Sketch out slf4j bridge

build.gradle.kts

@@ -13,12 +13,13 @@ subprojects {
     version = "0.1.0-SNAPSHOT"
 
     repositories {
+        mavenLocal()
         mavenCentral()
     }
 
     dependencies {
         // using the bom ensures that all of your opentelemetry dependency versions are aligned
-        implementation(platform("io.opentelemetry.instrumentation:opentelemetry-instrumentation-bom-alpha:2.22.0-alpha"))
+        implementation(platform("io.opentelemetry.instrumentation:opentelemetry-instrumentation-bom-alpha:2.23.0-alpha-SNAPSHOT"))
     }
 
     spotless {

log-appender-log4j2/README.md

@@ -0,0 +1,34 @@
+# OpenTelemetry with Log4j2
+
+This sample app demonstrates an application emitting logs through a variety of logging APIs (OpenTelemetry API, log4j1, log4j2, JUL, slf4j) and configuring those logs to be sent an OTLP receiver via the OpenTelemetry SDK, and to the console via log4j2.
+
+* Install and run a OTLP receiver listening at `localhost:4318`. [otel-tui](https://github.com/ymtdzzz/otel-tui) is a good choice for local development.
+
+* Run the application:
+
+```shell
+../gradlew run
+
+> Task :opentelemetry-examples-log-appender-log4j2:run
+log4j2: 08:49:54.249 [main] INFO  log4j2-logger - A log4j2 log message.
+log4j2: 08:49:54.263 [main] INFO  log4j1-logger - A log4j1 log message.
+log4j2: 08:49:54.263 [main] INFO  slf4j-logger - A slf4j log message.
+log4j2: 08:49:54.263 [main] INFO  jul-logger - A JUL log message.
+log4j2: 08:49:54.265 [main] INFO  otel-logger - An OTEL log message.
+```
+
+* Or run the application with the javaagent:
+
+```shell
+../gradlew run -PrunWithAgent
+
+> Task :opentelemetry-examples-log-appender-log4j2:run
+[otel.javaagent 2025-12-08 08:54:48:330 -0600] [main] INFO io.opentelemetry.javaagent.tooling.VersionLogger - opentelemetry-javaagent - version: 2.23.0-SNAPSHOT
+log4j2: 08:54:55.599 [main] INFO  log4j2-logger - A log4j2 log message.
+log4j2: 08:54:55.625 [main] INFO  log4j1-logger - A log4j1 log message.
+log4j2: 08:54:55.626 [main] INFO  slf4j-logger - A slf4j log message.
+log4j2: 08:54:55.626 [main] INFO  jul-logger - A JUL log message.
+log4j2: 08:54:55.629 [main] INFO  otel-logger - An OTEL log message.
+```
+
+* A log message from each logging API appears exactly once in the console and OTLP receiver

log-appender-log4j2/build.gradle.kts

@@ -0,0 +1,81 @@
+plugins {
+    id("java")
+    id("application")
+}
+
+description = "OpenTelemetry Log4j2 SDK Example"
+val moduleName by extra { "io.opentelemetry.examples.log-appender" }
+
+java {
+    toolchain {
+        // logback 1.4.x+ requires java 11
+        languageVersion.set(JavaLanguageVersion.of(11))
+    }
+}
+
+val agent = configurations.create("agent")
+
+dependencies {
+    implementation(platform("org.apache.logging.log4j:log4j-bom:2.25.2"))
+
+    // Slf4J API
+    implementation("org.slf4j:slf4j-api:2.0.17")
+    // Log4j2 API
+    implementation("org.apache.logging.log4j:log4j-api")
+    // Log4j1 API (and bridge to SLF4J)
+    implementation("org.slf4j:log4j-over-slf4j:2.0.17")
+    // OTEL API
+    implementation("io.opentelemetry:opentelemetry-api")
+
+    // JUL to SLF4J bridge
+    implementation("org.slf4j:jul-to-slf4j:2.0.17")
+    // Log4j1 to SLF4J bridge
+    implementation("org.slf4j:slf4j-api:2.0.17")
+
+    // SLF4J binding for Log4j2
+    implementation("org.apache.logging.log4j:log4j-slf4j2-impl")
+
+    // Log4j2 SDK
+    implementation("org.apache.logging.log4j:log4j-core")
+    implementation("io.opentelemetry.instrumentation:opentelemetry-log4j-appender-2.17")
+
+    // OTEL SDK
+    implementation("io.opentelemetry:opentelemetry-sdk")
+    implementation("io.opentelemetry:opentelemetry-exporter-otlp")
+    implementation("io.opentelemetry:opentelemetry-sdk-extension-incubator")
+
+    agent("io.opentelemetry.javaagent:opentelemetry-javaagent:2.23.0-SNAPSHOT")
+}
+
+val copyAgent = tasks.register<Copy>("copyAgent") {
+    from(agent.singleFile)
+    into(layout.buildDirectory.dir("agent"))
+    rename("opentelemetry-javaagent-.*\\.jar", "opentelemetry-javaagent.jar")
+}
+
+tasks.getByName("run") {
+    dependsOn(copyAgent)
+}
+
+application {
+    mainClass = "io.opentelemetry.example.logappender.Application"
+
+    if (project.hasProperty("runWithAgent")) {
+        applicationDefaultJvmArgs = listOf("-javaagent:build/agent/opentelemetry-javaagent.jar")
+    }
+}
+
+tasks.register<JavaExec>("runWithoutAgent") {
+    group = ApplicationPlugin.APPLICATION_GROUP
+    classpath = sourceSets.main.get().runtimeClasspath
+    mainClass = "io.opentelemetry.example.logappender.Application"
+}
+
+tasks.register<JavaExec>("runWithAgent") {
+    dependsOn(copyAgent)
+
+    group = ApplicationPlugin.APPLICATION_GROUP
+    classpath = sourceSets.main.get().runtimeClasspath
+    mainClass = "io.opentelemetry.example.logappender.Application"
+    jvmArgs = listOf("-javaagent:build/agent/opentelemetry-javaagent.jar")
+}

log-appender-log4j2/src/main/java/io/opentelemetry/example/logappender/Application.java

@@ -0,0 +1,84 @@
+package io.opentelemetry.example.logappender;
+
+import static io.opentelemetry.semconv.ServiceAttributes.SERVICE_NAME;
+
+import io.opentelemetry.api.GlobalOpenTelemetry;
+import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.logs.Severity;
+import io.opentelemetry.exporter.otlp.http.logs.OtlpHttpLogRecordExporter;
+import io.opentelemetry.instrumentation.log4j.appender.v2_17.OpenTelemetryAppender;
+import io.opentelemetry.sdk.OpenTelemetrySdk;
+import io.opentelemetry.sdk.extension.incubator.slf4j.Slf4jBridgeProcessor;
+import io.opentelemetry.sdk.logs.SdkLoggerProvider;
+import io.opentelemetry.sdk.logs.export.BatchLogRecordProcessor;
+import io.opentelemetry.sdk.resources.Resource;
+import io.opentelemetry.sdk.trace.SdkTracerProvider;
+import io.opentelemetry.sdk.trace.samplers.Sampler;
+import java.util.logging.Logger;
+import org.apache.logging.log4j.LogManager;
+import org.slf4j.LoggerFactory;
+import org.slf4j.bridge.SLF4JBridgeHandler;
+
+public class Application {
+
+  public static void main(String[] args) {
+    // If javaagent isn't installed, initialize opentelemetry SDK and install it in the log4j2
+    // OpenTelemetryAppender
+    OpenTelemetry openTelemetry;
+    if (!GlobalOpenTelemetry.isSet()) {
+      openTelemetry = initializeOpenTelemetry();
+      OpenTelemetryAppender.install(openTelemetry);
+    } else {
+      openTelemetry = GlobalOpenTelemetry.get();
+    }
+
+    // Install JUL to SLF4J bridging
+    SLF4JBridgeHandler.removeHandlersForRootLogger();
+    SLF4JBridgeHandler.install();
+
+    // Initialize loggers and log from all APIs
+
+    // log4j2
+    org.apache.logging.log4j.Logger log4j2Logger = LogManager.getLogger("log4j2-logger");
+    log4j2Logger.info("A log4j2 log message.");
+
+    // log4j1
+    org.apache.log4j.Logger log4j1Logger = org.apache.log4j.Logger.getLogger("log4j1-logger");
+    log4j1Logger.info("A log4j1 log message.");
+
+    // slf4j
+    org.slf4j.Logger slf4jLogger = LoggerFactory.getLogger("slf4j-logger");
+    slf4jLogger.info("A slf4j log message.");
+
+    // jul
+    java.util.logging.Logger julLogger = Logger.getLogger("jul-logger");
+    julLogger.info("A JUL log message.");
+
+    // otel
+    io.opentelemetry.api.logs.Logger otelLogger = openTelemetry.getLogsBridge().get("otel-logger");
+    otelLogger.logRecordBuilder().setSeverity(Severity.INFO).setBody("An OTEL log message.").emit();
+  }
+
+  private static OpenTelemetry initializeOpenTelemetry() {
+    OpenTelemetrySdk sdk =
+        OpenTelemetrySdk.builder()
+            .setTracerProvider(SdkTracerProvider.builder().setSampler(Sampler.alwaysOn()).build())
+            .setLoggerProvider(
+                SdkLoggerProvider.builder()
+                    .setResource(
+                        Resource.getDefault().toBuilder()
+                            .put(SERVICE_NAME, "log4j-example")
+                            .build())
+                    .addLogRecordProcessor(Slf4jBridgeProcessor.create())
+                    .addLogRecordProcessor(
+                        BatchLogRecordProcessor.builder(OtlpHttpLogRecordExporter.builder().build())
+                            .build())
+                    .build())
+            .build();
+
+    // Add hook to close SDK, which flushes logs
+    Runtime.getRuntime().addShutdownHook(new Thread(sdk::close));
+
+    return sdk;
+  }
+}

log-appender-log4j2/src/main/resources/log4j2.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Configuration status="WARN">
+    <Appenders>
+        <Console name="ConsoleAppender" target="SYSTEM_OUT" follow="true">
+            <PatternLayout pattern="log4j2: %d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
+        </Console>
+        <OpenTelemetry name="OpenTelemetryAppender" captureMapMessageAttributes="true" captureExperimentalAttributes="true"/>
+    </Appenders>
+    <Loggers>
+        <Root level="info">
+            <AppenderRef ref="OpenTelemetryAppender" />
+            <AppenderRef ref="ConsoleAppender" />
+        </Root>
+    </Loggers>
+</Configuration>

log-appender-logback/README.md

@@ -0,0 +1,34 @@
+# OpenTelemetry with Logback
+
+This sample app demonstrates an application emitting logs through a variety of logging APIs (OpenTelemetry API, log4j1, log4j2, JUL, slf4j) and configuring those logs to be sent an OTLP receiver via the OpenTelemetry SDK, and to the console via logback.
+
+* Install and run a OTLP receiver listening at `localhost:4318`. [otel-tui](https://github.com/ymtdzzz/otel-tui) is a good choice for local development.
+
+* Run the application:
+
+```shell
+../gradlew run
+
+> Task :opentelemetry-examples-log-appender-logback:run
+logback: 08:53:12.625 [main] INFO  log4j2-logger - A log4j2 log message.
+logback: 08:53:12.633 [main] INFO  log4j1-logger - A log4j1 log message.
+logback: 08:53:12.633 [main] INFO  slf4j-logger - A slf4j log message.
+logback: 08:53:12.633 [main] INFO  jul-logger - A JUL log message.
+logback: 08:53:12.634 [main] INFO  otel-logger - An OTEL log message.
+```
+
+* Or run the application with the javaagent:
+
+```shell
+../gradlew run -PrunWithAgent
+
+> Task :opentelemetry-examples-log-appender-logback:run
+logback: 08:47:33.317 [main] INFO  i.o.javaagent.tooling.VersionLogger - opentelemetry-javaagent - version: 2.23.0-SNAPSHOT
+logback: 08:47:33.337 [main] INFO  log4j2-logger - A log4j2 log message.
+logback: 08:47:33.340 [main] INFO  log4j1-logger - A log4j1 log message.
+logback: 08:47:33.340 [main] INFO  slf4j-logger - A slf4j log message.
+logback: 08:47:33.340 [main] INFO  jul-logger - A JUL log message.
+logback: 08:47:33.343 [main] INFO  otel-logger - An OTEL log message.
+```
+
+* A log message from each logging API appears exactly once in the console and OTLP receiver

log-appender-logback/build.gradle.kts

@@ -0,0 +1,78 @@
+plugins {
+    id("java")
+    id("application")
+}
+
+description = "OpenTelemetry Logback SDK Example"
+val moduleName by extra { "io.opentelemetry.examples.log-appender" }
+
+java {
+    toolchain {
+        // logback 1.4.x+ requires java 11
+        languageVersion.set(JavaLanguageVersion.of(11))
+    }
+}
+
+val agent = configurations.create("agent")
+
+dependencies {
+    implementation(platform("org.apache.logging.log4j:log4j-bom:2.25.2"))
+
+    // Slf4J API
+    implementation("org.slf4j:slf4j-api:2.0.17")
+    // Log4j2 API
+    implementation("org.apache.logging.log4j:log4j-api")
+    // Log4j1 API (and bridge to SLF4J)
+    implementation("org.slf4j:log4j-over-slf4j:2.0.17")
+    // OTEL API
+    implementation("io.opentelemetry:opentelemetry-api")
+
+    // JUL to SLF4J bridge
+    implementation("org.slf4j:jul-to-slf4j:2.0.17")
+    // Log4j2 to SLF4J bridge
+    implementation("org.apache.logging.log4j:log4j-to-slf4j")
+
+    // Logback SDK and SLF4J binding for logback
+    implementation("ch.qos.logback:logback-classic:1.5.21")
+    implementation("io.opentelemetry.instrumentation:opentelemetry-logback-appender-1.0")
+
+    // OTEL SDK
+    implementation("io.opentelemetry:opentelemetry-sdk")
+    implementation("io.opentelemetry:opentelemetry-exporter-otlp")
+    implementation("io.opentelemetry:opentelemetry-sdk-extension-incubator")
+
+    agent("io.opentelemetry.javaagent:opentelemetry-javaagent:2.23.0-SNAPSHOT")
+}
+
+val copyAgent = tasks.register<Copy>("copyAgent") {
+    from(agent.singleFile)
+    into(layout.buildDirectory.dir("agent"))
+    rename("opentelemetry-javaagent-.*\\.jar", "opentelemetry-javaagent.jar")
+}
+
+tasks.getByName("run") {
+    dependsOn(copyAgent)
+}
+
+application {
+    mainClass = "io.opentelemetry.example.logappender.Application"
+
+    if (project.hasProperty("runWithAgent")) {
+        applicationDefaultJvmArgs = listOf("-javaagent:build/agent/opentelemetry-javaagent.jar")
+    }
+}
+
+tasks.register<JavaExec>("runWithoutAgent") {
+    group = ApplicationPlugin.APPLICATION_GROUP
+    classpath = sourceSets.main.get().runtimeClasspath
+    mainClass = "io.opentelemetry.example.logappender.Application"
+}
+
+tasks.register<JavaExec>("runWithAgent") {
+    dependsOn(copyAgent)
+
+    group = ApplicationPlugin.APPLICATION_GROUP
+    classpath = sourceSets.main.get().runtimeClasspath
+    mainClass = "io.opentelemetry.example.logappender.Application"
+    jvmArgs = listOf("-javaagent:build/agent/opentelemetry-javaagent.jar")
+}