Spring bean - 验证是否正确初始化

Question

I'm using Spring frameworks for my Java Project. When I start the module sometimes spring beans are not correctly initialized and the bean will be null and program will have exception (Null Pointer Exception) . Is there any way to make sure that during start up all the beans are initialized properly?

Answer 1

There is a @Required annotation in spring. This will make sure that the dependencies are present before initializing the beans. If the dependencies are not present it will throw error before initializing beans. Use this in your code and try again. If you are still facing issues please post your code here.

Answer 2

Since you can mix constructor-based and setter-based DI, it is a good rule of thumb to use constructors for mandatory dependencies and setter methods or configuration methods for optional dependencies. Note that use of the @Required annotation on a setter method can be used to make the property a required dependency.

The Spring team generally advocates constructor injection as it enables one to implement application components as immutable objects and to ensure that required dependencies are not null. Furthermore constructor-injected components are always returned to client (calling) code in a fully initialized state. As a side note, a large number of constructor arguments is a bad code smell, implying that the class likely has too many responsibilities and should be refactored to better address proper separation of concerns.

In that way, If your beans are immutable objects then just use constructor-based DI. If they not immutable then you can combine constructor-based and setter-based DI, or use @Required annotation.