com.interface21.beans.factory
Interface BeanFactory

All Known Subinterfaces:

ApplicationContext, ListableBeanFactory, WebApplicationContext

All Known Implementing Classes:

AbstractBeanFactory

public interface BeanFactory

Interface to be implemented by objects that hold a number of bean definitions, each uniquely identified by a String name. An independent instance of any of these objects can be obtained (the Prototype design pattern), or a single shared instance can be obtained (a superior alternative to the Singleton design pattern). Which type of instance will be returned depends on the bean factory configuration--the API is the same. The Singleton approach is much more useful and more common in practice.

The point of this approach is that the BeanFactory is a central registry of application components, and centralizes the configuring of application components (no more do individual objects need to read properties files, for example). See chapters 4 and 11 of "Expert One-on-One J2EE" for a discussion of the benefits of this approach.
Normally the BeanFactory will load bean definitions stored in a configuration source (such as an XML document), and uses the com.interface21.beans package to configure the beans. However, an implementation could simply return Java objects it creates as necessary directly in Java code. There are no constraints on how the definitions could be stored: LDAP, RDBMS, XML, properties file etc. Implementations are encouraged to support references amongst beans, to either Singlet5ons or Prototypes.

Since:

13 April 2001

Version:

$RevisionId$

Author:

Rod Johnson

Method Summary

java.lang.String[]	getAliases(java.lang.String name) Return the aliases for the given bean name, if defined.
java.lang.Object	getBean(java.lang.String name) Return an instance (possibly shared or independent) of the given bean name.
java.lang.Object	getBean(java.lang.String name, java.lang.Class requiredType) Return an instance (possibly shared or independent) of the given bean name.
boolean	isSingleton(java.lang.String name) Is this bean a singleton?

Method Detail

getBean

public java.lang.Object getBean(java.lang.String name)
                         throws BeansException

Return an instance (possibly shared or independent) of the given bean name. This method allows a bean factory to be used as a replacement for the Singleton or Prototype design pattern.
Note that callers should retain references to returned objects. There is no guarantee that this method will be implemented to be efficient. For example, it may be synchronized, or may need to run an RDBMS query.

Parameters:

name - name of the bean to return

Returns:

the instance of the bean

Throws:

NoSuchBeanDefinitionException - if there's no such bean definition

getBean

public java.lang.Object getBean(java.lang.String name,
                                java.lang.Class requiredType)
                         throws BeansException

Return an instance (possibly shared or independent) of the given bean name. Provides a measure of type safety by throwing an exception if the bean is not of the required type. This method allows a bean factory to be used as a replacement for the Singleton or Prototype design pattern.
Note that callers should retain references to returned objects. There is no guarantee that this method will be implemented to be efficient. For example, it may be synchronized, or may need to run an RDBMS query.

Parameters:

name - name of the bean to return

requiredType - type the bean may match. Can be an interface or superclass of the actual class. For example, if the value is Object.class, this method will succeed whatever the class of the returned instance.

Returns:

the instance of the bean

Throws:

BeanNotOfRequiredTypeException - if the bean is not of the required type

NoSuchBeanDefinitionException - if there's no such bean definition

isSingleton

public boolean isSingleton(java.lang.String name)
                    throws NoSuchBeanDefinitionException

Is this bean a singleton? That is, will getBean() always return the same object?

Parameters:

name - name of the bean to query

Returns:

is this bean a singleton

Throws:

NoSuchBeanDefinitionException - if there is no bean with the given name

getAliases

public java.lang.String[] getAliases(java.lang.String name)

Return the aliases for the given bean name, if defined.

Parameters:

name - the bean name to check for aliases

Returns:

the aliases, or an empty array if none