空指针异常：java.lang.NullPointerException: Cannot invoke “Object.getClass()“ because “obj“ is null

目录

问题：

java.lang.NullPointerException: Cannot invoke “Object.getClass()” because “obj” is null
    at java.base/java.lang.reflect.Method.invoke(Method.java:570)
    at org.myspringframework.core.ClassPathXmlApplicationContext.lambda$new$0(ClassPathXmlApplicationContext.java:172)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.myspringframework.core.ClassPathXmlApplicationContext.lambda$new$1(ClassPathXmlApplicationContext.java:83)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.myspringframework.core.ClassPathXmlApplicationContext.lambda$new$2(ClassPathXmlApplicationContext.java:69)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.myspringframework.core.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:43)
    at com.dong.myspring.Test.Test.main(Test.java:10)

问题指向： 

 解决：

该问题是在一个空对象上调用方法而导致的，所以增加一个非空判断即可

 if (singletonObject.get(ref) != null) {
 setMethod.invoke(singletonObject.get(id), singletonObject.get(ref));
  }

运行正常：