Java Spring Framework is one of the most widely used frameworks in software development. Spring provides developers with many features, including Dependency Injection. In this article, we will explain the concept of Dependency Injection in detail and provide example codes on how to use it in the Spring Framework.
What is Dependency Injection?
Dependency Injection is a design pattern used to reduce dependencies between objects. This pattern allows an object to obtain other objects it needs by having them provided to it. This creates a less dependent, more flexible, and sustainable code base during the object creation process.
Spring Framework and Dependency Injection
Spring Framework considers Dependency Injection as one of its fundamental principles. Spring uses Dependency Injection to reduce dependencies between objects. This allows for less coding and fewer errors during the software development process.
Spring Framework provides two methods to implement Dependency Injection:
Constructor Injection
Constructor Injection is another method of Dependency Injection. In this method, other required objects are injected into the object’s constructor during object creation. This reduces dependencies between objects.
Example Code:
In the following example code, we create a “Customer” class and an “Order” class. The “Order” class depends on the “Customer” class, which is defined in its constructor method.
public class Customer {
private String name;
private String address;
public Customer(String name, String address) {
this.name = name;
this.address = address;
}
}
public class Order {
private int orderId;
private Customer customer;
public Order(int orderId, Customer customer) {
this.orderId = orderId;
this.customer = customer;
}
}Setter Injection
Setter Injection is another method of Dependency Injection. In this method, after an object is created, the other objects that are required are injected through a special method of the object. This reduces the dependencies between objects.
Example Code:
In the following example code, we create a “Customer” class and an “Order” class. The “Order” class is dependent on the “Customer” class. This dependency is defined through the “setCustomer” method.
public class Customer {
private String name;
private String address;
public void setName(String name) {
this.name = name;
}
public void setAddress(String address) {
this.address = address;
}
}
public class Order {
private int orderId;
private Customer customer;
public void setOrderId(int orderId) {
this.orderId = orderId;
}
public void setCustomer(Customer customer) {
this.customer = customer;
}
}