简单消息处理器

这里创建一个最简单的消息处理器，getty最少要配置一个消息处理器，用于处理收发的消息，只需把处理器注册到责任链中即可

只需继承 SimpleChannelInboundHandler<T> 即可实现简单的消息处理器

示例：

import com.gettyio.core.channel.AioChannel;
import com.gettyio.core.pipeline.PipelineDirection;
import com.gettyio.core.pipeline.in.SimpleChannelInboundHandler;
public class SimpleHandler extends SimpleChannelInboundHandler<String> {
    @Override
    public void channelAdded(AioChannel aioChannel) {
        System.out.println("连接过来了");
    }
    @Override
    public void channelClosed(AioChannel aioChannel) {
        System.out.println("连接关闭了");
    }
    @Override
    public void channelRead0(AioChannel aioChannel, String str) {
        System.out.println("读取消息:" + str);
    }
    @Override
    public void exceptionCaught(AioChannel aioChannel, Throwable cause, PipelineDirection pipelineDirection) {
        System.out.println("出错了");
    }
}