SpringFrameworkAutowiring

 

Spring Autowiring using @Autowired Annotation

Introduction

• Wiring: Process of defining object dependencies so that Spring can auto-inject the dependent objects into the target bean.
• Types of Wiring:
  • Manual Wiring: Explicitly specifying dependencies in configuration files.
  • Autowiring: Letting Spring handle dependency injection automatically.

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Autowiring in Spring

• Autowiring in Spring allows automatic dependency injection using the @Autowired annotation.
• Spring container automatically resolves the dependencies and injects them into the appropriate beans.

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Example Use-Case for Field Injection

Below is an example where a Student class has a dependency on a Department class. We use the @Autowired annotation to inject the Department dependency automatically.

Student.java

import org.springframework.beans.factory.annotation.Autowired;  
import org.springframework.stereotype.Component;  

@Component  
public class Student {  
      
    @Autowired  
    private Department department;  
      
    public void show() {  
        System.out.println(department.getDeptName());  
    }  
}  

Department.java

import org.springframework.stereotype.Component;  

@Component  
public class Department {  
      
    public String getDeptName() {  
        return "Computer Science";  
    }  
}  

Main Class

import org.springframework.context.ApplicationContext;  
import org.springframework.context.annotation.AnnotationConfigApplicationContext;  

public class Main {  
    public static void main(String[] args) {  
        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);  
        Student student = context.getBean(Student.class);  
        student.show();  
    }  
}  

Configuration Class

import org.springframework.context.annotation.ComponentScan;  
import org.springframework.context.annotation.Configuration;  

@Configuration  
@ComponentScan("com.example")  
public class AppConfig {  
}  

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Other Ways to Autowire Components

Spring provides different ways to perform autowiring:

1. By Type (Field Injection)

   • Uses @Autowired on a class field.
   • No need for setter methods.
   • Example:

     @Autowired  
     private Department department;  
     

2. By Constructor

   • Uses @Autowired on the constructor.
   • Best practice when working with immutable dependencies.
   • Example:

     @Autowired  
     public Student(Department department) {  
         this.department = department;  
     }  
     

3. By Setter Method

   • Uses @Autowired on the setter method.
   • Example:

     @Autowired  
     public void setDepartment(Department department) {  
         this.department = department;  
     }  
     

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Conclusion

• @Autowired simplifies dependency injection in Spring.
• It supports Field Injection, Constructor Injection, and Setter Injection.
• Helps reduce boilerplate code and improves manageability.
• Works with Component Scanning and Annotation-based Configuration.

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