Spring Annotations: Hello World Application

Spring supports both annotation and xml based configurations. In my previous posts, all the examples used XML based configurations. All my coming posts, exaplains annotations provided by spring.

To work with annotation, you need to add following tag in in bean configuration file.

<context:annotation-config/>

Let me explain with @Required annotation.

@Required annotation applied on bean property methods. It makes sure that bean property must be populated at configuration time, through an explicit property value in a bean definition or through autowiring.

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;

import org.springframework.beans.factory.annotation.Required;

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;
 }

 @Required
 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();
 }

}

Notify ‘setAuthor’ method, it is annotated with @Required annotation. Application must provide the author reference at the time of Book bean initialization.

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" xmlns:context="http://www.springframework.org/schema/context"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">

 <context:annotation-config />

 <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="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="osho" />
 </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();
 }
}

Run ‘HelloWorld.java’, 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]]

To confirm the usage of Required annotation, Remove the author property from book1 bean definition.

         <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" />

         </bean>

Update myConfiguration.xml file like below.

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" xmlns:context="http://www.springframework.org/schema/context"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">

 <context:annotation-config />

 <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="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" />
 </bean>

</beans>

Re run ‘HelloWorld.java’, you can able to see following error in console.

log4j:WARN No appenders could be found for logger (org.springframework.core.env.StandardEnvironment).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'book1' defined in class path resource [myConfiguration.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'author' is required for bean 'book1'
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
 at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
 at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
 at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
 at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:751)
 at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:861)
 at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541)
 at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
 at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:93)
 at com.sample.test.HelloWorld.main(HelloWorld.java:10)
Caused by: org.springframework.beans.factory.BeanInitializationException: Property 'author' is required for bean 'book1'
 at org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.postProcessPropertyValues(RequiredAnnotationBeanPostProcessor.java:156)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1219)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543)
 ... 11 more

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