Spring 构造方法注入or属性注入

属性注入( Setter-based Dependency Injection)

基于setter的DI是在调用无参数构造函数或无参数静态工厂方法来实例化bean之后，通过容器调用bean上的setter方法来完成的。

构造方法注入（ Constructor-based Dependency Injection ）

基于构造函数的DI是通过容器调用带有许多参数的构造函数来完成的，每个参数代表一个依赖项

属性注入or构造方法注入？

1、对于强制依赖的使用构造方法注入

2、对于可选的使用属性注入

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 be a required dependency; however, constructor injection with programmatic validation of arguments is preferable.