Revert "Upgrade to Netty 4.2.0.Final"

This reverts commit a7a80a6.

See gh-45122

Author: mhalbritter

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mongo/MongoReactiveAutoConfiguration.java

@@ -21,9 +21,7 @@
 import com.mongodb.connection.TransportSettings;
 import com.mongodb.reactivestreams.client.MongoClient;
 import io.netty.channel.EventLoopGroup;
-import io.netty.channel.IoHandlerFactory;
-import io.netty.channel.MultiThreadIoEventLoopGroup;
-import io.netty.channel.nio.NioIoHandler;
+import io.netty.channel.nio.NioEventLoopGroup;
 import io.netty.channel.socket.SocketChannel;
 import reactor.core.publisher.Flux;
 
@@ -88,7 +86,7 @@ StandardMongoClientSettingsBuilderCustomizer standardMongoSettingsCustomizer(Mon
 	}
 
 	@Configuration(proxyBeanMethods = false)
-	@ConditionalOnClass({ SocketChannel.class, MultiThreadIoEventLoopGroup.class })
+	@ConditionalOnClass({ SocketChannel.class, NioEventLoopGroup.class })
 	static class NettyDriverConfiguration {
 
 		@Bean
@@ -117,8 +115,7 @@ static final class NettyDriverMongoClientSettingsBuilderCustomizer
 		@Override
 		public void customize(Builder builder) {
 			if (!isCustomTransportConfiguration(this.settings.getIfAvailable())) {
-				IoHandlerFactory ioHandlerFactory = NioIoHandler.newFactory();
-				MultiThreadIoEventLoopGroup eventLoopGroup = new MultiThreadIoEventLoopGroup(ioHandlerFactory);
+				NioEventLoopGroup eventLoopGroup = new NioEventLoopGroup();
 				this.eventLoopGroup = eventLoopGroup;
 				builder.transportSettings(TransportSettings.nettyBuilder().eventLoopGroup(eventLoopGroup).build());
 			}

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -1646,7 +1646,7 @@ bom {
 			releaseNotes("https://github.com/neo4j/neo4j-java-driver/releases/tag/{version}")
 		}
 	}
-	library("Netty", "4.2.0.Final") {
+	library("Netty", "4.1.119.Final") {
 		prohibit {
 			contains ".Alpha"
 			contains ".Beta"