Spring: Inject other beans in constructor arguments

In my previous post, I explained how to inject arguments to a constructor. There are cases, where a constructor takes other objects as arguments, By using ‘constructor-arg’ tag and ‘ref’ attribute you can specify the beans to inject as constructor arguments.

 <bean id="bookOfSecrets" class="com.sample.pojo.Book">
  <constructor-arg name="author" ref="osho" />
  <constructor-arg name="title" value="The Book Of Secrets" />
  <constructor-arg name="noOfPages" value="1152" />
  <constructor-arg name="price" value="452" />
 </bean>

Bean ‘osho’ is referenced in the bean with id ‘bookOfSecrets’.

Following is the complete working application.

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;

 Book(Author author, String title, int noOfPages, float price) {
  this.author = author;
  this.title = title;
  this.noOfPages = noOfPages;
  this.price = price;
 }

 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();
 }

}

myConfiguration.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>

 <bean id="bookOfSecrets" class="com.sample.pojo.Book">
  <constructor-arg name="author" ref="osho" />
  <constructor-arg name="title" value="The Book Of Secrets" />
  <constructor-arg name="noOfPages" value="1152" />
  <constructor-arg name="price" value="452" />
 </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[] { "myConfiguration.xml" });

  Book myBook = context.getBean("bookOfSecrets", Book.class);

  System.out.println(myBook);

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

Run ‘HelloWorld.java’, you can able to see following output.

Book [title=The Book Of Secrets, noOfPages=1152, price=452.0, author=Author [firstName=Chandra Mohan, lastName=Jain, dateOfBirth=11 December 1931, country=India]]

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