I recognized a huge difference between the ApplicationContext and the XmlBeanFactory regarding to the runtime initialization of the objects.
The applicationcontext calls the object constructors immediatly thus creating the objects at once.
The XmlBeanFactory creates an object only if the beanFactory.getBean(String name) is called.
If this is important for the problem domain give the following code a try as an equivalent to the origin source avoiding XmlBeanFactory.
final Resource resource = new ClassPathResource("SpringHelloWorld.xml");
final DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
final XmlBeanDefinitionReader xmlBeanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
xmlBeanDefinitionReader.loadBeanDefinitions(resource);
Spring3HelloWorld myBean = beanFactory.getBean("Spring3HelloWorldBean", Spring3HelloWorld.class);
myBean.sayHello();
To make Captain Obvious satisfied a full example with comparasion follows.
First there is the model Person.java.
package com.stackoverflow.questions_5231371;
// ./spring-tutorial/src/main/java/com/stackoverflow/questions_5231371/Person.java
public class Person {
int id;
String name;
public Person() {
System.out.println("calling Employee constructor");
}
public int getId() {
return id;
}
public void setId(final int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(final String name) {
this.name = name;
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + "]";
}
}
Then the object data in the personbeans.xml.
<?xml version="1.0" encoding="UTF-8"?>
<!-- ./spring-tutorial/src/main/java/personbeans.xmlxml -->
<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="p1" class="com.stackoverflow.questions_5231371.Person">
<property name="id" value="1" />
<property name="name" value="Sheldon" />
</bean>
<bean id="p2" class="com.stackoverflow.questions_5231371.Person">
<property name="id" value="2" />
<property name="name" value="Penny" />
</bean>
<bean id="p3" class="com.stackoverflow.questions_5231371.Person">
<property name="id" value="3" />
<property name="name" value="Leonard" />
</bean>
</beans>
And the main method who calls the objects.
package com.stackoverflow.questions_5231371;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
// ./spring-tutorial/src/main/java/com/stackoverflow/questions_5231371/Main.java
public class Main {
public static void main(final String[] args) {
// Spring #1 IoC application context
System.out.println("--- ApplicationContext");
final ApplicationContext context = new ClassPathXmlApplicationContext("personbeans.xml");
System.out.println("context created ---");
System.out.println(context.getBean("p1"));
System.out.println(context.getBean("p2"));
System.out.println(context.getBean("p3"));
// Spring #2 IoC bean factory
System.out.println("--- DefaultListableBeanFactory");
final Resource resource = new ClassPathResource("personbeans.xml");
final DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
final XmlBeanDefinitionReader xmlBeanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
xmlBeanDefinitionReader.loadBeanDefinitions(resource);
System.out.println("bean definition loaded ---");
System.out.println(beanFactory.getBean("p1"));
System.out.println(beanFactory.getBean("p2"));
System.out.println(beanFactory.getBean("p3"));
}
}
The interssting part is the comparasion when the constructor is loaded with the output "calling Employee constructor" in the console output.
--- ApplicationContext
calling Employee constructor
calling Employee constructor
calling Employee constructor
context created ---
Person [id=1, name=Sheldon]
Person [id=2, name=Penny]
Person [id=3, name=Leonard]
--- DefaultListableBeanFactory
bean definition loaded ---
calling Employee constructor
Person [id=1, name=Sheldon]
calling Employee constructor
Person [id=2, name=Penny]
calling Employee constructor
Person [id=3, name=Leonard]
