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:
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 the collection
Spring frameworks provide us the facility to inject collection values via constructor in our spring application. The following collections can be used inside the <constructor-arg> tag:
- list
- set
- map
Example:
1) Employee.java
Create a class Employee:
Java
package com.geeksforgeeks.org; import com.neveropen.tech.IGeek;import java.util.List; public class Employee { private String name; private String employeeID; private String department; private List<String> address; public Employee(List<String> address) { this.address = (List<String>)address; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getemployeeID() { return employeeID; } public void setemployeeID(String employeeID) { this.employeeID = employeeID; } public String getdepartment() { return department; } public void setdepartment(String department) { this.department = department; } public List<String> getAddress() { return address; } public void display() { System.out.println("Name: " + getName()); System.out.println("Employee ID: " + getEmployeeID()); System.out.println("Department: " + getDepartment()); System.out.println("Address: " + getAddress()); }} |
2) applicationContext.xml
To define the list use the list element of constructor-arg.
XML
<?xml version="1.0" encoding="UTF-8"?> <beans xsi:schemaLocation="http://www.springframework.org/schema/beans <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> <list> <value>Gurugram</value> <value>Haryana</value> <value>India</value> </list> </constructor-arg> </bean> </beans> |
3) Test.java
Testing the spring application:
Java
package com.geeksforgeeks.org; import org.springframework.beans.factory.BeanFactory;import org.springframework.beans.factory.xml.XmlBeanFactory;import org.springframework.core.io.ClassPathResource;import org.springframework.core.io.Resource; public class Test { public static void main(String[] args) { Resource resource = new ClassPathResource( "applicationContext.xml"); BeanFactory factory = new XmlBeanFactory(resource); Employee e = (Employee)factory.getBean("employee"); e.display(); }} |
Output:
Name: Ram Employee ID: 101 Department: Software testing Address: [Gurugram, Haryana, India]
