kotlin协程flow retryWhen当功能函数加载失败后重试（3）

刺骨的言语ヽ痛彻心扉 2023-09-25 23:29 52阅读 0赞

import kotlinx.coroutines.delay
    import kotlinx.coroutines.flow.*
    import kotlinx.coroutines.runBlocking
    import java.lang.NullPointerException
    
    fun main(args: Array<String>) {
        runBlocking {
            load().onEach {
                if (it == null) {
                    throw NullPointerException()
                }
            }.retryWhen { cause, attempt ->
                if (cause is NullPointerException) {
                    println("重试 $attempt")
    
                    delay(1000) //延时重新尝试
                }
    
                attempt < 3
            }
                .onCompletion { println("onCompletion") }
                .collect { println("collect $it") }
        }
    }
    
    fun load() = flow {
        //生成一个概率布尔，模拟加载概率性成功与失败
        var b = Boolean.let {
            var p: Int = (Math.random() * 10).toInt() % 2
            when (p) {
                0 -> true
                1 -> false
                else -> false
            }
        }
    
        var s: String? = null
        if (b) {
            println("加载成功")
            s = "fly"
        } else {
            println("加载失败")
        }
    
        emit(s)
    }

一次性加载成功：

> 加载成功  
> collect fly  
> onCompletion

加载一次失败，重试1次成功

> 加载失败  
> 重试 0  
> 加载成功  
> collect fly  
> onCompletion

再跑，加载一次失败，重试三次失败：

> 加载失败  
> 重试 0  
> 加载失败  
> 重试 1  
> 加载失败  
> 重试 2  
> 加载失败  
> 重试 3  
> onCompletion  
> Exception in thread "main" java.lang.NullPointerException  
> at MainKt$main$1$1.invokeSuspend(Main.kt:10)  
> at MainKt$main$1$1.invoke(Main.kt)  
> at MainKt$main$1$1.invoke(Main.kt)  
> at kotlinx.coroutines.flow.FlowKt\_\_TransformKt$onEach$$inlined$unsafeTransform$1$2.emit(Emitters.kt:223)  
> at kotlinx.coroutines.flow.internal.SafeCollectorKt$emitFun$1.invoke(SafeCollector.kt:15)  
> at kotlinx.coroutines.flow.internal.SafeCollectorKt$emitFun$1.invoke(SafeCollector.kt:15)  
> at kotlinx.coroutines.flow.internal.SafeCollector.emit(SafeCollector.kt:87)  
> at kotlinx.coroutines.flow.internal.SafeCollector.emit(SafeCollector.kt:66)  
> at MainKt$load$1.invokeSuspend(Main.kt:45)  
> at MainKt$load$1.invoke(Main.kt)  
> at MainKt$load$1.invoke(Main.kt)  
> at kotlinx.coroutines.flow.SafeFlow.collectSafely(Builders.kt:61)  
> at kotlinx.coroutines.flow.AbstractFlow.collect(Flow.kt:230)  
> at kotlinx.coroutines.flow.FlowKt\_\_TransformKt$onEach$$inlined$unsafeTransform$1.collect(SafeCollector.common.kt:113)  
> at kotlinx.coroutines.flow.FlowKt\_\_ErrorsKt.catchImpl(Errors.kt:156)  
> at kotlinx.coroutines.flow.FlowKt.catchImpl(Unknown Source)  
> at kotlinx.coroutines.flow.FlowKt\_\_ErrorsKt$retryWhen$$inlined$unsafeFlow$1.collect(SafeCollector.common.kt:117)  
> at kotlinx.coroutines.flow.FlowKt\_\_ErrorsKt$retryWhen$$inlined$unsafeFlow$1$1.invokeSuspend(SafeCollector.common.kt)  
> at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)  
> at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:234)  
> at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:166)  
> at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:397)  
> at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:431)  
> at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$default(CancellableContinuationImpl.kt:420)  
> at kotlinx.coroutines.CancellableContinuationImpl.resumeUndispatched(CancellableContinuationImpl.kt:518)  
> at kotlinx.coroutines.EventLoopImplBase$DelayedResumeTask.run(EventLoop.common.kt:500)  
> at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:284)  
> at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:85)  
> at kotlinx.coroutines.BuildersKt\_\_BuildersKt.runBlocking(Builders.kt:59)  
> at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)  
> at kotlinx.coroutines.BuildersKt\_\_BuildersKt.runBlocking$default(Builders.kt:38)  
> at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)  
> at MainKt.main(Main.kt:7)

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