记录使用java8 stream 过程中出现的问题

╰+攻爆jí腚メ 2023-03-03 11:09 16阅读 0赞

##### 记录使用java8 stream 过程中出现的问题 #####

1.  Java8使用Optional避免空检查

错误实例代码：

List<Payment> paymentList = new ArrayList<>();
            paymentList.add(new Payment());
            String paymentName = paymentList.parallelStream()
                    .filter(Objects::nonNull)
                    .map(Payment::getPayName)
                    .findFirst()
                    .orElse(null);
    
            Assert.assertNull(paymentName);

报错信息：

java.lang.NullPointerException
    	at java.util.Objects.requireNonNull(Objects.java:203)
    	at java.util.Optional.<init>(Optional.java:96)
    	at java.util.Optional.of(Optional.java:108)
    	at java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:193)
    	at java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:190)
    	at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152)
    	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    	at java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:464)
    	at com.gridsum.zhmsapi.service.impl.ReductionServiceImpl.getReductionReason(ReductionServiceImpl.java:164)
    	at com.gridsum.zhmsapi.service.impl.ReductionServiceImpl.checkReduction(ReductionServiceImpl.java:140)
    	at com.gridsum.zhmsapi.service.impl.ReductionServiceImplTest.checkReduction(ReductionServiceImplTest.java:67)
    	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:498)
    	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:73)
    	at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:83)
    	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$2.evaluate(ParentRunner.java:268)
    	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
    
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

通过查看源码得知原因：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI0NTk4NjAx_size_16_color_FFFFFF_t_70]  
像类似的原因也有很多，例如 map、filter、reduce、collect 等使用是也需要考虑空指针异常问题。

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