Spring – Dependency Injection | Code Factory

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• Simple definition of DI is passing required parameters to POJO classes from xml.
• Dependency Injection is a fundamental aspect of the Spring framework, through which the Spring container “injects” objects into other objects or “dependencies”.
• Spring use IOC to get runtime parameters from spring.xml and pass to POJO. To receive parameters from IOC to POJO class it need to have setters method or parameterized constructor.
• * Dependency Injection (DI) Type
  • Setter based Dependency Injection
  • Constructor based Dependency Injection
  • Lookup Method Dependency Injection

Create Java Project

• Open Eclipse
• Go to File -> New -> Others… -> Java Project
• Create DI project
• Right click on project -> Build Path -> Configure Build Path -> Libraries tab -> Add External JARs
  • commons-logging-X.X.jar
  • spring-beans-X.X.X.jar
  • spring-context-X.X.X.jar
  • spring-core-X.X.X.jar
  • spring-expression-X.X.X.jar
• * You can find dtd information from spring-beans-X.X.X.jar -> org -> springframework -> beans -> factory -> xml -> spring-beans.dtd (line no 36 & 37)

spring.xml

<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN"
	"http://www.springframework.org/dtd/spring-beans-2.0.dtd">

<beans>
	<bean id="t" class="com.codeFactory.beans.Test">
		<property name="gender" value="Mr." />
	</bean>
</beans>

Test.java

package com.codeFactory.beans;

/**
 * @author code.factory
 *
 */
public class Test {

	String gender;

	public void setGender(String gender) {
		this.gender = gender;
	}

	public void hello(String name) {
		System.out.println("Hello " + gender + " " + name);
	}
}

Client.java

package com.codeFactory.test;

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

import com.codeFactory.beans.Test;

/**
 * @author code.factory
 *
 */
public class Client {
	public static void main(String... args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("com/codeFactory/resources/spring.xml");
		
		Test t = (Test) context.getBean("t");
		t.hello("CodeFactory");
	}
}

Output:

Dec 11, 2020 7:18:09 PM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@4bf558aa: startup date [Fri Dec 11 19:18:09 IST 2020]; root of context hierarchy
Dec 11, 2020 7:18:09 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [com/codeFactory/resources/spring.xml]
Hello Mr. CodeFactory