Spring @Autowired Annotation Example

In this article we will see how to inject beans using spring @Autowired annotation.
An @Autowired annotation can be used at a constructor, field, setter method or config method.

Define the beans to be autowired

Let’s first define few beans. Each bean is annotated with @Component.

BeanA:

package dependents;

import org.springframework.stereotype.Component;

@Component
public class BeanA {
    public BeanA() {
        System.out.println("BeanA() called");
    }
}

BeanB:

package dependents;

import org.springframework.stereotype.Component;

@Component
public class BeanB {
    public BeanB() {
        System.out.println("BeanB() called");
    }
}

BeanC:

package dependents;

import org.springframework.stereotype.Component;

@Component
public class BeanC {
    public BeanC() {
        System.out.println("BeanC() called");
    }
}

Autowire the beans using @Autowired

We will now define a bean which depends on all the above defined beans. We will use @Autowired annotation to autowire the beans at field, constructor and method level.

Config:

package config;

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

import dependents.BeanA;
import dependents.BeanB;
import dependents.BeanC;

@Component("config")
@ComponentScan(basePackageClasses = BeanA.class)
public class Config {
    private BeanC beanC;

    @Autowired
    private BeanA beanA;

    private BeanB beanB;

    @Autowired
    public Config(BeanC beanC) {
        System.out.println("Config1(BeanC beanC) called");
        this.beanC = beanC;
    }

    @Autowired
    public void setBeanB(BeanB beanB) {
        this.beanB = beanB;
    }

    public String toString() {
        return "Beans: " + beanA + beanB + beanC;
    }
}

Let’s now load the context. We just have to load Config. This in turn will load the dependent beans using the @ComponentScan.

SpringAutowiredAnnotationExample:

package com.javarticles.spring;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import config.Config;

public class SpringAutowiredAnnotationExample {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
        try {
            ctx.register(Config.class);
            ctx.refresh();
            System.out.println(ctx.getBean("config"));
        } finally {
            ctx.close();
        }
    }
}

Output:

Feb 12, 2016 11:23:13 PM org.springframework.context.annotation.AnnotationConfigApplicationContext prepareRefresh
INFO: Refreshing org.spring[email protected]7c3df479: startup date [Fri Feb 12 23:23:13 IST 2016]; root of context hierarchy
BeanC() called
Config1(BeanC beanC) called
BeanA() called
BeanB() called
Beans: [email protected]@[email protected]
Feb 12, 2016 11:23:13 PM org.springframework.context.annotation.AnnotationConfigApplicationContext doClose
INFO: Closing org.spring[email protected]7c3df479: startup date [Fri Feb 12 23:23:13 IST 2016]; root of context hierarchy

Download the source code

This was an example about spring @Autowired annotation.