Review fixes for jetty-8.0:javaagent (#17458)

Co-authored-by: otelbot <197425009+otelbot@users.noreply.github.com>

Author: otelbot[bot]

instrumentation/jetty/jetty-8.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jetty/v8_0/Jetty8HandlerAdvice.java

@@ -32,8 +32,7 @@ private AdviceScope(
     }
 
     @Nullable
-    public static AdviceScope start(
-        Object source, HttpServletRequest request, HttpServletResponse response) {
+    public static AdviceScope start(HttpServletRequest request, HttpServletResponse response) {
       Context attachedContext = helper().getServerContext(request);
       if (attachedContext != null) {
         // We are inside nested handler, don't create new span
@@ -63,10 +62,9 @@ public void end(
   @Advice.OnMethodEnter(suppress = Throwable.class)
   @Nullable
   public static AdviceScope onEnter(
-      @Advice.This Object source,
       @Advice.Argument(2) HttpServletRequest request,
       @Advice.Argument(3) HttpServletResponse response) {
-    return AdviceScope.start(source, request, response);
+    return AdviceScope.start(request, response);
   }
 
   @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)

instrumentation/jetty/jetty-8.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jetty/v8_0/Jetty8InstrumentationModule.java

@@ -26,6 +26,7 @@ public Jetty8InstrumentationModule() {
 
   @Override
   public ElementMatcher.Junction<ClassLoader> classLoaderMatcher() {
+    // removed in Servlet 5.0
     return hasClassesNamed("javax.servlet.Servlet");
   }
 

instrumentation/jetty/jetty-8.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jetty/v8_0/Jetty8ResponseMutator.java

@@ -8,7 +8,7 @@
 import io.opentelemetry.javaagent.bootstrap.http.HttpServerResponseMutator;
 import javax.servlet.http.HttpServletResponse;
 
-public class Jetty8ResponseMutator implements HttpServerResponseMutator<HttpServletResponse> {
+final class Jetty8ResponseMutator implements HttpServerResponseMutator<HttpServletResponse> {
   @Override
   public void appendHeader(HttpServletResponse response, String name, String value) {
     response.addHeader(name, value);

instrumentation/jetty/jetty-8.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jetty/v8_0/Jetty8Singletons.java

@@ -25,18 +25,18 @@ public final class Jetty8Singletons {
 
   private static final Instrumenter<
           ServletRequestContext<HttpServletRequest>, ServletResponseContext<HttpServletResponse>>
-      INSTRUMENTER =
+      instrumenter =
           AgentServletInstrumenterBuilder.<HttpServletRequest, HttpServletResponse>create()
               .addContextCustomizer(
                   (context, request, attributes) -> new AppServerBridge.Builder().init(context))
               .propagateOperationListenersToOnEnd()
               .build(INSTRUMENTATION_NAME, Servlet3Accessor.INSTANCE);
 
-  private static final JettyHelper<HttpServletRequest, HttpServletResponse> HELPER =
-      new JettyHelper<>(INSTRUMENTER, Servlet3Accessor.INSTANCE);
+  private static final JettyHelper<HttpServletRequest, HttpServletResponse> helper =
+      new JettyHelper<>(instrumenter, Servlet3Accessor.INSTANCE);
 
   public static JettyHelper<HttpServletRequest, HttpServletResponse> helper() {
-    return HELPER;
+    return helper;
   }
 
   private Jetty8Singletons() {}