Null pointer exception reflected after Spring injection

1. Exception description

In a unit test class, you need to test the private method in a class separately, so you want to get this method through reflection, release the private qualification, and then call it. This class injects many mappers into the Service, so an error of null pointer exception is reported when calling this private method. The error is as follows:

java.lang.reflect.InvocationTargetException
    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 com.suixingpay.bap.service.impl.CheckAmsPmtAndPtsFlowServiceImplTest.testInvoke(CheckAmsPmtAndPtsFlowServiceImplTest.java:78)
    at com.suixingpay.bap.service.impl.CheckAmsPmtAndPtsFlowServiceImplTest.insertByList(CheckAmsPmtAndPtsFlowServiceImplTest.java:69)
    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.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    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)
Caused by: java.lang.NullPointerException
    at com.suixingpay.bap.service.impl.CheckAmsPmtAndPtsFlowServiceImpl.succesExitReove(CheckAmsPmtAndPtsFlowServiceImpl.java:247)
    ... 36 more

Note that the last is caused by NullPointerException. After debugging, it is found that Mapper interacting with database is not injected.

The unit test code is as follows:

    @Autowired
    private CheckAmsPmtAndPtsFlowServiceImpl checkAmsPmtAndPtsFlowServiceI;
    
    @Test
    public void insertByList()
            throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException,
            NoSuchFieldException {
        List<TBapCheckResultSave>  list = new ArrayList<>();
        Class cls = Class.forName("service.impl.CheckAmsPmtAndPtsFlowServiceImpl");
        Class[] cArg = new Class[5];
        cArg[0] = List.class;
        cArg[1] = boolean.class;
        cArg[2] = String.class;
        cArg[3] = String.class;
        cArg[4] = String.class;
        Method succesExitReove = cls.getDeclaredMethod("succesExitReove",cArg);
        succesExitReove.setAccessible(true);
        succesExitReove.invoke(checkAmsPmtAndPtsFlowServiceI,list,true,"1","1","2");
    }

The method succesexititreove() in the reflected class is as follows

    @Autowired
    private TMemAcPmtDtlPoMapper tMemAcPmtDtlPoMapper;
    
    private void succesExitReove(List<TBapCheckResultSave> result, boolean isFen, String sourceType, String opId, String batchId) {
        Iterator<TBapCheckResultSave> iteDownPtsNoCodeSuccces = result.iterator();
        while (iteDownPtsNoCodeSuccces.hasNext()) {
            int count;
            if (isFen) {
                count = tMemAcPmtDtlPoMapper.queryCheckFlow(bapCheckResult.getOutTransId());
            } else {
                count = tMemAcPmtDtlPoMapper.queryCheckFlow(bapCheckResult.getTransId());
            }
            bapCheckResult.setPmtCount(count);
            if (count > 0) {
                iteDownPtsNoCodeSuccces.remove();
            }
        }
    }

It is found that tmemaacpmtdtlpompper is empty during debugging.

2. Solutions

The unit test code is as follows

    @Autowired
    private CheckAmsPmtAndPtsFlowServiceImpl checkAmsPmtAndPtsFlowServiceI;
    --Dependency injection in unit test classes Mapper
    @Autowired
    private TMemAcPmtDtlPoMapper tMemAcPmtDtlPoMapper;
    
    @Test
    public void insertByList()
            throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException,
            NoSuchFieldException {
        List<TBapCheckResultSave>  list = new ArrayList<>();
        Class cls = Class.forName("service.impl.CheckAmsPmtAndPtsFlowServiceImpl");
        Class[] cArg = new Class[5];
        cArg[0] = List.class;
        cArg[1] = boolean.class;
        cArg[2] = String.class;
        cArg[3] = String.class;
        cArg[4] = String.class;
        Field a1 = cls.getDeclaredField("tMemAcPmtDtlPoMapper");
        Method succesExitReove = cls.getDeclaredMethod("succesExitReove",cArg);
        succesExitReove.setAccessible(true);
        --Assign a value here to the reflected class Mapper
        Field a1 = cls.getDeclaredField("tMemAcPmtDtlPoMapper");
        a1.setAccessible(true);
        a1.set(checkAmsPmtAndPtsFlowServiceI,tMemAcPmtDtlPoMapper);
        succesExitReove.invoke(checkAmsPmtAndPtsFlowServiceI,list,true,"1","1","2");
    }