Scala try-catch没有捕获异常
发布时间:2020-12-16 09:50:53 所属栏目:安全 来源:网络整理
导读:据我所知,以下代码片段应该可以正常执行.流(“A”,“”).toIterable.map(_.head)抛出异常,应该由try块捕获. import org.scalatest.FunSuiteclass TryCatchTest extends FunSuite { test("Try failure") { List(1).flatMap { _ = try { Stream("A","").toIter
据我所知,以下代码片段应该可以正常执行.流(“A”,“”).toIterable.map(_.head)抛出异常,应该由try块捕获.
import org.scalatest.FunSuite class TryCatchTest extends FunSuite { test("Try failure") { List(1).flatMap { _ => try { Stream("A","").toIterable.map(_.head) } catch { case e: Throwable => Nil } } } } 但是当我运行它时,崩溃时出现以下错误: next on empty iterator java.util.NoSuchElementException: next on empty iterator at scala.collection.Iterator$$anon$2.next(Iterator.scala:39) at scala.collection.Iterator$$anon$2.next(Iterator.scala:37) at scala.collection.IndexedSeqLike$Elements.next(IndexedSeqLike.scala:63) at scala.collection.IterableLike$class.head(IterableLike.scala:107) at scala.collection.immutable.StringOps.scala$collection$IndexedSeqOptimized$$super$head(StringOps.scala:30) at scala.collection.IndexedSeqOptimized$class.head(IndexedSeqOptimized.scala:126) at scala.collection.immutable.StringOps.head(StringOps.scala:30) at TryCatchTest$$anonfun$1$$anonfun$apply$mcV$sp$1$$anonfun$apply$1.apply(TryCatchTest.scala:8) at TryCatchTest$$anonfun$1$$anonfun$apply$mcV$sp$1$$anonfun$apply$1.apply(TryCatchTest.scala:8) at scala.collection.immutable.Stream$$anonfun$map$1.apply(Stream.scala:418) at scala.collection.immutable.Stream$$anonfun$map$1.apply(Stream.scala:418) at scala.collection.immutable.Stream$Cons.tail(Stream.scala:1222) at scala.collection.immutable.Stream$Cons.tail(Stream.scala:1212) at scala.collection.immutable.Stream.foreach(Stream.scala:595) at scala.collection.immutable.List.flatMap(List.scala:327) at TryCatchTest$$anonfun$1.apply$mcV$sp(TryCatchTest.scala:5) at TryCatchTest$$anonfun$1.apply(TryCatchTest.scala:5) at TryCatchTest$$anonfun$1.apply(TryCatchTest.scala:5) at org.scalatest.Transformer$$anonfun$apply$1.apply$mcV$sp(Transformer.scala:22) at org.scalatest.OutcomeOf$class.outcomeOf(OutcomeOf.scala:85) at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104) at org.scalatest.Transformer.apply(Transformer.scala:22) at org.scalatest.Transformer.apply(Transformer.scala:20) at org.scalatest.FunSuiteLike$$anon$1.apply(FunSuiteLike.scala:166) at org.scalatest.Suite$class.withFixture(Suite.scala:1122) at org.scalatest.FunSuite.withFixture(FunSuite.scala:1555) at org.scalatest.FunSuiteLike$class.invokeWithFixture$1(FunSuiteLike.scala:163) at org.scalatest.FunSuiteLike$$anonfun$runTest$1.apply(FunSuiteLike.scala:175) at org.scalatest.FunSuiteLike$$anonfun$runTest$1.apply(FunSuiteLike.scala:175) at org.scalatest.SuperEngine.runTestImpl(Engine.scala:306) at org.scalatest.FunSuiteLike$class.runTest(FunSuiteLike.scala:175) at org.scalatest.FunSuite.runTest(FunSuite.scala:1555) at org.scalatest.FunSuiteLike$$anonfun$runTests$1.apply(FunSuiteLike.scala:208) at org.scalatest.FunSuiteLike$$anonfun$runTests$1.apply(FunSuiteLike.scala:208) at org.scalatest.SuperEngine$$anonfun$traverseSubNodes$1$1.apply(Engine.scala:413) at org.scalatest.SuperEngine$$anonfun$traverseSubNodes$1$1.apply(Engine.scala:401) at scala.collection.immutable.List.foreach(List.scala:381) at org.scalatest.SuperEngine.traverseSubNodes$1(Engine.scala:401) at org.scalatest.SuperEngine.org$scalatest$SuperEngine$$runTestsInBranch(Engine.scala:396) at org.scalatest.SuperEngine.runTestsImpl(Engine.scala:483) at org.scalatest.FunSuiteLike$class.runTests(FunSuiteLike.scala:208) at org.scalatest.FunSuite.runTests(FunSuite.scala:1555) at org.scalatest.Suite$class.run(Suite.scala:1424) at org.scalatest.FunSuite.org$scalatest$FunSuiteLike$$super$run(FunSuite.scala:1555) at org.scalatest.FunSuiteLike$$anonfun$run$1.apply(FunSuiteLike.scala:212) at org.scalatest.FunSuiteLike$$anonfun$run$1.apply(FunSuiteLike.scala:212) at org.scalatest.SuperEngine.runImpl(Engine.scala:545) at org.scalatest.FunSuiteLike$class.run(FunSuiteLike.scala:212) at org.scalatest.FunSuite.run(FunSuite.scala:1555) at org.scalatest.tools.SuiteRunner.run(SuiteRunner.scala:55) at org.scalatest.tools.Runner$$anonfun$doRunRunRunDaDoRunRun$3.apply(Runner.scala:2563) at org.scalatest.tools.Runner$$anonfun$doRunRunRunDaDoRunRun$3.apply(Runner.scala:2557) at scala.collection.immutable.List.foreach(List.scala:381) at org.scalatest.tools.Runner$.doRunRunRunDaDoRunRun(Runner.scala:2557) at org.scalatest.tools.Runner$$anonfun$runOptionallyWithPassFailReporter$2.apply(Runner.scala:1044) at org.scalatest.tools.Runner$$anonfun$runOptionallyWithPassFailReporter$2.apply(Runner.scala:1043) at org.scalatest.tools.Runner$.withClassLoaderAndDispatchReporter(Runner.scala:2722) at org.scalatest.tools.Runner$.runOptionallyWithPassFailReporter(Runner.scala:1043) at org.scalatest.tools.Runner$.run(Runner.scala:883) at org.scalatest.tools.Runner.run(Runner.scala) at org.jetbrains.plugins.scala.testingSupport.scalaTest.ScalaTestRunner.runScalaTest2(ScalaTestRunner.java:138) at org.jetbrains.plugins.scala.testingSupport.scalaTest.ScalaTestRunner.main(ScalaTestRunner.java:28) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140) 有趣的是,如果我做出以下任何更改,它将按预期运行: >用地图替换flatMap 解决方法
问题是来自Stream / Iterable的延迟评估.如果你将它分解成更小的部分,这很容易看出来.
scala> Stream("A","").toIterable.map(_.head) res7: Iterable[Char] = Stream(A,?) 将Stream映射到_.head意味着我们将字符串视为集合,而空字符串作为集合没有头,因此它将抛出异常.但是它不会立即抛出异常,因为Iterable仍然像Stream一样懒惰,如上所示.只评估第一个元素.如果我们使它非惰性,它会抛出异常: scala> Stream("A","").toIterable.map(_.head) java.util.NoSuchElementException: next on empty iterator 或者,如果用“”替换“A”,您也会得到一个例外,因为Stream的头部被计算并映射到head,而没有. scala> Stream("","").toIterable.map(_.head).toList java.util.NoSuchElementException: next on empty iterator 代码中捕获的唯一例外是当Stream或Iterable的头部抛出它时.好的,那么为什么map不抛出异常,但是flatMap呢?好吧,这张地图实际上并没有对Stream做任何事情: scala> List(1).map { _ => Stream("A","").toIterable.map(_.head) } res11: List[Iterable[Char]] = List(Stream(A,?)) 因此,未被评估的成员保持不变.但是flatMap会尝试将Iterables压缩成一个集合,因此必须对它们进行评估以制作新的集合.在这样做时,抛出异常: scala> List(1).flatMap { _ => Stream("A","").toIterable.map(_.head) } java.util.NoSuchElementException: next on empty iterator (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |