org.springframework.beans.factory
Interface BeanFactory

All Known Subinterfaces:
ApplicationContext, AutowireCapableBeanFactory, ConfigurableApplicationContext, ConfigurableBeanFactory, ConfigurableListableBeanFactory, ConfigurableWebApplicationContext, HierarchicalBeanFactory, ListableBeanFactory, WebApplicationContext
All Known Implementing Classes:
AbstractApplicationContext, AbstractAutowireCapableBeanFactory, AbstractBeanFactory, DefaultListableBeanFactory, StaticListableBeanFactory, StaticWebApplicationContext, XmlWebApplicationContext

public interface BeanFactory

The root interface for accessing a Spring IoC container.

This interface is implemented by objects that hold a number of bean definitions, each uniquely identified by a String name. Depending on the bean definition, the factory will return either an independent instance of a contained object (the Prototype design pattern), or a single shared instance (a superior alternative to the Singleton design pattern, in which the instance is a singleton in the scope of the factory). Which type of instance will be returned depends on the bean factory configuration - the API is the same. The Singleton approach is 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 configuration 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 Design and Development" for a discussion of the benefits of this approach.

Note that it is generally better to rely on Dependency Injection ("push" configuration) to configure application objects through setters or constructors, rather than use any form of "pull" configuration like a BeanFactory lookup. Spring's Dependency Injection functionality is implemented using BeanFactory and its subinterfaces.

Normally a BeanFactory will load bean definitions stored in a configuration source (such as an XML document), and use the org.springframework.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 Singletons or Prototypes.

In contrast to the methods in ListableBeanFactory, all of the methods in this interface will also check parent factories if this is a HierarchicalBeanFactory. If a bean is not found in this factory instance, the immediate parent is asked. Beans in this factory instance are supposed to override beans of the same name in any parent factory.

Bean factory implementations should support the standard bean lifecycle interfaces as far as possible. The maximum set of initialization methods and their standard order is:
1. BeanNameAware's setBeanName
2. BeanFactoryAware's setBeanFactory
3. ApplicationContextAware's setApplicationContext (only applicable if running in an application context)
4. postProcessBeforeInitialization methods of BeanPostProcessors
5. InitializingBean's afterPropertiesSet
6. a custom init-method definition
7. postProcessAfterInitialization methods of BeanPostProcessors

On shutdown of a bean factory, the following lifecycle methods apply:
1. DisposableBean's destroy
2. a custom destroy-method definition

Since:
13 April 2001
Author:
Rod Johnson, Juergen Hoeller
See Also:
BeanNameAware.setBeanName(java.lang.String), BeanFactoryAware.setBeanFactory(org.springframework.beans.factory.BeanFactory), InitializingBean.afterPropertiesSet(), DisposableBean.destroy(), BeanPostProcessor.postProcessBeforeInitialization(java.lang.Object, java.lang.String), BeanPostProcessor.postProcessAfterInitialization(java.lang.Object, java.lang.String), AbstractBeanDefinition.getInitMethodName(), AbstractBeanDefinition.getDestroyMethodName(), ApplicationContextAware.setApplicationContext(org.springframework.context.ApplicationContext)

Method Summary
 boolean containsBean(java.lang.String name)
          Does this bean factory contain a bean definition with the given name?
 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, which may be 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, which may be shared or independent, of the given bean name. This method allows a Spring bean factory to be used as a replacement for the Singleton or Prototype design pattern.

Callers may retain references to returned objects in the case of Singleton beans.

This method delegates to the parent factory if the bean cannot be found in this factory instance.

Parameters:
name - name of the bean to return
Returns:
the instance of the bean
Throws:
NoSuchBeanDefinitionException - if there is no bean definition with the specified name
BeansException - if the bean could not be obtained

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. Behaves the same as getBean(String), but provides a measure of type safety by throwing a Spring BeansException if the bean is not of the required type. This means that ClassCastException can't be thrown on casting the result correctly, as can happen with getBean(String).

Parameters:
name - name of the bean to return
requiredType - type the bean must 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:
an instance of the bean
Throws:
BeanNotOfRequiredTypeException - if the bean is not of the required type
NoSuchBeanDefinitionException - if there's no such bean definition
BeansException - if the bean could not be created

containsBean

public boolean containsBean(java.lang.String name)
Does this bean factory contain a bean definition with the given name?

Will ask the parent factory if the bean cannot be found in this factory instance.

Parameters:
name - name of the bean to query
Returns:
whether a bean with the given name is defined

isSingleton

public boolean isSingleton(java.lang.String name)
                    throws NoSuchBeanDefinitionException
Is this bean a singleton? That is, will getBean() always return the same object?

Will ask the parent factory if the bean cannot be found in this factory instance.

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)
                              throws NoSuchBeanDefinitionException
Return the aliases for the given bean name, if defined.

Will ask the parent factory if the bean cannot be found in this factory instance.

Parameters:
name - the bean name to check for aliases
Returns:
the aliases, or an empty array if none
Throws:
NoSuchBeanDefinitionException - if there's no such bean definition


Copyright (C) 2003-2004 The Spring Framework Project.