How to use @Inject annotation in Spring Framework for Dependency Injection ?.

@Inject annotation was introduced as JSR - 330 specification for the Dependency Injection. Its very much similar to @Autowired annotation. It doesn't have @Required attribute as @Autowired. 

Program to demonstrate how to use @Inject annotation in Spring Framework for Dependency Injection

1. A simple POJO class as Employee having Address POJO reference variable injected :

package com.hubberspot.spring.inject;

import javax.inject.Inject;



// Create a POJO class Employee which has a 
// Address Object reference as instance variable
public class Employee {

 private String name;
 private int age;

 @Inject
 private Address address;

 public Employee() {

 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 public int getAge() {
  return age;
 }

 public void setAge(int age) {
  this.age = age;
 }

 public Address getAddress() {
  return address;
 }

 public void setAddress(Address address) {
  this.address = address;
 }

}

2. Address POJO as Injected into Employee

package com.hubberspot.spring.inject;


public class Address {

 private String street;
 private String city;
 private String state;

 public Address() {

 }


 public String getStreet() {
  return street;
 }


 public void setStreet(String street) {
  this.street = street;
 }


 public String getCity() {
  return city;
 }


 public void setCity(String city) {
  this.city = city;
 }


 public String getState() {
  return state;
 }


 public void setState(String state) {
  this.state = state;
 }

}

3. Test class for testing the application :

package com.hubberspot.spring.inject;

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

public class Test {

 public static void main(String[] args) {

  // ApplicationContext is a Spring interface which 
  // provides with the configuration for an application. 
  // It provides us with all the methods that BeanFactory 
  // provides. It loads the file resources in a older 
  // and generic manner. It helps us to publish events to the
  // listener registered to it. It also provides quick support
  // for internationalization. It provides us with the object 
  // requested, it reads the configuration file and provides
  // us with the necessary object required.
  // We are using concrete implementation of ApplicationContext
  // here called as ClassPathXmlApplicationContext because this 
  // bean factory reads the xml file placed in the classpath of 
  // our application. We provide ClassPathXmlApplicationContext
  // with a configuration file called as inject.xml placed
  // at classpath of our application. 
  ApplicationContext context = 
    new ClassPathXmlApplicationContext(("inject.xml"));

  // In order to get a object instantiated for a particular bean 
  // we call getBean() method of ClassPathXmlApplicationContext
  // passing it the id for which the object is to be needed. 
  // Here getBean() returns an Object. We need to cast it back 
  // to the Employee object. Without implementing new keyword we 
  // have injected object of Employee just by reading an xml 
  // configuration file.
  Employee employee = (Employee)context.getBean("employee");

  if(employee.getAddress()==null){
   System.out.println("The Employee Name : " + employee.getName());
   System.out.println("The Employee Age : " + employee.getAge());
   System.out.println("The Employee Address : " + "is not provided");
  }
  else{
   System.out.println("The Employee Name : " + employee.getName());
   System.out.println("The Employee Age : " + employee.getAge());
   System.out.println("The Employee Address : " +   
     employee.getAddress().getStreet() + " " +
     employee.getAddress().getCity() + " " +
     employee.getAddress().getState());
  }
 }

}

4. Spring configuration file for the @Inject annotation :

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd"> <bean class="org.springframework.beans.factory. annotation.AutowiredAnnotationBeanPostProcessor"> </bean> <bean id="employee" class="com.hubberspot.spring.inject.Employee"> <property name="age" value="28" /> <property name="name" value="Jonty" /> </bean> <bean id="address" class="com.hubberspot.spring.inject.Address"> <property name="street" value="Town Hall Street" /> <property name="city" value="Pune" /> <property name="state" value="Maharashtra"></property> </bean> </beans>

Output of the program :