beanfactory.java

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/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory;

import org.springframework.beans.BeansException;

/**
 * The root interface for accessing a Spring bean container.
 * This is the basic client view of a bean container;
 * further interfaces such as {@link ListableBeanFactory} and
 * {@link org.springframework.beans.factory.config.ConfigurableBeanFactory}
 * are available for specific purposes.
 *
 * <p>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.
 *
 * <p>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.
 *
 * <p>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 this BeanFactory interface and its subinterfaces.
 *
 * <p>Normally a BeanFactory will load bean definitions stored in a configuration
 * source (such as an XML document), and use the <code>org.springframework.beans</code>
 * 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 (Dependency Injection).
 *
 * <p>In contrast to the methods in {@link ListableBeanFactory}, all of the
 * operations in this interface will also check parent factories if this is a
 * {@link HierarchicalBeanFactory}. If a bean is not found in this factory instance,
 * the immediate parent factory will be asked. Beans in this factory instance
 * are supposed to override beans of the same name in any parent factory.
 *
 * <p>Bean factory implementations should support the standard bean lifecycle interfaces
 * as far as possible. The full set of initialization methods and their standard order is:<br>
 * 1. BeanNameAware's <code>setBeanName</code><br>
 * 2. BeanFactoryAware's <code>setBeanFactory</code><br>
 * 3. ResourceLoaderAware's <code>setResourceLoader</code>
 * (only applicable when running in an application context)<br>
 * 4. ApplicationEventPublisherAware's <code>setApplicationEventPublisher</code>
 * (only applicable when running in an application context)<br>
 * 5. MessageSourceAware's <code>setMessageSource</code>
 * (only applicable when running in an application context)<br>
 * 6. ApplicationContextAware's <code>setApplicationContext</code>
 * (only applicable when running in an application context)<br>
 * 7. ServletContextAware's <code>setServletContext</code>
 * (only applicable when running in a web application context)<br>
 * 8. <code>postProcessBeforeInitialization</code> methods of BeanPostProcessors<br>
 * 9. InitializingBean's <code>afterPropertiesSet</code><br>
 * 10. a custom init-method definition<br>
 * 11. <code>postProcessAfterInitialization</code> methods of BeanPostProcessors
 *
 * <p>On shutdown of a bean factory, the following lifecycle methods apply:<br>
 * 1. DisposableBean's <code>destroy</code><br>
 * 2. a custom destroy-method definition
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 13 April 2001
 * @see BeanNameAware#setBeanName
 * @see BeanFactoryAware#setBeanFactory
 * @see org.springframework.context.ResourceLoaderAware#setResourceLoader
 * @see org.springframework.context.ApplicationEventPublisherAware#setApplicationEventPublisher
 * @see org.springframework.context.MessageSourceAware#setMessageSource
 * @see org.springframework.context.ApplicationContextAware#setApplicationContext
 * @see org.springframework.web.context.ServletContextAware#setServletContext
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization
 * @see InitializingBean#afterPropertiesSet
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization
 * @see DisposableBean#destroy
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getDestroyMethodName
 */
public interface BeanFactory {

	/**
	 * Used to dereference a {@link FactoryBean} instance and distinguish it from
	 * beans <i>created</i> by the FactoryBean. For example, if the bean named
	 * <code>myJndiObject</code> is a FactoryBean, getting <code>&myJndiObject</code>
	 * will return the factory, not the instance returned by the factory.
	 */
	String FACTORY_BEAN_PREFIX = "&";


	/**
	 * Return an instance, which may be shared or independent, of the specified bean.
	 * <p>This method allows a Spring BeanFactory 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.
	 * <p>Translates aliases back to the corresponding canonical bean name.
	 * Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the name of the bean to retrieve
	 * @return an instance of the bean
	 * @throws NoSuchBeanDefinitionException if there is no bean definition
	 * with the specified name
	 * @throws BeansException if the bean could not be obtained
	 */
	Object getBean(String name) throws BeansException;

	/**
	 * Return an instance, which may be shared or independent, of the specified bean.
	 * <p>Behaves the same as {@link #getBean(String)}, but provides a measure of type
	 * safety by throwing a BeanNotOfRequiredTypeException 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 {@link #getBean(String)}.
	 * <p>Translates aliases back to the corresponding canonical bean name.
	 * Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the name of the bean to retrieve
	 * @param requiredType type the bean must match. Can be an interface or superclass
	 * of the actual class, or <code>null</code> for any match. For example, if the value
	 * is <code>Object.class</code>, this method will succeed whatever the class of the
	 * returned instance.
	 * @return an instance of the bean
	 * @throws BeanNotOfRequiredTypeException if the bean is not of the required type
	 * @throws NoSuchBeanDefinitionException if there's no such bean definition
	 * @throws BeansException if the bean could not be created
	 */
	Object getBean(String name, Class requiredType) throws BeansException;

	/**
	 * Does this bean factory contain a bean with the given name?
	 * <p>Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the name of the bean to query
	 * @return whether a bean with the given name is defined
	 */
	boolean containsBean(String name);

	/**
	 * Is this bean a shared singleton? That is, will {@link #getBean} always
	 * return the same instance?
	 * <p>Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the name of the bean to query
	 * @return whether this bean corresponds to a singleton instance
	 * @throws NoSuchBeanDefinitionException if there is no bean with the given name
	 * @see #getBean
	 */
	boolean isSingleton(String name) throws NoSuchBeanDefinitionException;

	/**
	 * Determine the type of the bean with the given name. More specifically,
	 * check the type of object that {@link #getBean} would return.
	 * For a FactoryBean, return the type of object that the FactoryBean creates.
	 * @param name the name of the bean to query
	 * @return the type of the bean, or <code>null</code> if not determinable
	 * @throws NoSuchBeanDefinitionException if there is no bean with the given name
	 * @since 1.1.2
	 * @see #getBean
	 * @see FactoryBean#getObjectType()
	 */
	Class getType(String name) throws NoSuchBeanDefinitionException;

	/**
	 * Return the aliases for the given bean name, if defined.
	 * <p>Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the bean name to check for aliases
	 * @return the aliases, or an empty array if none
	 * @throws NoSuchBeanDefinitionException if there is no bean definition
	 * with the specified name
	 */
	String[] getAliases(String name) throws NoSuchBeanDefinitionException;

}