can be used to log a message at
the given level using commons logging.

Closes gh-35024

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.logging;
 
+import org.apache.commons.logging.Log;
+
 /**
  * Logging levels supported by a {@link LoggingSystem}.
  *
@@ -24,6 +26,54 @@ package org.springframework.boot.logging;
  */
 public enum LogLevel {
 
-	TRACE, DEBUG, INFO, WARN, ERROR, FATAL, OFF
+	TRACE(Log::trace),
+
+	DEBUG(Log::debug),
+
+	INFO(Log::info),
+
+	WARN(Log::warn),
+
+	ERROR(Log::error),
+
+	FATAL(Log::fatal),
+
+	OFF(null);
+
+	private final LogMethod logMethod;
+
+	LogLevel(LogMethod logMethod) {
+		this.logMethod = logMethod;
+	}
+
+	/**
+	 * Log a message to the given logger at this level.
+	 * @param logger the logger
+	 * @param message the message to log
+	 * @since 3.1.0
+	 */
+	public void log(Log logger, Object message) {
+		log(logger, message, null);
+	}
+
+	/**
+	 * Log a message to the given logger at this level.
+	 * @param logger the logger
+	 * @param message the message to log
+	 * @param cause the cause to log
+	 * @since 3.1.0
+	 */
+	public void log(Log logger, Object message, Throwable cause) {
+		if (logger != null && this.logMethod != null) {
+			this.logMethod.log(logger, message, cause);
+		}
+	}
+
+	@FunctionalInterface
+	private interface LogMethod {
+
+		void log(Log logger, Object message, Throwable cause);
+
+	}
 
 }

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

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2012-2023 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.apache.commons.logging.Log;
+import org.junit.jupiter.api.Test;
+
+import static org.mockito.BDDMockito.then;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Tests for {@link LogLevel}.
+ *
+ * @author Phillip Webb
+ */
+class LogLevelTests {
+
+	private Log logger = mock(Log.class);
+
+	private Exception exception = new Exception();
+
+	@Test
+	void logWhenTraceLogsAtTrace() {
+		LogLevel.TRACE.log(this.logger, "test");
+		LogLevel.TRACE.log(this.logger, "test", this.exception);
+		then(this.logger).should().trace("test", null);
+		then(this.logger).should().trace("test", this.exception);
+	}
+
+	@Test
+	void logWhenDebugLogsAtDebug() {
+		LogLevel.DEBUG.log(this.logger, "test");
+		LogLevel.DEBUG.log(this.logger, "test", this.exception);
+		then(this.logger).should().debug("test", null);
+		then(this.logger).should().debug("test", this.exception);
+	}
+
+	@Test
+	void logWhenInfoLogsAtInfo() {
+		LogLevel.INFO.log(this.logger, "test");
+		LogLevel.INFO.log(this.logger, "test", this.exception);
+		then(this.logger).should().info("test", null);
+		then(this.logger).should().info("test", this.exception);
+	}
+
+	@Test
+	void logWhenWarnLogsAtWarn() {
+		LogLevel.WARN.log(this.logger, "test");
+		LogLevel.WARN.log(this.logger, "test", this.exception);
+		then(this.logger).should().warn("test", null);
+		then(this.logger).should().warn("test", this.exception);
+	}
+
+	@Test
+	void logWhenErrorLogsAtError() {
+		LogLevel.ERROR.log(this.logger, "test");
+		LogLevel.ERROR.log(this.logger, "test", this.exception);
+		then(this.logger).should().error("test", null);
+		then(this.logger).should().error("test", this.exception);
+	}
+
+	@Test
+	void logWhenFatalLogsAtFatal() {
+		LogLevel.FATAL.log(this.logger, "test");
+		LogLevel.FATAL.log(this.logger, "test", this.exception);
+		then(this.logger).should().fatal("test", null);
+		then(this.logger).should().fatal("test", this.exception);
+	}
+
+	@Test
+	void logWhenOffDoesNotLog() {
+		LogLevel.OFF.log(this.logger, "test");
+		LogLevel.OFF.log(this.logger, "test", this.exception);
+		then(this.logger).shouldHaveNoInteractions();
+	}
+
+}