Allow auto-reload of log4j2 config

Log4j2 can auto-reload its configuration file as long as the reference
to a `java.io.File` is provided in the `ConfigurationSource`. Previously,
we always created such `ConfigurationSource` with only the URL regardless
of its type.

Detect when the configuration URL points to a File and create the
`ConfigurationSource` accordingly.

The `spring-boot-sample-actuator-log4j2` has been updated to reload the
logging configuration every 30 sec if necessary.

Fixes gh-3024, gh-3030

spring-boot-samples/spring-boot-sample-actuator-log4j2/src/main/resources/log4j2.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<Configuration status="WARN">
+<Configuration status="WARN" monitorInterval="30">
     <Properties>
         <Property name="PID">????</Property>
         <Property name="LOG_PATTERN">[%d{yyyy-MM-dd HH:mm:ss.SSS}] log4j2%X{context} - ${sys:PID} %5p [%t] --- %c{1}: %m%n</Property>

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

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.logging.log4j2;
 
+import java.io.IOException;
+import java.io.InputStream;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -48,6 +50,7 @@ import org.springframework.util.ResourceUtils;
  *
  * @author Daniel Fullarton
  * @author Andy Wilkinson
+ * @author Alexander Heusingfeld
  * @since 1.2.0
  */
 public class Log4J2LoggingSystem extends Slf4JLoggingSystem {
@@ -149,7 +152,7 @@ public class Log4J2LoggingSystem extends Slf4JLoggingSystem {
 		try {
 			LoggerContext ctx = getLoggerContext();
 			URL url = ResourceUtils.getURL(location);
-			ConfigurationSource source = new ConfigurationSource(url.openStream(), url);
+			ConfigurationSource source = getConfigurationSource(url);
 			ctx.start(ConfigurationFactory.getInstance().getConfiguration(source));
 		}
 		catch (Exception ex) {
@@ -158,6 +161,16 @@ public class Log4J2LoggingSystem extends Slf4JLoggingSystem {
 		}
 	}
 
+	private ConfigurationSource getConfigurationSource(URL url) throws IOException {
+		InputStream stream = url.openStream();
+		if (ResourceUtils.isFileURL(url)) {
+			return new ConfigurationSource(stream,
+						ResourceUtils.getFile(url));
+		} else {
+			return new ConfigurationSource(stream, url);
+		}
+	}
+
 	@Override
 	protected void reinitialize() {
 		getLoggerContext().reconfigure();

spring-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java

@@ -21,22 +21,27 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
+import com.fasterxml.jackson.databind.ObjectMapper;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.config.FileConfigurationMonitor;
 import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
+
 import org.springframework.boot.logging.AbstractLoggingSystemTests;
 import org.springframework.boot.logging.LogLevel;
 import org.springframework.boot.test.OutputCapture;
 import org.springframework.util.StringUtils;
 
-import com.fasterxml.jackson.databind.ObjectMapper;
-
 import static org.hamcrest.Matchers.arrayContaining;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.hamcrest.core.StringContains.containsString;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
@@ -72,6 +77,8 @@ public class Log4J2LoggingSystemTests extends AbstractLoggingSystemTests {
 		assertTrue("Wrong output:\n" + output, output.contains("Hello world"));
 		assertFalse("Output not hidden:\n" + output, output.contains("Hidden"));
 		assertFalse(new File(tmpDir() + "/spring.log").exists());
+		assertThat(this.loggingSystem.getConfiguration().getConfigurationSource()
+				.getFile(), is(notNullValue()));
 	}
 
 	@Test
@@ -84,6 +91,8 @@ public class Log4J2LoggingSystemTests extends AbstractLoggingSystemTests {
 		assertTrue("Wrong output:\n" + output, output.contains("Hello world"));
 		assertFalse("Output not hidden:\n" + output, output.contains("Hidden"));
 		assertTrue(new File(tmpDir() + "/spring.log").exists());
+		assertThat(this.loggingSystem.getConfiguration().getConfigurationSource()
+				.getFile(), is(notNullValue()));
 	}
 
 	@Test
@@ -96,6 +105,12 @@ public class Log4J2LoggingSystemTests extends AbstractLoggingSystemTests {
 		assertTrue("Wrong output:\n" + output, output.contains("Hello world"));
 		assertTrue("Wrong output:\n" + output, output.contains(tmpDir() + "/tmp.log"));
 		assertFalse(new File(tmpDir() + "/tmp.log").exists());
+		assertThat(this.loggingSystem.getConfiguration().getConfigurationSource()
+				.getFile().getAbsolutePath(), containsString("log4j2-nondefault.xml"));
+		// we assume that "log4j2-nondefault.xml" contains the 'monitorInterval'
+		// attribute, so we check that a monitor is created
+		assertThat(this.loggingSystem.getConfiguration().getConfigurationMonitor(),
+				is(instanceOf(FileConfigurationMonitor.class)));
 	}
 
 	@Test(expected = IllegalStateException.class)
@@ -167,6 +182,10 @@ public class Log4J2LoggingSystemTests extends AbstractLoggingSystemTests {
 			super(TestLog4J2LoggingSystem.class.getClassLoader());
 		}
 
+		public Configuration getConfiguration() {
+			return ((org.apache.logging.log4j.core.LoggerContext) LogManager.getContext(false)).getConfiguration();
+		}
+
 		@Override
 		protected boolean isClassAvailable(String className) {
 			return this.availableClasses.contains(className);

spring-boot/src/test/resources/log4j2-nondefault.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<Configuration status="WARN">
+<Configuration status="WARN" monitorInterval="30">
 	<Properties>
 		<Property name="PID">????</Property>
 		<Property name="LOG_PATTERN">${sys:LOG_FILE} %d{yyyy-MM-dd HH:mm:ss.SSS}] service%X{context} - ${sys:PID} %5p [%t] --- %c{1}: %m%n</Property>