can TextWebSocketFrame be declared with static and final?

Question

In Netty, send messages are like this:

channel.writeAndFlush(new TextWebSocketFrame("Operation Succeed"));

to run this code, nothing abnormal. so I think, argument from writeAndFlush can be extracted to a static and final variable like this:

public class LogicHandler extends SimpleUserEventChannelHandler<WebSocketServerProtocolHandler.HandshakeComplete> {
    static final TextWebSocketFrame SUCCEED = new TextWebSocketFrame("Operation Succeed");

    @Override
    protected void eventReceived(ChannelHandlerContext context, WebSocketServerProtocolHandler.HandshakeComplete arg) {
        context.channel().writeAndFlush(SUCCEED.retain()); // the client received empty content
    } 
}

to run this codes, abnormal things happen:

the client(WebSocket from Chrome browser) received the message but empty content

Are there any ideas that i can do with it?

remove the method "retain" can not solve the problem, the only way is to remove static and final keyword.

Then why not remove static/final if that works? Not sure why you use retain, this comment gives some explanation: stackoverflow.com/a/52884904/18703 — Hace
– Hace, Commented Dec 9, 2022 at 7:39
take more usage and be more effective. i also tried ReferenceCountUtil.retain(message) but no use. retain method just change the internal value of its self, the declaration seems no problem. there's a lot of scenes can be done like this. — kiki
– kiki, Commented Dec 9, 2022 at 12:58

Junyong · Accepted Answer · 2022-12-10 13:20:44Z

0

Because the underlying ByteBuf's readerIndex is updated once used. You can reuse it by reset the readerIndex, like below. But this code is thread-unsafe, it can cause problems when there are multiple connections.

public static class LogicHandler extends SimpleUserEventChannelHandler<WebSocketServerProtocolHandler.HandshakeComplete> {
    static final TextWebSocketFrame SUCCEED = new TextWebSocketFrame("Operation Succeed");

    @Override
    protected void eventReceived(ChannelHandlerContext context, WebSocketServerProtocolHandler.HandshakeComplete arg) {
        SUCCEED.content().readerIndex(0);
        context.channel().writeAndFlush(SUCCEED.retain());
    }
}

This is thread-safe

public static class LogicHandler extends SimpleUserEventChannelHandler<WebSocketServerProtocolHandler.HandshakeComplete> {
    static final TextWebSocketFrame SUCCEED = new TextWebSocketFrame("Operation Succeed");

    @Override
    protected void eventReceived(ChannelHandlerContext context, WebSocketServerProtocolHandler.HandshakeComplete arg) {
        context.channel().writeAndFlush(SUCCEED.retainedDuplicate());
    }
}

edited Dec 10, 2022 at 13:20

answered Dec 10, 2022 at 12:33

Junyong

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1 Comment

kiki Over a year ago

thx. retainedDuplicate does not work either. still it returns empty string, but readerIndex(0) real worked but thread-unsafe. i am trying to solve this

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