Spring annotations

Let’s do the previous example using annotations.

@Bean, @Configuration, and @ComponentScan

Add below maven project dependency

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.sks</groupId>
  <artifactId>spring-core-annotations-example</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  
   <properties>
  	<spring.version>5.3.0</spring.version>
  </properties>
  
  <dependencies>
  	<dependency>
  		<groupId>org.springframework</groupId>
  		<artifactId>spring-context</artifactId>
  		<version>${spring.version}</version>
  	</dependency>
  </dependencies>
  
</project>

Employee class

package com.sks;

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

public class Employee {
	
	private int id;
	private String name;
	private int age;
	private boolean contract;
	
	public Employee(int id, String name, int age, boolean contract) {
		super();
		this.id = id;
		this.name = name;
		this.age = age;
		this.contract = contract;
	}
	public Employee() {
		super();
		// TODO Auto-generated constructor stub
	}
	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", age=" + age + ", contract=" + contract + "]";
	}

}

Create configuration file

package com.sks;


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

@Configuration
@ComponentScan(basePackages = "com.sks")
public class AppConfig {

	@Bean(name = "emp")
	Employee getEmployee() {
		return new Employee();
	}
	
	@Bean(name = "emp1")
	Employee getEmployeeOne() {
		return new Employee(10,"Joe",25,true);
	}

}

Testing main class

package com.sks;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class EmployeeMain {
	
	public static void main(String[] args) {
		
		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
		
		Employee emp = (Employee) context.getBean("emp");
		Employee emp1 = (Employee) context.getBean("emp1");
		
		System.out.println("emp : " + emp);
		System.out.println("emp1 : " + emp1);
		
		context.close();
	}

}

Output :
emp : Employee [id=0, name=null, age=0, contract=false]
emp1 : Employee [id=10, name=Joe, age=25, contract=true]

@Value

This is used to give default values to the properties

Examples

	@Value("100")
	private int id;
	@Value("Mark")
	private String name;
	@Value("30")
	private int age;
	@Value("true")
	private boolean contract;

@Autowired

If there is a dependency of a custom class, such as Address class dependency in Employee class, we use @Autowired annotation.

Employee Class

package com.sks;

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

public class Employee {
	
	private int id;
	private String name;
	private int age;
	private boolean contract;
	
	@Autowired
	private Address add;
	
	public Employee(int id, String name, int age, boolean contract) {
		super();
		this.id = id;
		this.name = name;
		this.age = age;
		this.contract = contract;
	}
	
	public Employee() {
		super();
	}
	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", age=" + age + ", contract=" + contract + ", add=" + add
				+ "]";
	}
}

Address Class

package com.sks;

public class Address {
	
	private String addLine;
	private String city;
	
	public Address(String addLine, String city) {
		super();
		this.addLine = addLine;
		this.city = city;
	}
	public Address() {
		super();
	}
	@Override
	public String toString() {
		return "Address [addLine=" + addLine + ", city=" + city + "]";
	}	
}

Define a bean of Address class in AppConfig java class

package com.sks;


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

@Configuration
@ComponentScan(basePackages = "com.sks")
public class AppConfig {

	@Bean(name = "emp")
	Employee getEmployee() {
		return new Employee();
	}
	
	@Bean(name = "emp1")
	Employee getEmployeeOne() {
		return new Employee(10,"Joe",25,true);
	}
	
	@Bean(name = "add")
	Address getAddress() {
		return new Address("Street No 1","London");
	}

}

@Scope

@Scope is used to define the scope of a bean.

@Bean(name = "emp")
	@Scope(value = ConfigurableBeanFactory.SCOPE_SINGLETON)
	Employee getEmployee() {
		return new Employee();
	}