不學無數——Spring注入後反射的空指標異常

摘要： Spring注入後反射的空指標異常 1. 異常說明 在單元測試類中，要單獨測一個類中的private 方法，所以想通過反射獲得此方法，解除私有限定，然後進行呼叫。此類為Service 其中注入了許多的Mapper ，因此在通過呼叫此私有...

Spring注入後反射的空指標異常

1. 異常說明

在單元測試類中，要單獨測一個類中的private 方法，所以想通過反射獲得此方法，解除私有限定，然後進行呼叫。此類為Service 其中注入了許多的Mapper ，因此在通過呼叫此私有方法的時候報了空指標異常的錯誤，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。

單元測試程式碼如下：

@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：在呼叫getDeclaredMethod() 獲得指定的方法時，第二個引數是方法的傳參型別，包裝類和其基本型別是不一樣，例如下面方法為boolean ，如果此時在上面cArg[1] = Boolean.class; 寫為其包裝型別的話，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 的變數，為其賦值即可

單元測試程式碼如下

@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賦值Mapper
Field a1 = cls.getDeclaredField("tMemAcPmtDtlPoMapper");
a1.setAccessible(true);
a1.set(checkAmsPmtAndPtsFlowServiceI,tMemAcPmtDtlPoMapper);
succesExitReove.invoke(checkAmsPmtAndPtsFlowServiceI,list,true,"1","1","2");
}