Support profile specific Log4j2 configuration

Add a `SpringProfileArbiter` Log4j2 plugin which allows Log4j2
configuration to be included or skipped based on the active Spring
`Environment` profiles.

See gh-32734

Author: rgoers

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

@@ -0,0 +1,138 @@
+/*
+ * Copyright 2012-2022 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 org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.core.LoggerContext;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.config.Node;
+import org.apache.logging.log4j.core.config.arbiters.Arbiter;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
+import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
+import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
+import org.apache.logging.log4j.core.config.plugins.PluginLoggerContext;
+import org.apache.logging.log4j.status.StatusLogger;
+
+import org.springframework.core.env.Environment;
+import org.springframework.core.env.Profiles;
+import org.springframework.util.StringUtils;
+
+/**
+ * An Arbiter that uses the active Spring profile to determine if configuration should be
+ * included.
+ *
+ * @author Ralph Goers
+ * @since 3.0.0
+ */
+@Plugin(name = "SpringProfile", category = Node.CATEGORY, elementType = Arbiter.ELEMENT_TYPE, deferChildren = true,
+		printObject = true)
+public final class SpringProfileArbiter implements Arbiter {
+
+	private final String[] profileNames;
+
+	private final Environment environment;
+
+	private SpringProfileArbiter(final String[] profiles, Environment environment) {
+		this.profileNames = profiles;
+		this.environment = environment;
+	}
+
+	@Override
+	public boolean isCondition() {
+		if (this.environment == null) {
+			return false;
+		}
+
+		if (this.profileNames.length == 0) {
+			return false;
+		}
+		return this.environment.acceptsProfiles(Profiles.of(this.profileNames));
+	}
+
+	@PluginBuilderFactory
+	public static Builder newBuilder() {
+		return new Builder();
+	}
+
+	/**
+	 * Standard Builder to create the Arbiter.
+	 */
+	public static class Builder implements org.apache.logging.log4j.core.util.Builder<SpringProfileArbiter> {
+
+		private static final Logger LOGGER = StatusLogger.getLogger();
+
+		/**
+		 * Attribute name identifier.
+		 */
+		public static final String ATTR_NAME = "name";
+
+		@PluginBuilderAttribute(ATTR_NAME)
+		private String name;
+
+		@PluginConfiguration
+		private Configuration configuration;
+
+		@PluginLoggerContext
+		private LoggerContext loggerContext;
+
+		/**
+		 * Sets the Profile Name or Names.
+		 * @param name the profile name(s).
+		 * @return this
+		 */
+		public Builder setName(final String name) {
+			this.name = name;
+			return asBuilder();
+		}
+
+		public Builder setConfiguration(final Configuration configuration) {
+			this.configuration = configuration;
+			return asBuilder();
+		}
+
+		public Builder setLoggerContext(final LoggerContext loggerContext) {
+			this.loggerContext = loggerContext;
+			return asBuilder();
+		}
+
+		private SpringProfileArbiter.Builder asBuilder() {
+			return this;
+		}
+
+		public SpringProfileArbiter build() {
+			String[] profileNames = StringUtils.trimArrayElements(StringUtils
+					.commaDelimitedListToStringArray(this.configuration.getStrSubstitutor().replace(this.name)));
+			Environment environment = null;
+			if (this.loggerContext != null) {
+				environment = (Environment) this.loggerContext.getObject(Log4J2LoggingSystem.ENVIRONMENT_KEY);
+				if (environment == null) {
+					LOGGER.warn("Cannot create Arbiter, no Spring Environment provided");
+					return null;
+				}
+
+				return new SpringProfileArbiter(profileNames, environment);
+			}
+			else {
+				LOGGER.warn("Cannot create Arbiter, LoggerContext is not available");
+			}
+			return null;
+		}
+
+	}
+
+}