IM系统简介
IM（Instant Messaging，即时通讯）又叫做实时通信
IM和Netty - 客户端实现逻辑
IM和Netty - 服务端实现逻辑
Pipeline与ChannelHandler
Netty中的管道-过滤器
Channel+ChannelPipeline+ChannelHandlerContext
ChannelHandler
Netty内置ChannelHandlerAdapter
MessageToByteEncoder
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| public abstract class MessageToByteEncoder<I> extends ChannelOutboundHandlerAdapter {
protected abstract void encode(ChannelHandlerContext ctx, I msg, ByteBuf byteBuf) throws Exception;
}
public class PacketEncoder extends MessageToByteEncoder<MyMessage> {
@Override
protected void encode(ChannelHandlerContext ctx, MyMessage message, ByteBuf byteBuf) throws Exception {
//完成自定义编码
ByteBuf byteBuf = ...
}
}
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ByteToMessageDecoder
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| public abstract class ByteToMessageDecoder extends ChannelInboundHandlerAdapter {
protected abstract void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception;
}
public class PacketDecoder extends ByteToMessageDecoder {
@Override
protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List list) throws Exception {
//完成自定义解码
MyMessage message = ...;
list.add(message);
}
}
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SimpleChannelInboundHandler
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| public abstract class SimpleChannelInboundHandler<I> extends ChannelInboundHandlerAdapter {
protected abstract void channelRead0(ChannelHandlerContext ctx, I msg) throws Exception;
}
public class LoginResponseHandler extends SimpleChannelInboundHandler<MyMessage> {
@Override
protected void channelRead0(ChannelHandlerContext channelHandlerContext, MyMessage message) throws Exception {
//针对MyMessage处理登录逻辑
}
}
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AuthenticationHandler
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| public class AuthenticationHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
//如果认证通过则继续执行，否则直接断开连接
}
@Override
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
//打印日志
}
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
//执行下线
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
//异常时断开连接
}
}
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IM单聊的原理与实现
设计通信协议
为了实现定制化和扩展性，通常都需要定义一套私有协议，例如Dubbo框架
