Add Minimal OpenTelemetry Java Reference Application for Getting Started Guide

README.md

@@ -6,6 +6,10 @@ of them assume you have docker running on your local machine.
 
 ## Example modules:
 
+- [OpenTelemetry Reference Application](reference-application)
+    - A comprehensive reference application demonstrating OpenTelemetry usage following the 
+      [Getting Started Reference Application Specification](https://opentelemetry.io/docs/getting-started/reference-application-specification/).
+    - Includes traces, metrics, logs, manual instrumentation, Docker setup with collector, and multiple configuration approaches.
 - [Using the SDK AutoConfiguration module](autoconfigure)
     - This module contains a fully-functional example of using the autoconfigure
       SDK extension module to configure the SDK using only environment

reference-application/Dockerfile

@@ -0,0 +1,13 @@
+FROM openjdk:17-jdk-slim
+
+WORKDIR /app
+
+# Copy the JAR file and agent
+COPY build/libs/app.jar /app.jar
+COPY build/agent/opentelemetry-javaagent.jar /opentelemetry-javaagent.jar
+
+# Expose the port
+EXPOSE 8080
+
+# Run the application with the Java agent
+ENTRYPOINT ["java", "-javaagent:/opentelemetry-javaagent.jar", "-jar", "/app.jar"]

reference-application/README.md

@@ -0,0 +1,183 @@
+# OpenTelemetry Java Reference Application
+
+This reference application demonstrates comprehensive OpenTelemetry usage in Java, following the [OpenTelemetry Getting Started Reference Application Specification](https://opentelemetry.io/docs/getting-started/reference-application-specification/).
+
+## Features
+
+This application showcases:
+
+- **Traces**: Manual and automatic span creation, distributed tracing
+- **Metrics**: Custom metrics, performance monitoring
+- **Logs**: Structured logging with trace correlation
+- **Multiple exporters**: Console, OTLP, file-based exports
+- **Configuration**: Environment variables, programmatic setup, and declarative configuration
+- **Docker support**: Complete setup with OpenTelemetry Collector
+
+## Application Overview
+
+The reference application is a dice rolling service that demonstrates OpenTelemetry capabilities using the **OpenTelemetry Java Agent** for automatic instrumentation and manual instrumentation examples:
+
+### Endpoints
+
+- `GET /rolldice` - Basic dice roll (returns random 1-6)
+- `GET /rolldice?player=<name>` - Dice roll for a specific player
+- `GET /rolldice?rolls=<n>` - Roll multiple dice
+- `GET /fibonacci?n=<number>` - Calculate fibonacci (demonstrates computation tracing)
+- `GET /health` - Health check endpoint
+- `GET /metrics` - Prometheus metrics endpoint (when enabled)
+
+### Scenarios Demonstrated
+
+1. **Basic HTTP instrumentation**: Automatic span creation for HTTP requests
+2. **Manual instrumentation**: Custom spans for business logic
+3. **Error handling**: Error span recording and exception tracking
+4. **Custom metrics**: Performance counters, histograms, gauges
+5. **Baggage propagation**: Cross-cutting concerns
+6. **Resource detection**: Automatic resource attribute detection
+
+## Quick Start
+
+### Prerequisites
+
+- Java 17 or later
+- Docker and Docker Compose (for collector setup)
+
+### Running with Console Output
+
+```shell
+# Build the application with the Java agent
+../gradlew bootJar
+
+# Run with the Java agent for automatic instrumentation
+java -javaagent:build/agent/opentelemetry-javaagent.jar -jar build/libs/app.jar
+```
+
+Then test the endpoints:
+```shell
+curl http://localhost:8080/rolldice
+curl http://localhost:8080/rolldice?player=alice
+curl http://localhost:8080/fibonacci?n=10
+```
+
+### Running with OpenTelemetry Collector
+
+```shell
+# Build the application
+../gradlew bootJar
+
+# Start the collector and application
+docker-compose up --build
+```
+
+This will:
+- Start the reference application on port 8080
+- Start OpenTelemetry Collector on port 4317/4318
+- Export telemetry data to the collector
+- Output structured telemetry data to console
+
+## Configuration
+
+The application supports multiple configuration approaches:
+
+### Environment Variables
+
+```shell
+export OTEL_SERVICE_NAME=dice-server
+export OTEL_SERVICE_VERSION=1.0.0
+export OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318
+export OTEL_TRACES_EXPORTER=otlp
+export OTEL_METRICS_EXPORTER=otlp
+export OTEL_LOGS_EXPORTER=otlp
+```
+
+### Java Agent Configuration
+
+The application uses the OpenTelemetry Java Agent which automatically configures instrumentation based on environment variables and system properties. All standard OpenTelemetry configuration options are supported.
+
+### Declarative Configuration
+
+Use the included `otel-config.yaml` for file-based configuration:
+
+```shell
+export OTEL_EXPERIMENTAL_CONFIG_FILE=otel-config.yaml
+```
+
+## Understanding the Output
+
+### Traces
+
+The application creates spans for:
+- HTTP requests (automatic)
+- Business logic operations (manual)
+- External calls and computations
+- Error scenarios
+
+### Metrics
+
+The application reports:
+- Request duration histograms
+- Request counters by endpoint
+- Error rates
+- Custom business metrics (dice roll distributions)
+
+### Logs
+
+All logs include:
+- Trace ID and Span ID for correlation
+- Structured fields
+- Different log levels
+- Business context
+
+## Development
+
+### Building
+
+```shell
+../gradlew build
+```
+
+### Testing
+
+```shell
+../gradlew test
+```
+
+### Running locally
+
+```shell
+../gradlew bootRun
+```
+
+## Docker Images
+
+The application can be built as a Docker image:
+
+```shell
+../gradlew bootBuildImage
+```
+
+## Troubleshooting
+
+### Common Issues
+
+1. **No telemetry data**: Check OTEL_* environment variables
+2. **Connection issues**: Verify collector endpoint configuration
+3. **Missing traces**: Ensure sampling is configured correctly
+
+### Debugging
+
+Enable debug logging:
+```shell
+export OTEL_JAVAAGENT_DEBUG=true
+```
+
+Or set logging level:
+```shell
+export LOGGING_LEVEL_IO_OPENTELEMETRY=DEBUG
+```
+
+## Learn More
+
+- [OpenTelemetry Java Documentation](https://opentelemetry.io/docs/languages/java/)
+- [OpenTelemetry Specification](https://opentelemetry.io/docs/specs/otel/)
+- [Semantic Conventions](https://opentelemetry.io/docs/specs/semconv/)

reference-application/build.gradle.kts

@@ -0,0 +1,58 @@
+import org.springframework.boot.gradle.plugin.SpringBootPlugin
+import org.springframework.boot.gradle.tasks.bundling.BootJar
+
+plugins {
+    id("java")
+    id("org.springframework.boot") version "3.5.6"
+}
+
+val moduleName by extra { "io.opentelemetry.examples.reference-application" }
+
+repositories {
+    mavenCentral()
+}
+
+val agent = configurations.create("agent")
+
+dependencies {
+    implementation(platform(SpringBootPlugin.BOM_COORDINATES))
+    implementation("io.opentelemetry:opentelemetry-api")
+
+    // Spring Boot
+    implementation("org.springframework.boot:spring-boot-starter-web")
+    implementation("org.springframework.boot:spring-boot-starter-actuator")
+
+    // OpenTelemetry Instrumentation - use logback appender for logs
+    implementation("io.opentelemetry.instrumentation:opentelemetry-logback-appender-1.0")
+
+    // Micrometer for additional metrics
+    implementation("io.micrometer:micrometer-registry-prometheus")
+
+    // Java agent
+    agent("io.opentelemetry.javaagent:opentelemetry-javaagent:2.20.1")
+
+    // Testing
+    testImplementation("org.springframework.boot:spring-boot-starter-test")
+    testImplementation("io.opentelemetry:opentelemetry-sdk-testing")
+}
+
+val copyAgent = tasks.register<Copy>("copyAgent") {
+    from(agent.singleFile)
+    into(layout.buildDirectory.dir("agent"))
+    rename("opentelemetry-javaagent-.*\\.jar", "opentelemetry-javaagent.jar")
+}
+
+tasks.named<BootJar>("bootJar") {
+    dependsOn(copyAgent)
+    archiveFileName = "app.jar"
+}
+
+tasks.withType<Test> {
+    useJUnitPlatform()
+}
+
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(17))
+    }
+}

reference-application/docker-compose.yml

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+services:
+  dice-server:
+    build: .
+    ports:
+      - "8080:8080"
+    environment:
+      - OTEL_SERVICE_NAME=dice-server
+      - OTEL_SERVICE_VERSION=1.0.0
+      - OTEL_EXPORTER_OTLP_ENDPOINT=http://otel-collector:4318
+      - OTEL_TRACES_EXPORTER=otlp
+      - OTEL_METRICS_EXPORTER=otlp
+      - OTEL_LOGS_EXPORTER=otlp
+      - OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf
+    depends_on:
+      - otel-collector
+
+  otel-collector:
+    image: otel/opentelemetry-collector-contrib:latest
+    ports:
+      - "4317:4317"   # OTLP gRPC
+      - "4318:4318"   # OTLP HTTP
+      - "8889:8889"   # Prometheus metrics
+    volumes:
+      - ./otel-collector-config.yaml:/etc/otelcol-contrib/otel-collector-config.yaml
+    command: ["--config=/etc/otelcol-contrib/otel-collector-config.yaml"]
+
+  prometheus:
+    image: prom/prometheus:latest
+    ports:
+      - "9090:9090"
+    volumes:
+      - ./prometheus.yml:/etc/prometheus/prometheus.yml
+    command:
+      - '--config.file=/etc/prometheus/prometheus.yml'
+      - '--storage.tsdb.path=/prometheus'
+      - '--web.console.libraries=/etc/prometheus/console_libraries'
+      - '--web.console.templates=/etc/prometheus/consoles'

reference-application/otel-collector-config.yaml

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+receivers:
+  otlp:
+    protocols:
+      grpc:
+        endpoint: 0.0.0.0:4317
+      http:
+        endpoint: 0.0.0.0:4318
+
+processors:
+  batch:
+  memory_limiter:
+    limit_mib: 512
+
+exporters:
+  logging:
+    loglevel: info
+    sampling_initial: 5
+    sampling_thereafter: 200
+
+  prometheus:
+    endpoint: "0.0.0.0:8889"
+    metric_expiration: 180m
+    enable_open_metrics: true
+
+extensions:
+  health_check:
+    endpoint: 0.0.0.0:13133
+  pprof:
+    endpoint: 0.0.0.0:1777
+  zpages:
+    endpoint: 0.0.0.0:55679
+
+service:
+  extensions: [health_check, pprof, zpages]
+  pipelines:
+    traces:
+      receivers: [otlp]
+      processors: [memory_limiter, batch]
+      exporters: [logging]
+    metrics:
+      receivers: [otlp]
+      processors: [memory_limiter, batch]
+      exporters: [logging, prometheus]
+    logs:
+      receivers: [otlp]
+      processors: [memory_limiter, batch]
+      exporters: [logging]

reference-application/otel-config.yaml

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+file_format: 0.3
+
+# Service configuration
+resource:
+  attributes:
+    service.name: dice-server
+    service.version: 1.0.0
+    deployment.environment: local
+
+# Tracer provider configuration
+tracer_provider:
+  processors:
+    - batch:
+        exporter:
+          console: {}
+  sampler:
+    parent_based:
+      root:
+        always_on: {}
+
+# Meter provider configuration  
+meter_provider:
+  readers:
+    - periodic:
+        exporter:
+          console: {}
+        interval: 30000
+
+# Logger provider configuration
+logger_provider:
+  processors:
+    - batch:
+        exporter:
+          console: {}
+
+# Propagators
+propagators:
+  - tracecontext
+  - baggage