Spring注入后反射的空指针异常

自动装配是在spring环境下当使用该类的实例时由spring容器完成了类的实例化过程，包括对依赖对象的实例化过程。

而通过反射创建实例时，是根据你调用的构造函数完成的实例化过程，没有容器的自动化创建实例了，所以需要自己对依赖对象进行注入。

所以依赖spring容器实例化和自己用反射实例化是两种独立的方式，不能相互渗透的。

1. 异常说明

在单元测试类中，要单独测一个类中的private方法，所以想通过反射获得此方法，解除私有限定，然后进行调用。此类为Service其中注入了许多的Mapper，因此在通过调用此私有方法的时候报了空指针异常的错误，错误如下：

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

注意最后面是由NullPointerException引起的。通过Debug进去以后发现是与数据库交互的Mapper没有注入进来。

单元测试代码如下：

    @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");
    }

此处有个知识点：在调用getDeclaredMethod()获得指定的方法时，第二个参数是方法的传参类型，包装类和其基本类型是不一样，例如下面方法为boolean，如果此时在上面 cArg[1] = Boolean.class;写为其包装类型的话，那么就会报错找不到此方法的错误

被反射的类中方法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();
            }
        }
    }

此处在Debug时发现tMemAcPmtDtlPoMapper为空。

2. 解决办法

在单元测试类中@Autowired要用的Mapper，然后通过反射获得上面方法要用到Mapper的变量，为其赋值即可

单元测试代码如下

    @Autowired
    private CheckAmsPmtAndPtsFlowServiceImpl checkAmsPmtAndPtsFlowServiceI;
    --在单元测试类中进行依赖注入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);
        --在此为反射的类进行赋值Mapper
        Field a1 = cls.getDeclaredField("tMemAcPmtDtlPoMapper");
        a1.setAccessible(true);
        a1.set(checkAmsPmtAndPtsFlowServiceI,tMemAcPmtDtlPoMapper);
        succesExitReove.invoke(checkAmsPmtAndPtsFlowServiceI,list,true,"1","1","2");
    }