Creata a forwarding class for HealthCheckingLoadBalancerUtil to allow…

… existing users migrate.

services/src/main/java/io/grpc/services/HealthCheckingLoadBalancerUtil.java

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+/*
+ * Copyright 2018 The gRPC 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.grpc.services;
+
+import io.grpc.ExperimentalApi;
+import io.grpc.LoadBalancer;
+import io.grpc.LoadBalancer.Helper;
+
+/**
+ * Utility for enabling
+ * <a href="https://github.com/grpc/proposal/blob/master/A17-client-side-health-checking.md">
+ * client-side health checking</a> for {@link LoadBalancer}s.
+ *
+ * @deprecated Use {@link io.grpc.protobuf.services.HealthCheckingLoadBalancerUtil} instead.
+ */
+@Deprecated
+@ExperimentalApi("https://github.com/grpc/grpc-java/issues/5025")
+public class HealthCheckingLoadBalancerUtil {
+  private HealthCheckingLoadBalancerUtil() {
+  }
+
+  /**
+   * Creates a health-checking-capable LoadBalancer.  This method is used to implement
+   * health-checking-capable {@link io.grpc.LoadBalancer.Factory}s, which will typically written
+   * this way:
+   *
+   * <pre>
+   * public class HealthCheckingFooLbFactory extends LoadBalancer.Factory {
+   *   // This is the original balancer implementation that doesn't have health checking
+   *   private final LoadBalancer.Factory fooLbFactory;
+   *
+   *   ...
+   *
+   *   // Returns the health-checking-capable version of FooLb
+   *   public LoadBalancer newLoadBalancer(Helper helper) {
+   *     return HealthCheckingLoadBalancerUtil.newHealthCheckingLoadBalancer(fooLbFactory, helper);
+   *   }
+   * }
+   * </pre>
+   *
+   * <p>As a requirement for the original LoadBalancer, it must call
+   * {@code Helper.createSubchannel()} from the {@link Helper#getSynchronizationContext()
+   * Synchronization Context}, or {@code createSubchannel()} will throw.
+   *
+   * @param factory the original factory that implements load-balancing logic without health
+   *        checking
+   * @param helper the helper passed to the resulting health-checking LoadBalancer.
+   */
+  public static LoadBalancer newHealthCheckingLoadBalancer(
+      LoadBalancer.Factory factory, Helper helper) {
+    return io.grpc.protobuf.services.HealthCheckingLoadBalancerUtil.newHealthCheckingLoadBalancer(
+        factory, helper);
+  }
+}