@Autowired Annotation in spring

 The @Autowired annotation provides control over where and how autowiring can be done.This annotations can be done on setter method,contructor or property.We will see each in detail with example.

@Autowired on setter methods:

By default,whereever spring containers finds @autowire notation,it autowires bean byType. You can use @Autowire annotation on setter method to get rid of <property> tag in XML configuration file.

Example:

For configuring spring in your eclipse ide please refer hello world example

1.Country.java:

This is simple pojo class having some attributes so here country has name and object of Capital class.

Create Country.java under package org.arpit.javapostsforlearning.Copy following content into Country.java.

package org.arpit.javapostsforlearning;
import org.springframework.beans.factory.annotation.Autowired;
public class Country {

    String countryName;
    Capital capital;
    public String getCountryName() {
        return countryName;
    }
    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }
    public Capital getCapital() {
        return capital;
    }
    @Autowired
    public void setCapital(Capital capital) {
        this.capital = capital;
    }
}

2.Capital.java

This is also simple pojo class having one attribute called "capitalName".

Create Capital.java under package org.arpit.javapostsforlearning.java.Above Country class contains object of this class.Copy following content into Capital.java

package org.arpit.javapostsforlearning;

public class Capital {

    String capitalName;

    public String getCapitalName() {
        return capitalName;
    }

    public void setCapitalName(String capitalName) {
        this.capitalName = capitalName;
    }
}

3.AutowiredAnnotationInSpringMain.java

This class contains main function.Create AutowiredAnnotationInSpringMain.java under package org.arpit.javapostsforlearning.Copy following content into AutowiredAnnotationInSpringMain.java

 package org.arpit.javapostsforlearning;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class AutowiredAnnotationInSpringMain{

    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext("ApplicationContext.xml");

        Country countryObj = (Country) appContext.getBean("CountryBean");
        String countryName=countryObj.getCountryName();
        Capital capital=countryObj.getCapital();
        String capitalName=capital.getCapitalName();
        System.out.println(capitalName+" is capital of "+countryName);
       
    }
}

4.ApplicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.0.xsd">
	<context:annotation-config/>
	<bean id="CountryBean" class="org.arpit.javapostsforlearning.Country">
		<property name="countryName" value="India" />
	</bean>
	<bean id="CaptialBean" class="org.arpit.javapostsforlearning.Capital">
		<property name="capitalName" value="Delhi" />
	</bean>
</beans>

As you can see there is no relationship between above two beans,but we have used @autowired annotation which will automatically wire above beans on the basis of type.

5.Run it:

When you will run above application,you will get following as output.

Delhi is capital of India

@Autowired on properties:

you can use @Autowired on property to get rid of setter method.Spring container automatically assign values to corresponding attributes.You don't need setter methods for that.Make following changes to above code:

Country.java:

package org.arpit.javapostsforlearning;
import org.springframework.beans.factory.annotation.Autowired;
public class Country {

    String countryName;

    @Autowired
    Capital capital;
    public String getCountryName() {
        return countryName;
    }
    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }
    public Capital getCapital() {
        return capital;
    }
}

Run it:

When you will run above application,you will get following as output.

Delhi is capital of India

@Autowired on Constructor:

you can use @autowired on constructor also and it will work even if you didn't define <constructor-arg> tag in XML configuration file.Make following changes to above code:

Country.java:

package org.arpit.javapostsforlearning;
import org.springframework.beans.factory.annotation.Autowired;
public class Country {

    String countryName;
    Capital capital;

    @Autowired
    public Country(String countryName, Capital capital) {
	super();
	this.countryName = countryName;
	this.capital = capital;
    }
    public String getCountryName() {
        return countryName;
    }
    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }
    public Capital getCapital() {
        return capital;
    }
}

ApplicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.0.xsd">
	<context:annotation-config/>
	<bean id="CountryBean" class="org.arpit.javapostsforlearning.Country">
		<constructor-arg index="0" type="java.lang.String" value="India" />
	</bean>
	<bean id="CaptialBean" class="org.arpit.javapostsforlearning.Capital">
		<property name="capitalName" value="Delhi" />
	</bean>
</beans>

Run it:

When you will run above application,you will get following as output.

Delhi is capital of India

@Autowired with Arugments:

By default,dependency is required in the case of @Autowired like @Required but you can turn off it by passing required=false to @Autowired as argument.

Country.java:

package org.arpit.javapostsforlearning;
import org.springframework.beans.factory.annotation.Autowired;
public class Country {

    String countryName;
    @Autowired(required=false)
    Capital capital;
    public String getCountryName() {
        return countryName;
    }
    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }
    public Capital getCapital() {
        return capital;
    }
}

Now it will run even if you don't provide capital bean in XML configuration.