Bean and Bean definition

What is a bean?

Typical java bean with a unique id
In spring there are basically two types

• Singleton

One instance of the bean created and referenced each time it is requested

• Prototype (non-singleton)

New bean created each time
Same as new ClassName()

What is a bean definition?

Defines a bean for Spring to manage

Key attributes

• class (required): fully qualified java class name

• id: the unique identifier for this bean

• configuration: (singleton, init-method, etc.)

• constructor-arg: arguments to pass to the constructor at creation time

• property: arguments to pass to the bean setters at creation time

• Collaborators: other beans needed in this bean (a.k.a dependencies), specified in property or constructor-arg

Typically defined in an XML file

Sample bean definition

<bean id="exampleBean" class=”org.example.ExampleBean">
   <property name="beanOne"><ref bean="anotherExampleBean"/></property>
   <property name="beanTwo"><ref bean="yetAnotherBean"/></property>
   <property name="integerProperty"><value>1</value></property>
</bean>

public class ExampleBean {
private AnotherBean beanOne;
private YetAnotherBean beanTwo;
private int i;
public void setBeanOne(AnotherBean beanOne) {
    this.beanOne = beanOne; }
public void setBeanTwo(YetAnotherBean beanTwo) {
    this.beanTwo = beanTwo; }
public void setIntegerProperty(int i) {
    this.i = i; }
…
}