CODEWITHSUNDEEP
javaproject-reactor
Yohan al
Yohan al

Reputation: 31

Reactor usage of Context contextWrite / deferContextual

i could not understand why this simple code is not working. I m trying to save the initial value of my reactor Mono and reuse it later.

        Mono.just("titi caca")
                .flatMap(m -> Mono.just(m).contextWrite(context -> context.put("INITIAL", m)))
                .log()
                .flatMap(m -> Mono.just(m.toUpperCase()))
                .log()
                .flatMap(m -> Mono.<String>deferContextual(contextView -> contextView.get("INITIAL")))
                .log()
                .subscribe();

it ends with "Context does not contain key: INITIAL" ? did i completly misunderstanding this feature ?

Upvotes: 2

Views: 9421

Answers (3)

jxw
jxw

Reputation: 1

I have an example to demonstrate how to use .contextWrite(), which can run in my project

return dispatchService.requestHandWritingOcr(batchRequest)
            // get ctx
            .transformDeferredContextual((req, ctx) ->{
                System.out.println(ctx.get(Const.APPID).toString());
                System.out.println(ctx.get(Const.TRACE_ID).toString());
                return req;
            })
            // doSomething
            .map(OpenResponse::success)
            // write context on last
            .contextWrite(ctx -> {
                // context can not change, like String
                // if you put something in ctx, it will return new ctx
                // if you want it work, you need get and return new ctx
                if (StrUtil.isNotBlank(appId)) {
                    ctx = ctx.put(Const.APPID, appId);
                }
                if (StrUtil.isNotBlank(traceId)) {
                    ctx = ctx.put(Const.TRACE_ID, traceId);
                }
                return ctx;
            });

Upvotes: 0

BeCase
BeCase

Reputation: 161

First of - deferContextual() should be before contextWrite() in the code lines, as mentioned by @amanin.

Second - contextWrite() in flatMap() impact on Mono only in nested line.

If you want to pass argument to downstream, you can create object in Mono.fromCallable() or Mono.fromSupplier() or others and use it there.

See: https://projectreactor.io/docs/core/release/reference/

Upvotes: 1

rjc
rjc

Reputation: 123

Same thing happened for me when i was adding value to context in this way, but it worked when added like below :

contextWrite(Context.of("INITIAL","value") --- Working fine

contextWrite(ctx -> ctx.put("INITIAL","value")) --- Not working correctly

Upvotes: 1

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