Use lombok builder for Tracer construction.

This will work better for long-term support without breaking compatibility for adding new fields.

dd-trace-ext/src/main/java/datadog/trace/tracer/ext/Examples.java

@@ -12,7 +12,7 @@ class Examples {
   public static void test() {
     final Throwable someThrowable = null;
     // registration
-    TracerContext.registerGlobalContext(new TracerContext(new Tracer()), false);
+    TracerContext.registerGlobalContext(new TracerContext(Tracer.builder().build()), false);
 
     // scope
     final TracerContext ctx = TracerContext.getGlobalContext();

dd-trace/src/main/java/datadog/trace/tracer/Tracer.java

@@ -4,56 +4,52 @@ import datadog.trace.api.Config;
 import datadog.trace.tracer.sampling.AllSampler;
 import datadog.trace.tracer.sampling.Sampler;
 import datadog.trace.tracer.writer.Writer;
+import java.io.Closeable;
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Properties;
+import lombok.Builder;
 import lombok.extern.slf4j.Slf4j;
 
 /** A Tracer creates {@link Trace}s and holds common settings across traces. */
 @Slf4j
-public class Tracer {
+public class Tracer implements Closeable {
 
   /** Writer is an charge of reporting traces and spans to the desired endpoint */
   private final Writer writer;
+
   /** Sampler defines the sampling policy in order to reduce the number of traces for instance */
   private final Sampler sampler;
+
   /** Settings for this tracer. */
   private final Config config;
 
   /** Interceptors to be called on certain trace and span events */
   private final List<Interceptor> interceptors;
 
-  public Tracer() {
-    this(Config.get());
-  }
-
-  public Tracer(final List<Interceptor> interceptors) {
-    this(Config.get(), interceptors);
-  }
-
-  public Tracer(final Config config) {
-    this(config, Collections.<Interceptor>emptyList());
-  }
-
-  public Tracer(final Config config, final List<Interceptor> interceptors) {
-    // TODO: implement and include "standard" interceptors
-    this(
-        config,
-        Writer.Builder.forConfig(config),
-        new AllSampler(),
-        Collections.unmodifiableList(new ArrayList<>(interceptors)));
-  }
-
-  Tracer(
+  @Builder
+  private Tracer(
+      final String defaultServiceName,
       final Config config,
       final Writer writer,
       final Sampler sampler,
       final List<Interceptor> interceptors) {
-    this.config = config;
-    // TODO: we probably need to implement some sort of 'close' method for Tracer
-    this.writer = writer;
-    this.sampler = sampler;
-    this.interceptors = Collections.unmodifiableList(new ArrayList<>(interceptors));
+    // Apply defaults:
+    final Properties serviceNameConfig = new Properties();
+    if (defaultServiceName != null && !defaultServiceName.trim().isEmpty()) {
+      serviceNameConfig.setProperty(Config.SERVICE_NAME, defaultServiceName);
+    }
+    this.config = config != null ? config : Config.get(serviceNameConfig);
+    this.writer = writer != null ? writer : Writer.Builder.forConfig(this.config);
+    this.sampler = sampler != null ? sampler : new AllSampler();
+
+    // TODO: implement and include "standard" interceptors
+    this.interceptors =
+        interceptors != null
+            ? Collections.unmodifiableList(new ArrayList<>(interceptors))
+            : Collections.<Interceptor>emptyList();
   }
 
   /** @return {@link Writer} used by this tracer */
@@ -123,4 +119,9 @@ public class Tracer {
     log.debug(completeMessage);
     throw new TraceException(completeMessage);
   }
+
+  @Override
+  public void close() throws IOException {
+    writer.close();
+  }
 }

dd-trace/src/test/groovy/datadog/trace/tracer/TracerTest.groovy

@@ -23,7 +23,7 @@ class TracerTest extends Specification {
   // TODO: add more tests for different config options and interceptors
   def "test getters"() {
     when:
-    def tracer = new Tracer(config)
+    def tracer = Tracer.builder().config(config).build()
 
     then:
     tracer.getWriter() instanceof AgentWriter
@@ -32,9 +32,23 @@ class TracerTest extends Specification {
     tracer.getDefaultServiceName() == config.getServiceName()
   }
 
+  def "test defaultServiceName=#serviceName"() {
+    when:
+    def tracer = Tracer.builder().defaultServiceName(serviceName).build()
+
+    then:
+    tracer.config.serviceName == expected
+
+    where:
+    serviceName    | expected
+    null           | Config.DEFAULT_SERVICE_NAME
+    ""             | Config.DEFAULT_SERVICE_NAME
+    "some-service" | "some-service"
+  }
+
   def "test create current timestamp"() {
     setup:
-    def tracer = new Tracer(config)
+    def tracer = Tracer.builder().config(config).build()
 
     when:
     def timestamp = tracer.createCurrentTimestamp()
@@ -45,7 +59,7 @@ class TracerTest extends Specification {
 
   def "test trace happy path"() {
     setup:
-    def tracer = new Tracer(config, testWriter, new AllSampler(), [])
+    def tracer = Tracer.builder().config(config).writer(testWriter).build()
 
     when:
     def rootSpan = tracer.buildTrace(null)
@@ -76,7 +90,7 @@ class TracerTest extends Specification {
     //TODO implement this test properly
     setup:
     def context = Mock(SpanContext)
-    def tracer = new Tracer(config, testWriter, new AllSampler(), [])
+    def tracer = Tracer.builder().config(config).writer(testWriter).build()
 
     when:
     tracer.inject(context, null, null)
@@ -88,7 +102,7 @@ class TracerTest extends Specification {
   def "test extract"() {
     //TODO implement this test properly
     setup:
-    def tracer = new Tracer(config, testWriter, new AllSampler(), [])
+    def tracer = Tracer.builder().config(config).writer(testWriter).build()
 
     when:
     def context = tracer.extract(null, null)
@@ -100,7 +114,7 @@ class TracerTest extends Specification {
   def testReportError() {
     //TODO implement this test properly
     setup:
-    def tracer = new Tracer(config, testWriter, new AllSampler(), [])
+    def tracer = Tracer.builder().config(config).writer(testWriter).build()
 
     when:
     tracer.reportError("message %s", 123)
@@ -111,7 +125,7 @@ class TracerTest extends Specification {
 
   def "test trace that had a GCed span"() {
     setup:
-    def tracer = new Tracer(config, testWriter, new AllSampler(), [])
+    def tracer = Tracer.builder().config(config).writer(testWriter).build()
 
     when: "trace and spans get created"
     def rootSpan = tracer.buildTrace(null)
@@ -137,7 +151,7 @@ class TracerTest extends Specification {
 
   def "test trace that had a GCed continuation"() {
     setup:
-    def tracer = new Tracer(config, testWriter, new AllSampler(), [])
+    def tracer = Tracer.builder().config(config).writer(testWriter).build()
 
     when: "trace and spans get created"
     def rootSpan = tracer.buildTrace(null)