Spring: Colloborators: Dependency injection using ref element

In my previous post, I explained how to inject a bean as the value of the property of other bean using ‘ref’ attribute to <property> and <constructor-arg> tags. In this post, I am going to explain how to inject a bean into other bean using ‘ref’ element.

Ex:

<ref bean="someBean"/>

You can specify the bean by specifying any one of the attributes bean, local, or parent attributes.

Ex:

<ref bean="someBean"/>

<ref local="someBean"/>

<ref parent="someBean"/>

Specifying the bean using local attribute

If you are going to specify the bean dependency using ‘local’ attribute, then the dependent bean and its dependency must be in same xml file. The value of the bean attribute may be the same as the id attribute of the target bean, or as one of the values in the name attribute of the target bean. The local attribute on the ref element is no longer supported in the 4.0 beans xsd, So I am not going to explain about this.

Specifying the bean using bean attribute

It is same as local attribute, but it can able to inject the bean that is present in other xml file also.

Following is the complete working example.

Author.java

package com.sample.pojo;

public class Author {
 private String firstName;
 private String lastName;
 private String dateOfBirth;
 private String country;

 public String getFirstName() {
  return firstName;
 }

 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }

 public String getLastName() {
  return lastName;
 }

 public void setLastName(String lastName) {
  this.lastName = lastName;
 }

 public String getDateOfBirth() {
  return dateOfBirth;
 }

 public void setDateOfBirth(String dateOfBirth) {
  this.dateOfBirth = dateOfBirth;
 }

 public String getCountry() {
  return country;
 }

 public void setCountry(String country) {
  this.country = country;
 }

 @Override
 public String toString() {
  StringBuilder builder = new StringBuilder();
  builder.append("Author [firstName=").append(firstName).append(", lastName=").append(lastName)
    .append(", dateOfBirth=").append(dateOfBirth).append(", country=").append(country).append("]");
  return builder.toString();
 }

}

Book.java

package com.sample.pojo;

public class Book {
 private String title;
 private int noOfPages;
 private float price;
 private Author author;

 public String getTitle() {
  return title;
 }

 public void setTitle(String title) {
  this.title = title;
 }

 public int getNoOfPages() {
  return noOfPages;
 }

 public void setNoOfPages(int noOfPages) {
  this.noOfPages = noOfPages;
 }

 public float getPrice() {
  return price;
 }

 public void setPrice(float price) {
  this.price = price;
 }

 public Author getAuthor() {
  return author;
 }

 public void setAuthor(Author author) {
  this.author = author;
 }

 @Override
 public String toString() {
  StringBuilder builder = new StringBuilder();
  builder.append("Book [title=").append(title).append(", noOfPages=").append(noOfPages).append(", price=")
    .append(price).append(", author=").append(author).append("]");
  return builder.toString();
 }

}

authors.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 id="osho" class="com.sample.pojo.Author">
  <property name="firstName" value="Chandra Mohan" />
  <property name="lastName" value="Jain" />
  <property name="dateOfBirth" value="11 December 1931" />
  <property name="country" value="India" />
 </bean>

</beans>

books.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 id="book1" class="com.sample.pojo.Book">
  <property name="title" value="Vedanta An Art of Dying" />
  <property name="noOfPages" value="164" />
  <property name="price" value="90" />
  <property name="author">
   <ref bean="osho" />
  </property>
 </bean>
</beans>

HelloWorld.java

package com.sample.test;

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

import com.sample.pojo.Book;

public class HelloWorld {
 public static void main(String args[]) {
  ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "books.xml", "authors.xml" });
  
  Book book = context.getBean("book1", Book.class);
  
  System.out.println(book);

  ((ClassPathXmlApplicationContext) context).close();
 }
}

Run HelloWorld application, you can able to see following output.

Book [title=Vedanta An Art of Dying, noOfPages=164, price=90.0, author=Author [firstName=Chandra Mohan, lastName=Jain, dateOfBirth=11 December 1931, country=India]]

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