Add support for configuring Log4j2 rolling policy properties via application.properties, similar to Logback.

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

@@ -58,8 +58,10 @@
 import org.springframework.boot.logging.LoggingInitializationContext;
 import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.logging.LoggingSystemFactory;
+import org.springframework.boot.logging.LoggingSystemProperties;
 import org.springframework.core.Conventions;
 import org.springframework.core.annotation.Order;
+import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.Environment;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
@@ -128,6 +130,11 @@ public class Log4J2LoggingSystem extends AbstractLoggingSystem {
 		this.loggerContext = loggerContext;
 	}
 
+	@Override
+	public LoggingSystemProperties getSystemProperties(ConfigurableEnvironment environment) {
+		return new Log4J2LoggingSystemProperties(environment, getDefaultValueResolver(environment), null);
+	}
+
 	@Override
 	protected String[] getStandardConfigLocations() {
 		// With Log4J2 we use the ConfigurationFactory

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemProperties.java

@@ -0,0 +1,93 @@
+
+package org.springframework.boot.logging.log4j2;
+
+import java.util.function.BiConsumer;
+import java.util.function.Function;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.boot.logging.LogFile;
+import org.springframework.boot.logging.LoggingSystemProperties;
+import org.springframework.core.convert.ConversionFailedException;
+import org.springframework.core.convert.ConverterNotFoundException;
+import org.springframework.core.env.Environment;
+import org.springframework.core.env.PropertyResolver;
+import org.springframework.util.unit.DataSize;
+
+/**
+ * {@link Log4J2LoggingSystemProperties} for Log4j2.
+ *
+ * @see Log4J2RollingPolicySystemProperty
+ * @author Andrey Timonin
+ * @since 4.1.0
+ */
+public class Log4J2LoggingSystemProperties extends LoggingSystemProperties {
+
+	public Log4J2LoggingSystemProperties(Environment environment) {
+		super(environment);
+	}
+
+	/**
+	 * Create a new {@link Log4J2LoggingSystemProperties} instance.
+	 * @param environment the source environment
+	 * @param setter setter used to apply the property
+	 */
+	public Log4J2LoggingSystemProperties(Environment environment,
+			@Nullable BiConsumer<String, @Nullable String> setter) {
+		super(environment, setter);
+	}
+
+	/**
+	 * Create a new {@link Log4J2LoggingSystemProperties} instance.
+	 * @param environment the source environment
+	 * @param defaultValueResolver function used to resolve default values or {@code null}
+	 * @param setter setter used to apply the property or {@code null} for system
+	 * properties
+	 */
+	public Log4J2LoggingSystemProperties(Environment environment,
+			@Nullable Function<@Nullable String, @Nullable String> defaultValueResolver,
+			@Nullable BiConsumer<String, @Nullable String> setter) {
+		super(environment, defaultValueResolver, setter);
+	}
+
+	@Override
+	protected void apply(@Nullable LogFile logFile, PropertyResolver resolver) {
+		super.apply(logFile, resolver);
+		applyRollingPolicyProperties(resolver);
+	}
+
+	private void applyRollingPolicyProperties(PropertyResolver resolver) {
+		applyRollingPolicy(Log4J2RollingPolicySystemProperty.FILE_NAME_PATTERN, resolver);
+		applyRollingPolicy(Log4J2RollingPolicySystemProperty.MAX_FILE_SIZE, resolver, DataSize.class);
+		applyRollingPolicy(Log4J2RollingPolicySystemProperty.TOTAL_SIZE_CAP, resolver, DataSize.class);
+		applyRollingPolicy(Log4J2RollingPolicySystemProperty.MAX_HISTORY, resolver);
+	}
+
+	private void applyRollingPolicy(Log4J2RollingPolicySystemProperty property, PropertyResolver resolver) {
+		applyRollingPolicy(property, resolver, String.class);
+	}
+
+	private <T> void applyRollingPolicy(Log4J2RollingPolicySystemProperty property, PropertyResolver resolver,
+			Class<T> type) {
+		T value = getProperty(resolver, property.getApplicationPropertyName(), type);
+		if (value != null) {
+			String stringValue = String.valueOf((value instanceof DataSize dataSize) ? dataSize.toBytes() : value);
+			setSystemProperty(property.getEnvironmentVariableName(), stringValue);
+		}
+	}
+
+	@SuppressWarnings("unchecked")
+	private <T> @Nullable T getProperty(PropertyResolver resolver, String key, Class<T> type) {
+		try {
+			return resolver.getProperty(key, type);
+		}
+		catch (ConversionFailedException | ConverterNotFoundException ex) {
+			if (type != DataSize.class) {
+				throw ex;
+			}
+			String value = resolver.getProperty(key);
+			return (T) DataSize.parse(value);
+		}
+	}
+
+}

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2RollingPolicySystemProperty.java

@@ -0,0 +1,55 @@
+
+package org.springframework.boot.logging.log4j2;
+
+/**
+ * Log4j2 rolling policy system properties that can later be used by log configuration
+ * files.
+ *
+ * @see Log4J2LoggingSystemProperties
+ * @author Andrey Timonin
+ * @since 4.1.0
+ */
+public enum Log4J2RollingPolicySystemProperty {
+
+	/**
+	 * Logging system property for the rolled-over log file name pattern.
+	 */
+	FILE_NAME_PATTERN("file-name-pattern"),
+
+	/**
+	 * Logging system property for the file log max size.
+	 */
+	MAX_FILE_SIZE("max-file-size"),
+
+	/**
+	 * Logging system property for the file total size cap.
+	 */
+	TOTAL_SIZE_CAP("total-size-cap"),
+
+	/**
+	 * Logging system property for the file log max history.
+	 */
+	MAX_HISTORY("max-history");
+
+	private final String environmentVariableName;
+
+	private final String applicationPropertyName;
+
+	Log4J2RollingPolicySystemProperty(String applicationPropertyName) {
+		this.environmentVariableName = "LOG4J2_ROLLINGPOLICY_" + name();
+		this.applicationPropertyName = "logging.log4j2.rollingpolicy." + applicationPropertyName;
+	}
+
+	/**
+	 * Return the name of environment variable that can be used to access this property.
+	 * @return the environment variable name
+	 */
+	public String getEnvironmentVariableName() {
+		return this.environmentVariableName;
+	}
+
+	String getApplicationPropertyName() {
+		return this.applicationPropertyName;
+	}
+
+}

core/spring-boot/src/main/resources/org/springframework/boot/logging/log4j2/log4j2-file.xml

@@ -21,7 +21,7 @@
 				<ThresholdFilter level="${sys:CONSOLE_LOG_THRESHOLD:-TRACE}"/>
 			</Filters>
 		</Console>
-		<RollingFile name="File" fileName="${sys:LOG_FILE}" filePattern="${sys:LOG_PATH}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
+		<RollingFile name="File" fileName="${sys:LOG_FILE}" filePattern="${sys:LOG4J2_ROLLINGPOLICY_FILE_NAME_PATTERN:-${sys:LOG_PATH}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz}">
 			<Select>
 				<SystemPropertyArbiter propertyName="FILE_LOG_STRUCTURED_FORMAT">
 					<StructuredLogLayout format="${sys:FILE_LOG_STRUCTURED_FORMAT}" charset="${sys:FILE_LOG_CHARSET}"/>
@@ -34,8 +34,14 @@
 				<ThresholdFilter level="${sys:FILE_LOG_THRESHOLD:-TRACE}"/>
 			</Filters>
 			<Policies>
-				<SizeBasedTriggeringPolicy size="10 MB"/>
+				<SizeBasedTriggeringPolicy size="${sys:LOG4J2_ROLLINGPOLICY_MAX_FILE_SIZE:-10 MB}"/>
 			</Policies>
+			<DefaultRolloverStrategy max="${sys:LOG4J2_ROLLINGPOLICY_MAX_HISTORY:-7}">
+				<Delete basePath="${sys:LOG_PATH}" maxDepth="1">
+					<IfFileName glob="*.log.gz" />
+					<IfAccumulatedFileSize exceeds="${sys:LOG4J2_ROLLINGPOLICY_TOTAL_SIZE_CAP:-}"/>
+				</Delete>
+			</DefaultRolloverStrategy>
 		</RollingFile>
 	</Appenders>
 	<Loggers>

core/spring-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemPropertiesTests.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2012-present 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.HashSet;
+import java.util.Set;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.convert.ApplicationConversionService;
+import org.springframework.boot.logging.LoggingSystemProperty;
+import org.springframework.core.convert.support.ConfigurableConversionService;
+import org.springframework.mock.env.MockEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link Log4J2LoggingSystemProperties}.
+ *
+ * @author Andrey Timonin
+ */
+class Log4J2LoggingSystemPropertiesTests {
+
+	private Set<Object> systemPropertyNames;
+
+	private MockEnvironment environment;
+
+	@BeforeEach
+	void captureSystemPropertyNames() {
+		for (LoggingSystemProperty loggingSystemProperties : LoggingSystemProperty.values()) {
+			System.getProperties().remove(loggingSystemProperties);
+		}
+		this.systemPropertyNames = new HashSet<>(System.getProperties().keySet());
+		this.environment = new MockEnvironment();
+		this.environment
+			.setConversionService((ConfigurableConversionService) ApplicationConversionService.getSharedInstance());
+	}
+
+	@AfterEach
+	void restoreSystemProperties() {
+		System.getProperties().keySet().retainAll(this.systemPropertyNames);
+	}
+
+	@Test
+	void applySetsStandardSystemProperties() {
+		this.environment.setProperty("logging.threshold.console", "lts");
+		new Log4J2LoggingSystemProperties(this.environment).apply();
+		assertThat(System.getProperties())
+			.containsEntry(LoggingSystemProperty.CONSOLE_THRESHOLD.getEnvironmentVariableName(), "lts");
+	}
+
+	@Test
+	void applySetsLog4J2SystemProperties() {
+		this.environment.setProperty("logging.log4j2.rollingpolicy.file-name-pattern", "fnp");
+		this.environment.setProperty("logging.log4j2.rollingpolicy.max-file-size", "1KB");
+		this.environment.setProperty("logging.log4j2.rollingpolicy.total-size-cap", "2KB");
+		this.environment.setProperty("logging.log4j2.rollingpolicy.max-history", "mh");
+		new Log4J2LoggingSystemProperties(this.environment).apply();
+		assertThat(System.getProperties())
+			.containsEntry(Log4J2RollingPolicySystemProperty.FILE_NAME_PATTERN.getEnvironmentVariableName(), "fnp")
+			.containsEntry(Log4J2RollingPolicySystemProperty.MAX_FILE_SIZE.getEnvironmentVariableName(), "1024")
+			.containsEntry(Log4J2RollingPolicySystemProperty.TOTAL_SIZE_CAP.getEnvironmentVariableName(), "2048")
+			.containsEntry(Log4J2RollingPolicySystemProperty.MAX_HISTORY.getEnvironmentVariableName(), "mh");
+	}
+
+}