improving documentation

pom.xml

@@ -7,12 +7,36 @@
 	<artifactId>raclette-java</artifactId>
 	<version>1.0-SNAPSHOT</version>
 
+    <properties>
+        <opentracing.version>0.22.0</opentracing.version>
+    </properties>
+
 	<dependencies>
+
+        <!-- Opentracing core -->
 		<dependency>
 			<groupId>io.opentracing</groupId>
 			<artifactId>opentracing-api</artifactId>
-			<version>0.21.0</version>
+			<version>${opentracing.version}</version>
 		</dependency>
+		<dependency>
+			<groupId>io.opentracing</groupId>
+			<artifactId>opentracing-noop</artifactId>
+			<version>${opentracing.version}</version>
+		</dependency>
+		<dependency>
+			<groupId>io.opentracing</groupId>
+			<artifactId>opentracing-util</artifactId>
+			<version>${opentracing.version}</version>
+		</dependency>
+
+        <!-- Tracer resolver -->
+        <dependency>
+            <groupId>io.opentracing.contrib</groupId>
+            <artifactId>opentracing-tracerresolver</artifactId>
+            <version>0.1.0</version>
+        </dependency>
+
 		<dependency>
 			<groupId>com.fasterxml.jackson.core</groupId>
 			<artifactId>jackson-databind</artifactId>
@@ -41,12 +65,7 @@
 			<version>4.9</version>
 		</dependency>
 
-		<!-- Tracer resolver -->
-		<dependency>
-			<groupId>io.opentracing.contrib</groupId>
-			<artifactId>opentracing-tracerresolver</artifactId>
-			<version>0.1.0</version>
-		</dependency>
+
 
 		<dependency>
 			<groupId>com.google.auto.service</groupId>
@@ -73,12 +92,7 @@
 			<version>2.7.22</version>
 			<scope>test</scope>
 		</dependency>
-        <dependency>
-            <groupId>io.opentracing.contrib</groupId>
-            <artifactId>opentracing-agent</artifactId>
-            <version>RELEASE</version>
-        </dependency>
-    </dependencies>
+	</dependencies>
 
 	<build>
 		<plugins>

src/main/java/com/datadoghq/trace/resolver/DDTracerResolver.java

@@ -34,10 +34,6 @@ public class DDTracerResolver extends TracerResolver {
 
     private final static Logger logger = LoggerFactory.getLogger(DDTracerResolver.class);
 
-//	private static final ServiceLoader<Writer> WRITERS = ServiceLoader.load(Writer.class);
-//	private static final ServiceLoader<Sampler> SAMPLERS = ServiceLoader.load(Sampler.class);
-//	private static final ServiceLoader<DDSpanContextDecorator> DECORATORS = ServiceLoader.load(DDSpanContextDecorator.class);
-
     public static final String TRACER_CONFIG = "dd-trace.yaml";
     private final ObjectMapper objectMapper = new ObjectMapper(new YAMLFactory());
 
@@ -129,10 +125,10 @@ public class DDTracerResolver extends TracerResolver {
         }
 
         if (tracer == null) {
-            tracer =  NoopTracerFactory.create();
+            tracer = NoopTracerFactory.create();
         }
 
         GlobalTracer.register(tracer);
-        return  tracer;
+        return tracer;
     }
 }

src/main/resources/dd-trace.yaml

@@ -1,13 +1,36 @@
+# Service name used if none is provided in the app
 defaultServiceName: unnamed-java-app
+
+# The writer to use.
+# Could be: LoggingWritter or DDAgentWriter (default)
 writer:
+  # LoggingWriter: Spans are logged using the application configuration
+  # DDAgentWriter: Spans are forwarding to a Datadog Agent
+  #  - Param 'host': the hostname where the DD Agent running (default: localhost)
+  #  - Param 'port': the port to reach the DD Agent (default: 8126)
   type: DDAgentWriter
   host: localhost
   port: 8126
+
+# The sampler to use.
+# Could be: AllSampler (default) or RateSampler
 sampler:
+  # AllSampler: all spans are reported to the writer
+  # RateSample: only a portion of spans are reported to the writer
+  #  - Param 'rate': the portion of spans to keep
   type: AllSampler
-#decorators:
-#  - type: HTTPServiceDecorator
-#    componentName: hello
-#    desiredServiceName: world
-    
+
+# Decorators are used to add extra information to span
+# Could be DBServiceDecorator, MapperDecorator or HTTPServiceDecorator
+decorators:
+
+  # This span decorator leverages HTTP tags such as the URL requested
+  - type: HTTPServiceDecorator
+    componentName: http
+    desiredServiceName: unnamed-java-http
+
+  # This span decorator leverages DB tags such as the statement requested
+   - type: DBServiceDecorator
+    componentName: db
+    desiredServiceName: unnamed-java-db