Update the Propagators to be an actual container.

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

@@ -18,8 +18,7 @@
 
 import io.opentelemetry.context.propagation.DefaultHttpExtractor;
 import io.opentelemetry.context.propagation.DefaultHttpInjector;
-import io.opentelemetry.context.propagation.HttpExtractor;
-import io.opentelemetry.context.propagation.HttpInjector;
+import io.opentelemetry.context.propagation.Propagators;
 import io.opentelemetry.distributedcontext.CorrelationContextManager;
 import io.opentelemetry.distributedcontext.DefaultCorrelationContextManager;
 import io.opentelemetry.distributedcontext.spi.CorrelationContextManagerProvider;
@@ -53,29 +52,8 @@ public final class OpenTelemetry {
   private final TracerFactory tracerFactory;
   private final Meter meter;
   private final CorrelationContextManager contextManager;
-
-  public static final class Propagators {
-    private static volatile HttpInjector httpInjector = new DefaultHttpInjector();
-    private static volatile HttpExtractor httpExtractor = new DefaultHttpExtractor();
-
-    public static HttpExtractor getHttpExtractor() {
-      return httpExtractor;
-    }
-
-    public static void setHttpExtractor(HttpExtractor httpExtractor) {
-      Propagators.httpExtractor = httpExtractor;
-    }
-
-    public static HttpInjector getHttpInjector() {
-      return httpInjector;
-    }
-
-    public static void setHttpInjector(HttpInjector httpInjector) {
-      Propagators.httpInjector = httpInjector;
-    }
-
-    private Propagators() {}
-  }
+  private volatile Propagators propagators =
+      Propagators.create(new DefaultHttpInjector(), new DefaultHttpExtractor());
 
   /**
    * Returns a singleton {@link TracerFactory}.
@@ -113,6 +91,14 @@ public static CorrelationContextManager getCorrelationContextManager() {
     return getInstance().contextManager;
   }
 
+  public static Propagators getPropagators() {
+    return getInstance().propagators;
+  }
+
+  public static void setPropagators(Propagators propagators) {
+    getInstance().propagators = propagators;
+  }
+
   /** Lazy loads an instance. */
   private static OpenTelemetry getInstance() {
     if (instance == null) {

api/src/main/java/io/opentelemetry/context/propagation/Propagators.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.opentelemetry.context.propagation;
+
+public final class Propagators {
+  private final HttpInjector injector;
+  private final HttpExtractor extractor;
+
+  public static Propagators create(HttpInjector injector, HttpExtractor extractor) {
+    return new Propagators(injector, extractor);
+  }
+
+  private Propagators(HttpInjector injector, HttpExtractor extractor) {
+    this.injector = injector;
+    this.extractor = extractor;
+  }
+
+  public HttpExtractor getHttpExtractor() {
+    return extractor;
+  }
+
+  public HttpInjector getHttpInjector() {
+    return injector;
+  }
+}

contrib/web_servlet_filter/src/main/java/io/opentelemetry/contrib/web/servlet/filter/TracingFilter.java

@@ -20,6 +20,8 @@
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.Scope;
 import io.opentelemetry.context.propagation.ChainedPropagators;
+import io.opentelemetry.context.propagation.DefaultHttpInjector;
+import io.opentelemetry.context.propagation.Propagators;
 import io.opentelemetry.distributedcontext.propagation.DefaultCorrelationContextExtractor;
 import io.opentelemetry.trace.Span;
 import io.opentelemetry.trace.SpanContext;
@@ -145,10 +147,13 @@ public void init(FilterConfig filterConfig) throws ServletException {
       skipPattern = (Pattern) contextAttribute;
     }
 
-    // Initialize the extractor.
-    OpenTelemetry.Propagators.setHttpExtractor(
-        ChainedPropagators.chain(
-            new HttpTraceContextExtractor(), new DefaultCorrelationContextExtractor()));
+    // Initialize the propagators.
+    Propagators propagators =
+        Propagators.create(
+            new DefaultHttpInjector(),
+            ChainedPropagators.chain(
+                new HttpTraceContextExtractor(), new DefaultCorrelationContextExtractor()));
+    OpenTelemetry.setPropagators(propagators);
   }
 
   @Override
@@ -177,7 +182,8 @@ public void doFilter(
        * instance.
        */
       Context ctx =
-          OpenTelemetry.Propagators.getHttpExtractor()
+          OpenTelemetry.getPropagators()
+              .getHttpExtractor()
               .extract(Context.current(), httpRequest, HttpServletRequestGetter.getInstance());
       SpanContext extractedContext = ctx.getValue(ContextKeys.getSpanContextKey());