Java 9 Dependency Injection

Constructor-based DI

Constructor-based dependency is generally used where you want to pass mandatory dependencies before the object is instantiated. It's provided by a container through a constructor with different arguments, and each represents dependency.

When a container starts, it checks wheather any constructor-based DI is defined for <bean>. It will create the dependency objects first, and then pass them to the current object's constructor. We will understand this by taking the classic example of using logging. It is good practice to put the log statement at various places in code to trace the flow of execution.

Let's say you have an EmployeeService class where you need to put a log in each of its methods. To achieve separation of concern, ...