Spring: Autowiring by ‘constructor’

It is similar to byType, but applies to constructor arguments. If there is not exactly one bean of the constructor argument type in the container, a fatal error is raised.

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

  .........
  .........
}

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

I defined Author bean like below.

 <bean id="osho" name="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>

Notify following snippet, I specified auto wiring mode as constructor. Since Book has the constructor argument 'author' of type Author, and my configuration file also has the bean with type 'Author', spring automatically inject the property author into the bean book1.

 <bean id="book1" class="com.sample.pojo.Book" autowire="constructor">
  <property name="title" value="Vedanta An Art of Dying" />
  <property name="noOfPages" value="164" />
  <property name="price" value="90" />
 </bean>

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;
 
 public Book(Author author){
  this.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;
 }

 @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" name="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="book1" class="com.sample.pojo.Book" autowire="constructor">
  <property name="title" value="Vedanta An Art of Dying" />
  <property name="noOfPages" value="164" />
  <property name="price" value="90" />
 </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 book = context.getBean("book1", Book.class);
  
  System.out.println(book);

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

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]]

Previous                                                 Next                                                 Home