不學無數——Spring注入後反射的空指針異常

Spring注入後反射的空指針異常

自動裝配是在spring環境下當使用該類的執行個體時由spring容器完成了類的執行個體化過程，包括對依賴對象的執行個體化過程。

而通過反射建立執行個體時，是根據你調用的構造函數完成的執行個體化過程，沒有容器的自動化建立執行個體了，是以需要自己對依賴對象進行注入。

是以依賴spring容器執行個體化和自己用反射執行個體化是兩種獨立的方式，不能互相滲透的。

1. 異常說明

在單元測試類中，要單獨測一個類中的

private

方法，是以想通過反射獲得此方法，解除私有限定，然後進行調用。此類為

Service

其中注入了許多的

Mapper

，是以在通過調用此私有方法的時候報了空指針異常的錯誤，錯誤如下：

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

           

注意最後面是由

NullPointerException

引起的。通過Debug進去以後發現是與資料庫互動的

Mapper

沒有注入進來。

單元測試代碼如下：

@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");
    }

           

此處有個知識點：在調用

getDeclaredMethod()

獲得指定的方法時，第二個參數是方法的傳參類型，包裝類和其基本類型是不一樣，例如下面方法為

boolean

，如果此時在上面

cArg[1] = Boolean.class;

寫為其包裝類型的話，那麼就會報錯找不到此方法的錯誤

被反射的類中方法

succesExitReove ()

如下

@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();
            }
        }
    }

           

此處在Debug時發現

tMemAcPmtDtlPoMapper

為空。

2. 解決辦法

在單元測試類中

@Autowired

要用的Mapper，然後通過反射獲得上面方法要用到

Mapper

的變量，為其指派即可

單元測試代碼如下

@Autowired
    private CheckAmsPmtAndPtsFlowServiceImpl checkAmsPmtAndPtsFlowServiceI;
    --在單元測試類中進行依賴注入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);
        --在此為反射的類進行指派Mapper
        Field a1 = cls.getDeclaredField("tMemAcPmtDtlPoMapper");
        a1.setAccessible(true);
        a1.set(checkAmsPmtAndPtsFlowServiceI,tMemAcPmtDtlPoMapper);
        succesExitReove.invoke(checkAmsPmtAndPtsFlowServiceI,list,true,"1","1","2");
    }