spring-boot - 如何使用Rxjava2处理列表中的null？

我有一个值列表，我将使用Rxjava2 flowable打印它的每个元素。如果值为空，则程序将打印“它为空值”。

val datas: MutableList<String?> = arrayListOf("123",null ,"test12", "teas")

Flowable
            .fromIterable(datas)
            .subscribe(
                object: FlowableSubscriber<String>{
                    override fun onComplete() {
                        println("on complete")
                    }

                    override fun onSubscribe(s: Subscription) {
                        println("on subscribe")
                    }

                    override fun onNext(t: String?) {
                        if(t==null){
                          println("it's empty value")
                        } else {
                          println("value: $t")
                        }
                    }

                    override fun onError(t: Throwable?) {
                        println("error")
                        t?.printStackTrace()
                    }

                }
            )


        while(true){}

我得到如下异常:

on subscribe
error
java.lang.NullPointerException: Iterator.next() returned a null value
    at io.reactivex.internal.operators.flowable.FlowableFromIterable$IteratorConditionalSubscription.fastPath(FlowableFromIterable.java:311)
    at io.reactivex.internal.operators.flowable.FlowableFromIterable$BaseRangeSubscription.request(FlowableFromIterable.java:122)
    at io.reactivex.internal.subscribers.BasicFuseableSubscriber.request(BasicFuseableSubscriber.java:153)
    at io.reactivex.internal.operators.flowable.FlowableFlatMapMaybe$FlatMapMaybeSubscriber.onSubscribe(FlowableFlatMapMaybe.java:107)
    at io.reactivex.internal.subscribers.BasicFuseableSubscriber.onSubscribe(BasicFuseableSubscriber.java:67)
    at io.reactivex.internal.operators.flowable.FlowableFromIterable.subscribe(FlowableFromIterable.java:66)
    at io.reactivex.internal.operators.flowable.FlowableFromIterable.subscribeActual(FlowableFromIterable.java:47)
    at io.reactivex.Flowable.subscribe(Flowable.java:14827)
    at io.reactivex.internal.operators.flowable.FlowableFilter.subscribeActual(FlowableFilter.java:37)
    at io.reactivex.Flowable.subscribe(Flowable.java:14827)
    at io.reactivex.internal.operators.flowable.FlowableFlatMapMaybe.subscribeActual(FlowableFlatMapMaybe.java:54)
    at io.reactivex.Flowable.subscribe(Flowable.java:14827)
    at TestPlay.test4(TestPlay.kt:113)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

我是反应性rxjava的新手，我需要一些专家来指导我如何处理这种情况。

我有一种情况，需要检查数据库是否不存在该记录，然后必须保存该记录。但是，当我尝试处理空值时，我遇到了如上所述的异常。

最佳答案

从RxJava2文档中:



解决方案:在迭代列表之前，应进行null检查。

关于spring-boot - 如何使用Rxjava2处理列表中的null？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/55790565/