当我使用JUnit时，发生此错误。如何解决这个错误？

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当我使用JUnit，我碰到这个错误：当我使用JUnit时，发生此错误。如何解决这个错误？

java.lang.NullPointerException at com.mpdidb.mapper.TbUserServiceTest.selectByPrimaryKeyTest(TbUserServiceTest.java:27) 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.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:252) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94) 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$2.evaluate(ParentRunner.java:268) at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61) at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68) at com.intellij.rt.execution.junit.IdeaTestRunner$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)

，这是我的JUnit代码：

@WebAppConfiguration 
@RunWith(SpringJUnit4ClassRunner.class) 
@ContextConfiguration(classes = {RootConfig.class}) 
public class TbUserServiceTest 
{ 
    @Autowired 
    private static TbUserService tbUserService; 

    @Test 
    public void selectByPrimaryKeyTest() 
    { 
     String userId = "wusuodai"; 
     TbUser tbUser = tbUserService.selectByPrimaryKey(userId); 
     System.out.println(tbUser.getUserName()); 
    } 
}

如何解决这个问题？

来源

2017-08-02 Streamer Lee

的【什么是一个NullPointerException，如何解决呢？（可能的复制https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do- i-fix-it） – GhostCat

看起来你的@Autowired未在此设置中工作，并且tbUserService为空。老实说：如果你不知道NPE是什么以及如何处理它，那么春天和春天mvc就不是你现在可能处理的东西。而是专注于阅读一本关于java **基础的好书**。 – GhostCat

非常感谢。当我运行Web应用程序时，TbUserService可以正常运行。但是当我junit测试会遇到这个错误时，为什么会这样呢？ –

静态字段不能通过字段注入自动装配。考虑使用setter注入。

private static TbUserService tbUserService; 

@Autowired 
public void setTbUserService(TbUserService tbUserService){ 
    this.tbUserService = tbUserService; 
}

来源

2017-08-02 10:42:12 rohanagarwal

非常感谢，我解决了这个问题。 –

当我使用JUnit时，发生此错误。如何解决这个错误？

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