this：FluxArraymapper：item -> item.length()
s.onNext(t)
consumer.accept(x)
调用LambdaSubscriber中consumer属性的方法
示例代码：public static void main(String[] args) { Flux<String> just = Flux.just(\"Beijing\
actual：LambdaSubscriber
fastPath()
publisher：FluxMapFuseable
actual.onSubscribe(this)
subscribe(subscriber)
subscriber：LambdaSubscriber
s.request(Long.MAX_VALUE)
CoreSubscriber subscriber = Operators.toCoreSubscriber(actual)
publisher = operator.source()
s：MapFuseableSubscriber
CorePublisher publisher = Operators.onLastAssembly(this)
调用MapFuseableSubscriber#onSubscribe()入参：ArraySubscription
s：MapFuseableSubscriberarray：FluxArray中的array
just.map(item -> item.length())
publisher：FluxArray
actual：LambdaSubscriberv：mapper.apply()方法的返回值
actual.onNext(v)
consumer：System.out::println
返回值类型：FluxMapFuseable
循环
s.request(n)
s：ArraySubscription
入参：LambdaSubscriber
publisher instanceof OptimizableOperator
构建FluxMapFuseable时，传入的是 FluxArray，保存在source属性中
调用MapFuseableSubscriber中mapper属性的方法
Y
actual：LambdaSubscriberthis：MapFuseableSubscriber
onAssembly(...)
s.onSubscribe(...)
subscriber = operator.subscribeOrReturn(subscriber)
publisher.subscribe(subscriber)
返回值类型：FluxArray。array 属性存放者序列元素。
subscribe(System.out::println)
开始
subscriber：MapFuseableSubscriber
OptimizableOperator operator = (OptimizableOperator) publisher
this：FluxMapFuseable
subscribeWith(...)
operator：FluxMapFuseable
Flux<String> just = Flux.just(\"Beijing\
actual：MapFuseableSubscriberarray：FluxArray中的array
