Netty入门学习（五）：Netty通过反射方式获取NioServerSocketChannel对象过程代码

清疚 2023-06-08 12:59 36阅读 0赞

##### 背景 #####

1.  在服务端使用Netty的一个标准做法：

EventLoopGroup bossGroup = new NioEventLoopGroup();
            EventLoopGroup workGroup = new NioEventLoopGroup();
    
            try{
                ServerBootstrap serverBootstrap = new ServerBootstrap();
                serverBootstrap.group(bossGroup, workGroup).channel(NioServerSocketChannel.class)
                        .handler(new LoggingHandler(LogLevel.WARN))
                        .childHandler(new MyServerInitalizer());
                ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
                channelFuture.channel().closeFuture().sync();
            } finally {
                bossGroup.shutdownGracefully();
                workGroup.shutdownGracefully();
            }

1.  Netty使用抽象类AbstractBootstrap的方法channel(NioServerSocketChannel.class)是怎么获取到NioServerSocketChannel实例的？

--------------------

##### 核心类体系结构 #####

1.  把Netty源码关于如何获取NioServerSocketChannel的实例的核心类拆解出来，结构图如下：  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L291dHNhbmRpbmc_size_16_color_FFFFFF_t_70]
2.  Channel代码

public interface Channel { }

1.  ChannelFactory代码

public interface ChannelFactory<T extends Channel>{
    
        T newChannel();
    }

1.  ReflectiveChannelFactory代码

public class ReflectiveChannelFactory<T extends Channel> implements ChannelFactory<T> {
    
        private final Class<? extends T> clazz;
    
        public ReflectiveChannelFactory(Class<? extends T> clazz) {
            if (clazz == null) {
                throw new NullPointerException("clazz");
            }
            this.clazz = clazz;
        }
    
        @Override
        public T newChannel() {
            try {
                return clazz.getConstructor().newInstance();
            } catch (Throwable t) {
                throw new ChannelException("Unable to create Channel from class " + clazz, t);
            }
        }
    
        @Override
        public String toString() {
            return StringUtil.simpleClassName(clazz) + ".class";
        }
    
    }

1.  AbstractBootstrap代码

public abstract class AbstractBootstrap<B extends AbstractBootstrap<B, C>, C extends Channel> {
    
        public volatile ChannelFactory<? extends C> channelFactory;
    
    
        public B channel(Class<? extends C> channelClass) {
            if (channelClass == null) {
                throw new NullPointerException("channelClass");
            }
            return channelFactory(new ReflectiveChannelFactory<C>(channelClass));
        }
    
        public B channelFactory(ChannelFactory<? extends C> channelFactory) {
            if (channelFactory == null) {
                throw new NullPointerException("channelFactory");
            }
            if (this.channelFactory != null) {
                throw new IllegalStateException("channelFactory set already");
            }
    
            this.channelFactory = channelFactory;
            return (B) this;
        }
    
    
    }

1.  ServerBootstrap代码

public class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel> {
        
    }

1.  ServerScoketChannel代码

public interface ServerSocketChannel extends ServerChannel { }

1.  ServerChannel代码

public interface ServerChannel extends Channel { }

1.  NioServerSocketChannel代码

public class NioServerSocketChannel implements ServerSocketChannel { }

--------------------

##### 测试 #####

1.  测试代码

public class ReflectionTest {
    
        public static void main(String[] args) {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
    
            ChannelFactory beforeChannelFactory = serverBootstrap.channelFactory;
            // null
            System.out.println(beforeChannelFactory);
    
            serverBootstrap.channel(NioServerSocketChannel.class);
            ChannelFactory afterChannelFactory = serverBootstrap.channelFactory;
    
            // NioServerSocketChannel.class
            System.out.println(afterChannelFactory);
    
            // com.slabs.netty.reflect.NioServerSocketChannel@4c873330
            ServerChannel serverChannel = serverBootstrap.channelFactory.newChannel();
    
            System.out.println(serverChannel);
    
        }
    }

1.  测试结果  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L291dHNhbmRpbmc_size_16_color_FFFFFF_t_70 1]
2.  **反射 + 泛型 + 工厂方法设计模式** 实现把NioServerSocketChannel.class类型赋值给抽象类**AbstractBootstrap**的属性**channelFactory**。
3.  关键代码：channelFactory(new ReflectiveChannelFactory(channelClass))
4.  通过channelFactory.newChannel()的方法就可以拿到：NioServerSocketChannel实例对象。
5.  通过这个反射获取NioServerSocketChannel实例的小demo,熟悉Netty的核心架构体系。

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