loadbalancer-experimental: remove the generic load balancer factory m…

…ethods (#2865)

Motivation:

The LoadBalancerFactory has methods that are generic in type T extends
LoadBalancedConnection which are deprecated. The generic type is infectious
and doesn't serve a concrete purpose, thus why the methods are deprecated.

Modifications:

- drop support for the deprecated factory methods
- drop the generics that were required in the LoadBalancerPolicy interface

Result:

Cleaner code.

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/DefaultLoadBalancerBuilder.java

@@ -177,7 +177,23 @@ private static final class DefaultLoadBalancerFactory<ResolvedAddress, C extends
         public <T extends C> LoadBalancer<T> newLoadBalancer(String targetResource,
              Publisher<? extends Collection<? extends ServiceDiscovererEvent<ResolvedAddress>>> eventPublisher,
              ConnectionFactory<ResolvedAddress, T> connectionFactory) {
-            return new DefaultLoadBalancer<ResolvedAddress, T>(id, targetResource, eventPublisher,
+            throw new UnsupportedOperationException("Generic constructor not supported by " +
+                    DefaultLoadBalancer.class.getSimpleName());
+        }
+
+        @Override
+        public <T extends C> LoadBalancer<T> newLoadBalancer(
+                Publisher<? extends ServiceDiscovererEvent<ResolvedAddress>> eventPublisher,
+                ConnectionFactory<ResolvedAddress, T> connectionFactory) {
+            throw new UnsupportedOperationException("Generic constructor not supported by " +
+                    DefaultLoadBalancer.class.getSimpleName());
+        }
+
+        @Override
+        public LoadBalancer<C> newLoadBalancer(
+                Publisher<? extends Collection<? extends ServiceDiscovererEvent<ResolvedAddress>>> eventPublisher,
+                ConnectionFactory<ResolvedAddress, C> connectionFactory, String targetResource) {
+            return new DefaultLoadBalancer<>(id, targetResource, eventPublisher,
                     loadBalancingPolicy.buildSelector(Collections.emptyList(), targetResource), connectionFactory,
                     linearSearchSpace, loadBalancerObserver, healthCheckConfig, healthCheckerFactory);
         }

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/LoadBalancingPolicy.java

@@ -36,8 +36,7 @@ public interface LoadBalancingPolicy<ResolvedAddress, C extends LoadBalancedConn
      * @param hosts          the set of {@link Host}s to select from.
      * @param targetResource the name of the target resource, useful for debugging purposes.
      * @return a {@link HostSelector}
-     * @param <T> the refined type of the connections over which to load balance
      */
-    <T extends C> HostSelector<ResolvedAddress, T> buildSelector(
-            List<Host<ResolvedAddress, T>> hosts, String targetResource);
+    HostSelector<ResolvedAddress, C> buildSelector(
+            List<Host<ResolvedAddress, C>> hosts, String targetResource);
 }

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/P2CLoadBalancingPolicy.java

@@ -54,8 +54,8 @@ private P2CLoadBalancingPolicy(final int maxEffort, final boolean failOpen, @Nul
     }
 
     @Override
-    public <T extends C> HostSelector<ResolvedAddress, T> buildSelector(
-            List<Host<ResolvedAddress, T>> hosts, String targetResource) {
+    public HostSelector<ResolvedAddress, C> buildSelector(
+            List<Host<ResolvedAddress, C>> hosts, String targetResource) {
         return new P2CSelector<>(hosts, targetResource, maxEffort, failOpen, random);
     }
 

servicetalk-loadbalancer-experimental/src/main/java/io/servicetalk/loadbalancer/RoundRobinLoadBalancingPolicy.java

@@ -37,8 +37,8 @@ private RoundRobinLoadBalancingPolicy(final boolean failOpen) {
     }
 
     @Override
-    public <T extends C> HostSelector<ResolvedAddress, T>
-    buildSelector(final List<Host<ResolvedAddress, T>> hosts, final String targetResource) {
+    public HostSelector<ResolvedAddress, C>
+    buildSelector(final List<Host<ResolvedAddress, C>> hosts, final String targetResource) {
         return new RoundRobinSelector<>(hosts, targetResource, failOpen);
     }
 

servicetalk-loadbalancer-experimental/src/test/java/io/servicetalk/loadbalancer/DefaultLoadBalancerTest.java

@@ -279,8 +279,8 @@ public String name() {
         }
 
         @Override
-        public <T extends TestLoadBalancedConnection> HostSelector<String, T> buildSelector(
-                List<Host<String, T>> hosts, String targetResource) {
+        public HostSelector<String, TestLoadBalancedConnection> buildSelector(
+                List<Host<String, TestLoadBalancedConnection>> hosts, String targetResource) {
             return new TestSelector(hosts);
         }