Automatic addition of the OTel Logback appender by the OTel starter

instrumentation/spring/spring-boot-autoconfigure/src/main/java/io/opentelemetry/instrumentation/spring/autoconfigure/instrumentation/logging/LogbackAppenderApplicationListener.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.spring.autoconfigure.instrumentation.logging;
+
+import ch.qos.logback.classic.LoggerContext;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.Appender;
+import io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender;
+import java.util.Iterator;
+import org.slf4j.ILoggerFactory;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
+import org.springframework.boot.context.logging.LoggingApplicationListener;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationEvent;
+import org.springframework.context.event.GenericApplicationListener;
+import org.springframework.core.ResolvableType;
+
+public class LogbackAppenderApplicationListener implements GenericApplicationListener {
+
+  private static final Class<?>[] SOURCE_TYPES = {
+    SpringApplication.class, ApplicationContext.class
+  };
+
+  private static final Class<?>[] EVENT_TYPES = {ApplicationEnvironmentPreparedEvent.class};
+
+  @Override
+  public boolean supportsSourceType(Class<?> sourceType) {
+    return isAssignableFrom(sourceType, SOURCE_TYPES);
+  }
+
+  @Override
+  public boolean supportsEventType(ResolvableType resolvableType) {
+    return isAssignableFrom(resolvableType.getRawClass(), EVENT_TYPES);
+  }
+
+  private static boolean isAssignableFrom(Class<?> type, Class<?>... supportedTypes) {
+    if (type != null) {
+      for (Class<?> supportedType : supportedTypes) {
+        if (supportedType.isAssignableFrom(type)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  @Override
+  public void onApplicationEvent(ApplicationEvent event) {
+    if (event instanceof ApplicationEnvironmentPreparedEvent // Event for which
+        // org.springframework.boot.context.logging.LoggingApplicationListener
+        // initializes logging
+        && !isOpenTelemetryAppenderAlreadyConfigured()) {
+      ch.qos.logback.classic.Logger logger =
+          (ch.qos.logback.classic.Logger)
+              LoggerFactory.getILoggerFactory().getLogger(Logger.ROOT_LOGGER_NAME);
+
+      OpenTelemetryAppender appender = new OpenTelemetryAppender();
+      appender.start();
+      logger.addAppender(appender);
+    }
+  }
+
+  private static boolean isOpenTelemetryAppenderAlreadyConfigured() {
+    ILoggerFactory loggerFactorySpi = LoggerFactory.getILoggerFactory();
+    if (!(loggerFactorySpi instanceof LoggerContext)) {
+      return false;
+    }
+    LoggerContext loggerContext = (LoggerContext) loggerFactorySpi;
+    for (ch.qos.logback.classic.Logger logger : loggerContext.getLoggerList()) {
+      Iterator<Appender<ILoggingEvent>> appenderIterator = logger.iteratorForAppenders();
+      while (appenderIterator.hasNext()) {
+        Appender<ILoggingEvent> appender = appenderIterator.next();
+        if (appender instanceof OpenTelemetryAppender) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  @Override
+  public int getOrder() {
+    return LoggingApplicationListener.DEFAULT_ORDER + 1; // To execute this listener just after
+    // org.springframework.boot.context.logging.LoggingApplicationListener
+  }
+}

instrumentation/spring/spring-boot-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -15,3 +15,6 @@ io.opentelemetry.instrumentation.spring.autoconfigure.instrumentation.webflux.Sp
 io.opentelemetry.instrumentation.spring.autoconfigure.instrumentation.webmvc.SpringWebMvc5InstrumentationAutoConfiguration,\
 io.opentelemetry.instrumentation.spring.autoconfigure.propagators.PropagationAutoConfiguration,\
 io.opentelemetry.instrumentation.spring.autoconfigure.resources.OtelResourceAutoConfiguration
+
+org.springframework.context.ApplicationListener=\
+io.opentelemetry.instrumentation.spring.autoconfigure.instrumentation.logging.LogbackAppenderApplicationListener

instrumentation/spring/spring-boot-autoconfigure/src/testLogbackAppender/java/io/opentelemetry/instrumentation/spring/autoconfigure/instrumentation/logging/LogbackAppenderTest.java

@@ -60,7 +60,9 @@ void shouldInitializeAppender() {
     LoggerFactory.getLogger("test").info("test log message");
 
     assertThat(testing.logRecords())
-        .anySatisfy(
+        .satisfiesOnlyOnce(
+            // OTel appender automatically added or from an XML file, it should not
+            // be added a second time by LogbackAppenderApplicationListener
             logRecord -> {
               assertThat(logRecord.getInstrumentationScopeInfo().getName()).isEqualTo("test");
               assertThat(logRecord.getBody().asString()).contains("test log message");