In the constructor injection, the dependency injection will be injected with the help of constructors. Now to set the dependency injection as constructor dependency injection(CDI) in bean, it is done through the bean-configuration file For this, the property to be set with the constructor dependency injection is declared under the <constructor-arg> tag in the bean-config file.
Example:
Java
package com.geeksforgeeks.org;import com.neveropen.tech.IGeek;public class GFG { // The object of the interface IGeek IGeek geek; // Constructor to set the CDI GFG(IGeek geek) { this.geek = geek; }} |
Setting the CDI in the bean-config file is as depicted through below XML file as follows:
XML
<beansxsi:schemaLocation="http://www.springframework.org/schema/beans <bean id="GFG" class="com.neveropen.tech.GFG"> <constructor-arg> <bean class="com.neveropen.tech.impl.CsvGFG" /> </constructor-arg> </bean> <bean id="CsvGFG" class="com.neveropen.tech.impl.CsvGFG" /><bean id="JsonGFG" class="com.neveropen.tech.impl.JsonGFG" /> </beans> |
Constructor injection with dependent object
If there exists a relationship between the classes of our spring application, then we create the instance of the dependent object also called the contained object. After creating the instance of the dependent object we pass it as an argument of the main class container. Example: If an employee has an address, then the instance of the address class is the dependent object.
A. Employee.java
Java
// Java Program to Illustrate Employee Classpackage com.geeksforgeeks.org;import com.neveropen.tech.Address;// Classpublic class Employee { private String name; private String employeeID; private String department; // Here 'address' is an dependent object. private Address address; // Parameterised constructor public Employee(String name, String employeeID, String department, Address address) { // this keyword refers to current instance itself this.name = name; this.employeeID = employeeID; this.department = department; this.address = (Address)address; } // Method public void display() { System.out.println("Name: " + name); System.out.println("Employee ID: " + employeeID); System.out.println("Department: " + department); System.out.println("Address: " + address); }} |
B. Address.java
Java
// Java Program to Illustrate Address Classpackage com.geeksforgeeks.org;public class Address { private String houseNo; private String pincode; private String state; private String country; // Constructor of Address Class public Address(String houseNo, String pincode, String state, String country) { // Super keyword refers to parent class super(); // This keyword refers to current instance itself this.houseNo = houseNo; this.pincode = pincode; this.state = state; this.country = country; } // Method public String toString() { return "[" + houseNo + "," + pincode + "," + state + "," + country + "]"; }} |
C. applicationContext.xml
<ref> is used to make reference to the dependent object.
XML
<?xml version="1.0" encoding="UTF-8"?> <beans xsi:schemaLocation="http://www.springframework.org/schema/beans <bean id="address1" class="com.neveropen.tech.Address"> <constructor-arg value="110/4"></constructor-arg> <constructor-arg value="123092"></constructor-arg> <constructor-arg value="Delhi"></constructor-arg> <constructor-arg value="India"></constructor-arg> </bean> <bean id="employee" class="com.neveropen.tech.Employee"> <constructor-arg value="Ram"></constructor-arg> <constructor-arg value="101"></constructor-arg> <constructor-arg value="Software testing"></constructor-arg> <constructor-arg> <ref bean="address1"/> </constructor-arg> </bean> </beans> |
D. Test.java
Java
// Java Program to Illustrate Application Classpackage com.geeksforgeeks.org;// Importing required classes from respective packagesimport org.springframework.beans.factory.BeanFactory;import org.springframework.beans.factory.xml.XmlBeanFactory;import org.springframework.core.io.ClassPathResource;import org.springframework.core.io.Resource;// Main(Application) classpublic class Test { // Main driver method public static void main(String[] args) { // Creating new class path resource Resource resource = new ClassPathResource( "applicationContext.xml"); // Creating an object of BeanFactory class BeanFactory factory = new XmlBeanFactory(resource); // Creating an object of Employee class Employee e = (Employee)factory.getBean("employee"); e.display(); }} |
Output:
Name: Ram Employee ID: 101 Department: Software testing Address: [110/4, 123092, Delhi, India]
