Split global functionality into a separate class (#2233) (#2239)

This ensure clear separation of functionality. This PR does not change any functionality, it just restructures the code to separate global functionality from
the Default implementation. Also helps to ensure that Global initialization does not happen by mistake when working only with the default implementation.

Also it helps with methods like `OpenTelemetry.get()` and `OpenTelemetry.set()` to understand they are interacting with global instance

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

api/all/src/main/java/io/opentelemetry/api/DefaultOpenTelemetry.java

@@ -28,10 +28,10 @@ public class DefaultOpenTelemetry implements OpenTelemetry {
 
   private final TracerProvider tracerProvider;
   private final MeterProvider meterProvider;
-
   private volatile ContextPropagators propagators;
 
   @Override
+  @Deprecated
   public void setPropagators(ContextPropagators propagators) {
     this.propagators = propagators;
   }

api/all/src/main/java/io/opentelemetry/api/GlobalOpenTelemetry.java

@@ -158,7 +158,10 @@ public final class GlobalOpenTelemetry {
 
   /**
    * Sets the globally registered {@link ContextPropagators} for remote propagation of a context.
+   *
+   * @deprecated this will be removed soon, create a new instance if necessary.
    */
+  @Deprecated
   public static void setPropagators(ContextPropagators propagators) {
     requireNonNull(propagators, "propagators");
     get().setPropagators(propagators);

api/all/src/main/java/io/opentelemetry/api/OpenTelemetry.java

@@ -5,8 +5,6 @@
 
 package io.opentelemetry.api;
 
-import static java.util.Objects.requireNonNull;
-
 import io.opentelemetry.api.metrics.Meter;
 import io.opentelemetry.api.metrics.MeterProvider;
 import io.opentelemetry.api.trace.Tracer;
@@ -15,6 +13,7 @@ import io.opentelemetry.context.propagation.ContextPropagators;
 import io.opentelemetry.spi.OpenTelemetryFactory;
 import io.opentelemetry.spi.metrics.MeterProviderFactory;
 import io.opentelemetry.spi.trace.TracerProviderFactory;
+import java.util.Objects;
 
 /**
  * The entrypoint to telemetry functionality for tracing, metrics and baggage.
@@ -130,15 +129,20 @@ public interface OpenTelemetry {
   /**
    * Sets the globally registered {@link ContextPropagators} for remote propagation of a context.
    *
-   * @deprecated use {@link GlobalOpenTelemetry#setPropagators(ContextPropagators)}
+   * @deprecated this will be removed soon, create a new instance if necessary.
    */
   @Deprecated
   static void setGlobalPropagators(ContextPropagators propagators) {
-    requireNonNull(propagators, "propagators");
+    Objects.requireNonNull(propagators, "propagators");
     get().setPropagators(propagators);
   }
 
-  /** Sets the propagators that this instance should contain. */
+  /**
+   * Sets the propagators that this instance should contain.
+   *
+   * @deprecated this will be removed soon, create a new instance if necessary.
+   */
+  @Deprecated
   void setPropagators(ContextPropagators propagators);
 
   /** Returns the {@link TracerProvider} for this {@link OpenTelemetry}. */

api/all/src/test/java/io/opentelemetry/api/OpenTelemetryTest.java

@@ -173,6 +173,7 @@ class OpenTelemetryTest {
   }
 
   @Test
+  @SuppressWarnings("deprecation") // tested deprecated code
   void testGlobalPropagatorsSet() {
     ContextPropagators propagators = ContextPropagators.noop();
     GlobalOpenTelemetry.setPropagators(propagators);
@@ -180,6 +181,7 @@ class OpenTelemetryTest {
   }
 
   @Test
+  @SuppressWarnings("deprecation") // tested deprecated code
   void testPropagatorsSet() {
     ContextPropagators propagators = ContextPropagators.noop();
     OpenTelemetry instance = DefaultOpenTelemetry.builder().build();
@@ -237,6 +239,7 @@ class OpenTelemetryTest {
   }
 
   @Test
+  @SuppressWarnings("deprecation") // tested deprecated code
   void testPropagatorsSetNull() {
     assertThrows(NullPointerException.class, () -> GlobalOpenTelemetry.setPropagators(null));
   }

integration-tests/tracecontext/src/main/java/io/opentelemetry/Application.java

@@ -29,6 +29,7 @@ import spark.Response;
 import spark.Route;
 import spark.Spark;
 
+@SuppressWarnings("deprecation") // using deprecated code in tests
 public class Application {
   private static final Logger logger = Logger.getLogger(Application.class.getName());
   private static final OpenTelemetry openTelemetry;