Stream.anyMatch中的异常
我有一些使用java stream api的代码：
boolean isAuthorized = authorizationByTenant.stream()
.filter(auth -> auth.getTenantName().equalsIgnoreCase(tenant))
.map(auth -> auth.getAuthorizedRoutes().get(component))
.flatMap(Collection::stream)
.anyMatch(routeDefinition -> isMatchingRoute(routePath, routeDefinition));有时我会得到一个指向Exception行的anyMatch：
java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:273) ~na:na在java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197) ~na:na在java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179) ~na:na在java.base/java.util.ArrayList$ArrayListSpliterator.tryAdvance(ArrayList.java:1602) ~na:na在java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipelinejava.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:527) ~na:na在java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:513) ~na:na在java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) ~na:na在java.base/java.util.stream.MatchOps$MatchOp.evaluateSequential(MatchOps.java:230) ~na:na在java.base/java.util.stream.MatchOps$MatchOp.evaluateSequential(MatchOps在java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~na:na在java.base/java.util.stream.ReferencePipeline.anyMatch(ReferencePipeline.java:632) ~na:na在com.mycompany.routefilter.functionality.FunctionalityService.isAuthorizedRoute(FunctionalityService.java:55) ~classes中！/:1.0-快照在
我的问题是null是什么？是routeDefinition吗？为什么它会让电话失败呢？我希望如果routeDefinition为null，我的方法isMatchingRoute将返回false。
谢谢。
回答 2
Stack Overflow用户
发布于 2022-06-29 13:02:23
NullPointerException发生在您的.flatMap(Collection::stream)表达式中。
我创建了一个类似的示例，并将方法引用扩展为lambda。当导致空值时，您将看到堆栈跟踪变得更加清晰。
示例：
Stream.of("foo")
.map(foo -> (List<String>) null)
.flatMap(Collection::stream)
.anyMatch(string -> "gnarly".equals(string)); // LINE 13引向
Exception in thread "main" java.lang.NullPointerException
at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:271)
at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
at java.base/java.util.stream.Streams$StreamBuilderImpl.tryAdvance(Streams.java:397)
at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:127)
at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:502)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:488)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.MatchOps$MatchOp.evaluateSequential(MatchOps.java:230)
at java.base/java.util.stream.MatchOps$MatchOp.evaluateSequential(MatchOps.java:196)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.anyMatch(ReferencePipeline.java:528)
at Test.main(Test.java:13)当我把它替换为：
Stream.of("foo")
.map(foo -> (List<String>) null)
.flatMap(strings -> strings.stream()) // LINE 11
.anyMatch(string -> "gnarly".equals(string)); // LINE 12然后例外情况变成：
Exception in thread "main" java.lang.NullPointerException
at Test.lambda$main$1(Test.java:11)
at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:271)
at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
at java.base/java.util.stream.Streams$StreamBuilderImpl.tryAdvance(Streams.java:397)
at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:127)
at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:502)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:488)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.MatchOps$MatchOp.evaluateSequential(MatchOps.java:230)
at java.base/java.util.stream.MatchOps$MatchOp.evaluateSequential(MatchOps.java:196)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.anyMatch(ReferencePipeline.java:528)
at Test.main(Test.java:12)这里，您可以在堆栈跟踪的顶部看到真正的原因在第11行。确实有点混乱，但我想JRE不能报告在方法引用中发生的异常，其行号是准确的。
编辑:关于解决方案，我的IntelliJ建议如下：
过滤器：
.filter(Objects::nonNull)
.flatMap(Collection::stream)空的安全lambda：
.flatMap(strings -> strings != null ? strings.stream() : null)Stack Overflow用户
发布于 2022-06-29 13:14:54
您的代码在.flatMap(Collection::stream)上主要是失败的。
这主要是因为您没有在.map(auth -> auth.getAuthorizedRoutes().get(component))中处理空检查。因此，为了避免这种情况，您可以在调用平台地图之前进行筛选：
boolean isAuthorized = authorizationByTenant.stream()
.filter(auth -> auth.getTenantName().equalsIgnoreCase(tenant))
.map(auth -> auth.getAuthorizedRoutes().get(component))
.filter(auth -> auth.getAuthorizedRoutes().get(component)!= null)
.flatMap(Collection::stream)
.anyMatch(routeDefinition -> isMatchingRoute(routePath, routeDefinition));我发现的提示是基于堆栈跟踪的java.base/java.util.stream.MatchOps$MatchOp.evaluateSequential(MatchOps.java:230) ~[na:na] at行的。
MatchOps$MatchOp接受谓词，并确定源流的元素(在您的情况下是从flatMap生成的流)是否匹配谓词。因此，这证实了您的flatMap正在生成null值，而null值又会接收map调用的输入。
https://stackoverflow.com/questions/72801523
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