Dependency Injection

• Dependency injection is used to inject one object into another object.
• There are two types of injection:-

1. Property Injection 
2. Setter Injection

Key Points:

• Partial Dependency can be achieved using setter injection but it is not possible by constructor.
• When a class has three properties with a three-argument constructor and setter methods, passing information for only one property is possible only through the corresponding setter method.

Steps to achieve dependency injection (setter or property injection):

• Create a Java project with the respective package.
• Download the Spring Jar files and add them to the build path. (Spring jar file and commons-logging jar file)
• Create a Bean Class with respect to the getter and setter method.
• Create a configuration file (XML file).
• Search for the configuration file get the bean and utilize the bean. 

Example :

package com.quipoin;

import java.util.Map;

public class Student {
	private String name;
	private int id;
	private Map<String,Integer> marks;
	private char gender;

	public void setName(String name) {
		this.name=name;
	}
	public String getName() {
		return name;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public Map<String, Integer> getMarks() {
		return marks;
	}
	public void setMarks(Map<String, Integer> marks) {
		this.marks = marks;
	}
	public char getGender() {
		return gender;
	}
	public void setGender(char gender) {
		this.gender = gender;
	}
}

Configure.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"
	xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

	<!-- bean definitions here -->
	<bean class="student.Student" name="st">
		<property name="name" value="Naveen" />
		<property name="id" value="101" />

		<property name="marks">
			<map>
				<entry key="Java" value="68" />
				<entry key="sql" value="85" />
				<entry key="Spring" value="49" />
				<entry key="jdbc" value="73" />
			</map>
		</property>

		<property name="gender" value="M" />
	</bean>
</beans>

App.java

package com.quipoin;

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

public class App {
	public static void main(String []args) {
		ApplicationContext context=new       
		                      ClassPathXmlApplicationContext("configure.xml");

		Object obj=context.getBean("st");

		Student s1=(Student)obj;

		System.out.println("Student Name:"+s1.getName());
		System.out.println("Student Id:"+s1.getId());
		System.out.println("Marks:"+s1.getMarks());
		System.out.println("Gender:"+s1.getGender());
	}
}

Output:

Student Name:Naveen
Student Id:101
Marks:{Java=68, sql=85, Spring=49, jdbc=73}
Gender:M