Hands-On High Performance with Spring 5

Constructor-based DI

Constructor-based DI is a design pattern to resolve the dependencies of a dependent object. In a constructor-based DI, a constructor is used to inject a dependent object. It is accomplished when the container invokes a constructor with a number of arguments.

Let's look at the following example for a constructor-based DI. In the following code, we show how to use a constructor for injecting a CustomerService object in a BankingService class:

@Componentpublic class BankingService {  private CustomerService customerService;  // Constructor based Dependency Injection  @Autowired  public BankingService(CustomerService customerService) {    this.customerService = customerService;  }  public void showCustomerAccountBalance() { customerService.showCustomerAccountBalance(); ...