Addresses #1043: add a serviceName attribute to the @Trace annotation

dd-java-agent/instrumentation/trace-annotation/src/main/java/datadog/trace/instrumentation/trace_annotation/TraceAdvice.java

@@ -28,6 +28,12 @@ public static AgentScope onEnter(@Advice.Origin final Method method) {
       resourceName = DECORATE.spanNameForMethod(method);
     }
     span.setResourceName(resourceName);
+
+    String serviceName = traceAnnotation == null ? null : traceAnnotation.serviceName();
+    if (serviceName != null && serviceName.length() > 0) {
+      span.setServiceName(serviceName);
+    }
+
     DECORATE.afterStart(span);
 
     final AgentScope scope = activateSpan(span);

dd-java-agent/instrumentation/trace-annotation/src/test/groovy/TraceAnnotationsTest.groovy

@@ -77,6 +77,29 @@ class TraceAnnotationsTest extends AgentTestRunner {
     }
   }
 
+  def "test simple case with only service name set"() {
+    setup:
+    // Test single span in new trace
+    SayTracedHello.sayHelloWithServiceName()
+
+    expect:
+    assertTraces(1) {
+      trace(1) {
+        span {
+          serviceName "testServiceName"
+          resourceName "SayTracedHello.sayHelloWithServiceName"
+          operationName "trace.annotation"
+          parent()
+          errored false
+          tags {
+            "$Tags.COMPONENT" "trace"
+            defaultTags()
+          }
+        }
+      }
+    }
+  }
+
   def "test simple case with both resource and operation name set"() {
     setup:
     // Test single span in new trace

dd-java-agent/instrumentation/trace-annotation/src/test/java/dd/test/trace/annotation/SayTracedHello.java

@@ -34,6 +34,11 @@ public static String sayHAWithResource() {
     return "HA EARTH!!";
   }
 
+  @Trace(serviceName = "testServiceName")
+  public static String sayHelloWithServiceName() {
+    return "hello!";
+  }
+
   @Trace(operationName = "NEW_TRACE")
   public static String sayHELLOsayHA() {
     activeSpan().setTag(DDTags.SERVICE_NAME, "test2");

dd-trace-api/src/main/java/datadog/trace/api/Trace.java

@@ -16,4 +16,7 @@
 
   /** The resource name. By default it uses the same value as the operation name */
   String resourceName() default "";
+
+  /** The service name. By default it will inherit the default service name */
+  String serviceName() default "";
 }