netty4——is not a @Sharable handler

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State management（handler的狀態管理）

A ChannelHandler often needs to store some stateful information. The simplest and recommended approach is to use member variables:

public interface Message {     // your methods here } public class DataServerHandler extends SimpleChannelInboundHandler<Message> {     private boolean loggedIn;     @Override     public void channelRead0(ChannelHandlerContext ctx, Message message) {         Channel ch = e.getChannel();         if (message instanceof LoginMessage) {             authenticate((LoginMessage) message);             loggedIn = true;         } else (message instanceof GetDataMessage) {             if (loggedIn) {                 ch.write(fetchSecret((GetDataMessage) message));             } else {                 fail();             }         }     }     ... }

 

Because the handler instance has a state variable（狀態變數） which is dedicated（專用） to one connection, you have to create a new handler instance for each new channel to avoid a race condition（競態條件） where a unauthenticated（未驗證的） client can get the confidential（機密的） information:

 // Create a new handler instance per channel. // See ChannelInitializer.initChannel(Channel). public class DataServerInitializer extends ChannelInitializer<Channel> {     @Override     public void initChannel(Channel channel) {         channel.pipeline().addLast("handler", new DataServerHandler());     } }

is not a @Sharable handler 

當出現這樣的錯誤提示時，有兩種解決方案，要麼就是加上註解@Sharable，要麼就是每次都new一個新的handler的執行個體。

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