add GlobalTracer support

Signed-off-by: Sergei Malafeev <sergeymalafeev@gmail.com>

README.md

@@ -19,6 +19,7 @@ pom.xml
 ### Server
 
 - Instantiate tracer
+- Optionally register tracer with GlobalTracer: `GlobalTracer.register(tracer)`
 - Create a `ServerTracingInterceptor`
 - Intercept a service
 
@@ -33,6 +34,9 @@ import io.opentracing.Tracer;
 
         private void start() throws IOException {
             ServerTracingInterceptor tracingInterceptor = new ServerTracingInterceptor(this.tracer);
+
+            // If GlobalTracer is used: 
+            // ServerTracingInterceptor tracingInterceptor = new ServerTracingInterceptor();
 
             server = ServerBuilder.forPort(port)
                 .addService(tracingInterceptor.intercept(someServiceDef))
@@ -45,6 +49,7 @@ import io.opentracing.Tracer;
 ### Client
 
 - Instantiate a tracer
+- Optionally register tracer with GlobalTracer: `GlobalTracer.register(tracer)`
 - Create a `ClientTracingInterceptor`
 - Intercept the client channel
 
@@ -64,6 +69,9 @@ import io.opentracing.Tracer;
                 .build();
 
             ClientTracingInterceptor tracingInterceptor = new ClientTracingInterceptor(this.tracer);
+
+            // If GlobalTracer is used: 
+            // ClientTracingInterceptor tracingInterceptor = new ClientTracingInterceptor();
 
             blockingStub = GreeterGrpc.newBlockingStub(tracingInterceptor.intercept(channel));
         }

pom.xml

@@ -14,7 +14,9 @@
     the License.
 
 -->
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <groupId>io.opentracing.contrib</groupId>
   <artifactId>opentracing-grpc</artifactId>
@@ -72,6 +74,12 @@
       <version>${opentracing.version}</version>
     </dependency>
 
+    <dependency>
+      <groupId>io.opentracing</groupId>
+      <artifactId>opentracing-util</artifactId>
+      <version>${opentracing.version}</version>
+    </dependency>
+
     <dependency>
       <groupId>io.opentracing</groupId>
       <artifactId>opentracing-mock</artifactId>

src/main/java/io/opentracing/contrib/grpc/ClientTracingInterceptor.java

@@ -29,6 +29,7 @@
 import io.opentracing.Tracer;
 import io.opentracing.propagation.Format;
 import io.opentracing.propagation.TextMap;
+import io.opentracing.util.GlobalTracer;
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -51,6 +52,13 @@ public class ClientTracingInterceptor implements ClientInterceptor {
   private final ActiveSpanContextSource activeSpanContextSource;
   private final ClientSpanDecorator clientSpanDecorator;
 
+  /**
+   * Instantiate interceptor using GlobalTracer to get tracer
+   */
+  public ClientTracingInterceptor() {
+    this(GlobalTracer.get());
+  }
+
   /**
    * @param tracer to use to trace requests
    */
@@ -270,7 +278,7 @@ private Span createSpanFromParent(SpanContext parentSpanContext, String operatio
    */
   public static class Builder {
 
-    private Tracer tracer;
+    private final Tracer tracer;
     private OperationNameConstructor operationNameConstructor;
     private boolean streaming;
     private boolean verbose;
@@ -279,6 +287,13 @@ public static class Builder {
     private ActiveSpanContextSource activeSpanContextSource;
     private ClientSpanDecorator clientSpanDecorator;
 
+    /**
+     * Creates a Builder using GlobalTracer to get tracer
+     */
+    public Builder() {
+      this(GlobalTracer.get());
+    }
+
     /**
      * @param tracer to use for this intercepter
      * Creates a Builder with default configuration
@@ -388,6 +403,7 @@ public enum ClientRequestAttribute {
 
   private static class NoopClientSpanDecorator implements ClientSpanDecorator {
     @Override
-    public void interceptCall(Span span, MethodDescriptor method, CallOptions callOptions) {}
+    public void interceptCall(Span span, MethodDescriptor method, CallOptions callOptions) {
+    }
   }
 }

src/main/java/io/opentracing/contrib/grpc/ServerTracingInterceptor.java

@@ -30,6 +30,7 @@
 import io.opentracing.Tracer;
 import io.opentracing.propagation.Format;
 import io.opentracing.propagation.TextMapExtractAdapter;
+import io.opentracing.util.GlobalTracer;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -49,6 +50,13 @@ public class ServerTracingInterceptor implements ServerInterceptor {
   private final Set<ServerRequestAttribute> tracedAttributes;
   private final ServerSpanDecorator serverSpanDecorator;
 
+  /**
+   * Instantiate interceptor using GlobalTracer to get tracer
+   */
+  public ServerTracingInterceptor() {
+    this(GlobalTracer.get());
+  }
+
   /**
    * @param tracer used to trace requests
    */
@@ -222,6 +230,13 @@ public static class Builder {
     private Set<ServerRequestAttribute> tracedAttributes;
     private ServerSpanDecorator serverSpanDecorator;
 
+    /**
+     * Creates a Builder using GlobalTracer to get tracer
+     */
+    public Builder() {
+      this(GlobalTracer.get());
+    }
+
     /**
      * @param tracer to use for this intercepter
      * Creates a Builder with default configuration
@@ -303,6 +318,7 @@ public enum ServerRequestAttribute {
 
   private static class NoopServerSpanDecorator implements ServerSpanDecorator {
     @Override
-    public void interceptCall(Span span, ServerCall call, Metadata headers) {}
+    public void interceptCall(Span span, ServerCall call, Metadata headers) {
+    }
   }
 }