Autowiring in Spring Framework with Example

Autowiring

What is Autowiring?

Autowiring is a feature of the Spring Framework that allows automatic injection of bean dependencies without explicitly defining them in configuration.

Instead of writing:

<property name="engine" ref="engineBean" />

You just declare the dependency and Spring handles the wiring for you.

Key Point

Spring automatically identifies the required dependency and injects it.

It internally uses constructor or setter injection.

Only reference types (like objects/beans) can be autowired. (Not for primitives or Strings)

Reduces manual configuration and boilerplate code.

Advantages of Autowiring:

Requires less code - no need to define every ref manually.

Easier to manage dependencies in large projects.

Disadvantages:

Does not support autowiring of primitive or String values.

Less control - difficult to debug or override default behavior.

Autowiring Modes in Spring

Mode	Description
no	Default. No autowiring is done.
byName	Matches bean name with property name and injects. Uses setter internally.
byType	Injects based on data type (class/interface) of the property.
constructor	Injects via constructor using parameter types.
autodetect	First tries constructor, then byType. (Deprecated from Spring 3.0+)

Example: Using @Autowired Annotation

Let us see how annotation-based Autowiring works in a Spring Boot style configuration.

Project Structure:

com.quipoin
├── Engine.java
├── Vehicle.java
├── MyApplication.java
└── MyProgram.java

Engine.java

package com.quipoin;

public class Engine {
    private String model;
    private String capacity;

    public String getModel() { return model; }
    public void setModel(String model) { this.model = model; }

    public String getCapacity() { return capacity; }
    public void setCapacity(String capacity) { this.capacity = capacity; }
}

Vechicle.java (with @Autowired)

package com.quipoin;

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

public class Vehicle {
    private String vno;
    private String vname;
    private Engine engine;

    public String getVno() { return vno; }
    public void setVno(String vno) { this.vno = vno; }

    public String getVname() { return vname; }
    public void setVname(String vname) { this.vname = vname; }

    public Engine getEngine() { return engine; }

    @Autowired
    public void setEngine(Engine engine) {
        this.engine = engine;
    }
}

MyApplicatin.java (Java-based Config)

package com.quipoin;

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

@Configuration
public class MyApplication {

    @Bean
    public Engine e1() {
        Engine e1 = new Engine();
        e1.setModel("K10 Engine");
        e1.setCapacity("1.2hpw");
        return e1;
    }

    @Bean
    public Vehicle v1() {
        Vehicle v1 = new Vehicle();
        v1.setVno("Ka51");
        v1.setVname("Swift");
        return v1;
    }
}

MyProgram.java (Main Class)

package com.quipoin;

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

public class MyProgram {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(MyApplication.class);

        Vehicle v1 = (Vehicle) context.getBean("v1");

        System.out.println("Vehicle Number: " + v1.getVno());
        System.out.println("Vehicle Name: " + v1.getVname());
        System.out.println("Engine Model: " + v1.getEngine().getModel());
        System.out.println("Engine Capacity: " + v1.getEngine().getCapacity());
    }
}

Output:

Vehicle Number: Ka51
Vehicle Name: Swift
Engine Model: K10 Engine
Engine Capacity: 1.2hpw