s2a: don't use reflection to load token manager (grpc#11590)

Author: rmehta19

s2a/BUILD.bazel

@@ -32,33 +32,13 @@ java_library(
 )
 
 java_library(
-    name = "token_fetcher",
-    srcs = ["src/main/java/io/grpc/s2a/internal/handshaker/tokenmanager/TokenFetcher.java"],
-    deps = [
-        ":s2a_identity",
-    ],
-)
-
-java_library(
-    name = "access_token_manager",
-    srcs = [
-        "src/main/java/io/grpc/s2a/internal/handshaker/tokenmanager/AccessTokenManager.java",
-    ],
+    name = "token_manager",
+    srcs = glob([
+        "src/main/java/io/grpc/s2a/internal/handshaker/tokenmanager/*.java",
+    ]),
     deps = [
         ":s2a_identity",
-        ":token_fetcher",
         artifact("com.google.code.findbugs:jsr305"),
-    ],
-)
-
-java_library(
-    name = "single_token_fetcher",
-    srcs = [
-        "src/main/java/io/grpc/s2a/internal/handshaker/tokenmanager/SingleTokenFetcher.java",
-    ],
-    deps = [
-        ":s2a_identity",
-        ":token_fetcher",
         artifact("com.google.guava:guava"),
     ],
 )
@@ -77,13 +57,12 @@ java_library(
         "src/main/java/io/grpc/s2a/internal/handshaker/SslContextFactory.java",
     ],
     deps = [
-        ":access_token_manager",
+        ":token_manager",
         ":common_java_proto",
         ":s2a_channel_pool",
         ":s2a_identity",
         ":s2a_java_proto",
         ":s2a_java_grpc_proto",
-        ":single_token_fetcher",
         "//api",
         "//core:internal",
         "//netty",

s2a/src/main/java/io/grpc/s2a/internal/handshaker/tokenmanager/AccessTokenManager.java

@@ -17,7 +17,6 @@
 package io.grpc.s2a.internal.handshaker.tokenmanager;
 
 import io.grpc.s2a.internal.handshaker.S2AIdentity;
-import java.lang.reflect.Method;
 import java.util.Optional;
 import javax.annotation.concurrent.ThreadSafe;
 
@@ -28,19 +27,9 @@ public final class AccessTokenManager {
 
   /** Creates an {@code AccessTokenManager} based on the environment where the application runs. */
   public static Optional<AccessTokenManager> create() {
-    Optional<?> tokenFetcher;
-    try {
-      Class<?> singleTokenFetcherClass =
-          Class.forName("io.grpc.s2a.internal.handshaker.tokenmanager.SingleTokenFetcher");
-      Method createTokenFetcher = singleTokenFetcherClass.getMethod("create");
-      tokenFetcher = (Optional) createTokenFetcher.invoke(null);
-    } catch (ClassNotFoundException e) {
-      tokenFetcher = Optional.empty();
-    } catch (ReflectiveOperationException e) {
-      throw new LinkageError(e.getMessage(), e);
-    }
+    Optional<TokenFetcher> tokenFetcher = SingleTokenFetcher.create();
     return tokenFetcher.isPresent()
-        ? Optional.of(new AccessTokenManager((TokenFetcher) tokenFetcher.get()))
+        ? Optional.of(new AccessTokenManager(tokenFetcher.get()))
         : Optional.empty();
   }