Make defaultResolverFactory settable only once before use

core/src/main/java/com/datastax/oss/driver/internal/core/resolver/ResolverProvider.java

@@ -1,13 +1,16 @@
 package com.datastax.oss.driver.internal.core.resolver;
 
 import com.datastax.oss.driver.internal.core.resolver.defaultResolver.DefaultResolverFactory;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * Entry point for driver components to getting the {@link Resolver} instances. By default returns
  * instances of {@link DefaultResolverFactory}.
  */
 public class ResolverProvider {
 
+ private static boolean alreadyInUse = false;
+ private static boolean alreadySet = false;
  private static AbstractResolverFactory defaultResolverFactoryImpl = new DefaultResolverFactory();
 
  /**
@@ -16,7 +19,8 @@ public class ResolverProvider {
  * @param clazz Class that is requesting the {@link Resolver}.
  * @return new {@link Resolver}.
  */
- public static Resolver getResolver(Class<?> clazz) {
+ public static synchronized Resolver getResolver(Class<?> clazz) {
+ alreadyInUse = true;
  return defaultResolverFactoryImpl.getResolver(clazz);
  }
 
@@ -26,7 +30,20 @@ public static Resolver getResolver(Class<?> clazz) {
  *
  * @param resolverFactoryImpl new {@link Resolver} factory.
  */
- public static void setDefaultResolverFactory(AbstractResolverFactory resolverFactoryImpl) {
+ public static synchronized void setDefaultResolverFactory(
+ AbstractResolverFactory resolverFactoryImpl) {
+ if (alreadyInUse) {
+ throw new IllegalStateException(
+ "Cannot change default resolver factory: ResolverProvider has already returned "
+ + "an instance of a Resolver to use. Default resolver factory needs to be set up before first use by any "
+ + "class.");
+ }
+ if (alreadySet) {
+ throw new IllegalStateException(
+ "Cannot change default resolver factory: this method has already been called. "
+ + "You can set default resolver factory only once.");
+ }
+ alreadySet = true;
  defaultResolverFactoryImpl = resolverFactoryImpl;
  }
 }