Spring源码解析-IOC容器的实现-ApplicationContext

　　上面我们已经知道了IOC的建立的基本步骤了，我们就可以用编码的方式和IOC容器进行建立过程了。其实Spring已经为我们提供了很多实现，想必上面的简单扩展，如XMLBeanFacroty等。我们一般是用ApplicationContext这个接口，这个接口实现了基本的功能外，还添加了很多相应的功能，根据看下面的源码我来看看是怎么实现更多的功能的。

public interface ApplicationContext extends ListableBeanFactory, HierarchicalBeanFactory,
        MessageSource, ApplicationEventPublisher, ResourcePatternResolver {

    /**
     * 返回一个唯一的bean的ID
     */
    String getId();

    /**
     * 返回一个name为context
    */
    String getDisplayName();

    /**
     * 返回第一次加载的时间戳
     */
    long getStartupDate();

    /**
     * Return the parent context, or <code>null</code> if there is no parent
     * and this is the root of the context hierarchy.
     * @return the parent context, or <code>null</code> if there is no parent
     */
    ApplicationContext getParent();

    /**
     * Expose AutowireCapableBeanFactory functionality for this context.
     * <p>This is not typically used by application code, except for the purpose
     * of initializing bean instances that live outside the application context,
     * applying the Spring bean lifecycle (fully or partly) to them.
     * <p>Alternatively, the internal BeanFactory exposed by the
     * {@link ConfigurableApplicationContext} interface offers access to the
     * AutowireCapableBeanFactory interface too. The present method mainly
     * serves as convenient, specific facility on the ApplicationContext
     * interface itself.
     * @return the AutowireCapableBeanFactory for this context
     * @throws IllegalStateException if the context does not support
     * the AutowireCapableBeanFactory interface or does not hold an autowire-capable
     * bean factory yet (usually if <code>refresh()</code> has never been called)
     * @see ConfigurableApplicationContext#refresh()
     * @see ConfigurableApplicationContext#getBeanFactory()
     */
    AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException;

}
以上是ApplicationContext的源码，她继承了相应的接口，ListableBeanFactory, HierarchicalBeanFactory,
        MessageSource, ApplicationEventPublisher, ResourcePatternResolver去进行相应的扩展。因此ApplicationContext增加了相应的很多功能。

如下：1.支持不同的信息源，因为他扩展了MessageSource接口，这个就支持了消息的国际化实现。2.支持相应的事件。因为继承了ApplicationEventPublisher，这样就为上下文提供了事件的机制。3.访问资源。这个体现在ResourceLoader和Resource的支持上，这样我们就可以在不同的地方得到bean定义的资源。

因此在我们使用的时候，一般都使用ApplicationContext作为IOC容器的基本形式。创建IOC容器。

ListableBeanFactory源码：

public interface ListableBeanFactory extends BeanFactory {

    /**
     * 检查beaFactory是否包含bean的定义  通过bean的name
     * <p>Does not consider any hierarchy this factory may participate in,
     * and ignores any singleton beans that have been registered by
     * other means than bean definitions.
     * @param beanName the name of the bean to look for
     * @return if this bean factory contains a bean definition with the given name
     * @see #containsBean
     */
    boolean containsBeanDefinition(String beanName);

    /**
     * 返回在BeanFactory中存在的bean的定义的数量
     * <p>Does not consider any hierarchy this factory may participate in,
     * and ignores any singleton beans that have been registered by
     * other means than bean definitions.
     * @return the number of beans defined in the factory
     */
    int getBeanDefinitionCount();

    /**
     * 返回所有关于bean定义的name
     * <p>Does not consider any hierarchy this factory may participate in,
     * and ignores any singleton beans that have been registered by
     * other means than bean definitions.
     * @return the names of all beans defined in this factory,
     * or an empty array if none defined
     */
    String[] getBeanDefinitionNames();
    
    /**
     * 返回bean的名称  通过bean定义的类型
     * judging from either bean definitions or the value of <code>getObjectType</code>
     * in the case of FactoryBeans.
     * <p><b>NOTE: This method introspects top-level beans only.</b> It does <i>not</i>
     * check nested beans which might match the specified type as well.
     * <p>Does consider objects created by FactoryBeans, which means that FactoryBeans
     * will get initialized. If the object created by the FactoryBean doesn't match,
     * the raw FactoryBean itself will be matched against the type.
     * <p>Does not consider any hierarchy this factory may participate in.
     * Use BeanFactoryUtils' <code>beanNamesForTypeIncludingAncestors</code>
     * to include beans in ancestor factories too.
     * <p>Note: Does <i>not</i> ignore singleton beans that have been registered
     * by other means than bean definitions.
     * <p>This version of <code>getBeanNamesForType</code> matches all kinds of beans,
     * be it singletons, prototypes, or FactoryBeans. In most implementations, the
     * result will be the same as for <code>getBeanNamesOfType(type, true, true)</code>.
     * <p>Bean names returned by this method should always return bean names <i>in the
     * order of definition</i> in the backend configuration, as far as possible.
     * @param type the class or interface to match, or <code>null</code> for all bean names
     * @return the names of beans (or objects created by FactoryBeans) matching
     * the given object type (including subclasses), or an empty array if none
     * @see FactoryBean#getObjectType
     * @see BeanFactoryUtils#beanNamesForTypeIncludingAncestors(ListableBeanFactory, Class)
     */
    String[] getBeanNamesForType(Class type);

    /**
     * 返回bean的名称  通过bean定义的类型 (including subclasses),
     * judging from either bean definitions or the value of <code>getObjectType</code>
     * in the case of FactoryBeans.
     * <p><b>NOTE: This method introspects top-level beans only.</b> It does <i>not</i>
     * check nested beans which might match the specified type as well.
     * <p>Does consider objects created by FactoryBeans if the "allowEagerInit" flag is set,
     * which means that FactoryBeans will get initialized. If the object created by the
     * FactoryBean doesn't match, the raw FactoryBean itself will be matched against the
     * type. If "allowEagerInit" is not set, only raw FactoryBeans will be checked
     * (which doesn't require initialization of each FactoryBean).
$     * <p>Does not consider any hierarchy this factory may participate in.
     * Use BeanFactoryUtils' <code>beanNamesForTypeIncludingAncestors</code>
     * to include beans in ancestor factories too.
     * <p>Note: Does <i>not</i> ignore singleton beans that have been registered
     * by other means than bean definitions.
     * <p>Bean names returned by this method should always return bean names <i>in the
     * order of definition</i> in the backend configuration, as far as possible.
     * @param type the class or interface to match, or <code>null</code> for all bean names
     * @param includeNonSingletons whether to include prototype or scoped beans too
     * or just singletons (also applies to FactoryBeans)
     * @param allowEagerInit whether to initialize <i>lazy-init singletons</i> and
     * <i>objects created by FactoryBeans</i> (or by factory methods with a
     * "factory-bean" reference) for the type check. Note that FactoryBeans need to be
     * eagerly initialized to determine their type: So be aware that passing in "true"
     * for this flag will initialize FactoryBeans and "factory-bean" references.
     * @return the names of beans (or objects created by FactoryBeans) matching
     * the given object type (including subclasses), or an empty array if none
     * @see FactoryBean#getObjectType
     * @see BeanFactoryUtils#beanNamesForTypeIncludingAncestors(ListableBeanFactory, Class, boolean, boolean)
     */
    String[] getBeanNamesForType(Class type, boolean includeNonSingletons, boolean allowEagerInit);

    /**
     * 通过对象类型返回相应bean的实例 (including
     * subclasses), judging from either bean definitions or the value of
     * <code>getObjectType</code> in the case of FactoryBeans.
     * <p><b>NOTE: This method introspects top-level beans only.</b> It does <i>not</i>
     * check nested beans which might match the specified type as well.
     * <p>Does consider objects created by FactoryBeans, which means that FactoryBeans
     * will get initialized. If the object created by the FactoryBean doesn't match,
     * the raw FactoryBean itself will be matched against the type.
     * <p>Does not consider any hierarchy this factory may participate in.
     * Use BeanFactoryUtils' <code>beansOfTypeIncludingAncestors</code>
     * to include beans in ancestor factories too.
     * <p>Note: Does <i>not</i> ignore singleton beans that have been registered
     * by other means than bean definitions.
     * <p>This version of getBeansOfType matches all kinds of beans, be it
     * singletons, prototypes, or FactoryBeans. In most implementations, the
     * result will be the same as for <code>getBeansOfType(type, true, true)</code>.
     * <p>The Map returned by this method should always return bean names and
     * corresponding bean instances <i>in the order of definition</i> in the
     * backend configuration, as far as possible.
     * @param type the class or interface to match, or <code>null</code> for all concrete beans
     * @return a Map with the matching beans, containing the bean names as
     * keys and the corresponding bean instances as values
     * @throws BeansException if a bean could not be created
     * @since 1.1.2
     * @see FactoryBean#getObjectType
     * @see BeanFactoryUtils#beansOfTypeIncludingAncestors(ListableBeanFactory, Class)
     */
    <T> Map<String, T> getBeansOfType(Class<T> type) throws BeansException;

    /**
     * 通过对象类型返回相应bean的实例 (including
     * subclasses), judging from either bean definitions or the value of
     * <code>getObjectType</code> in the case of FactoryBeans.
     * <p><b>NOTE: This method introspects top-level beans only.</b> It does <i>not</i>
     * check nested beans which might match the specified type as well.
     * <p>Does consider objects created by FactoryBeans if the "allowEagerInit" flag is set,
     * which means that FactoryBeans will get initialized. If the object created by the
     * FactoryBean doesn't match, the raw FactoryBean itself will be matched against the
     * type. If "allowEagerInit" is not set, only raw FactoryBeans will be checked
     * (which doesn't require initialization of each FactoryBean).
     * <p>Does not consider any hierarchy this factory may participate in.
     * Use BeanFactoryUtils' <code>beansOfTypeIncludingAncestors</code>
     * to include beans in ancestor factories too.
     * <p>Note: Does <i>not</i> ignore singleton beans that have been registered
     * by other means than bean definitions.
     * <p>The Map returned by this method should always return bean names and
     * corresponding bean instances <i>in the order of definition</i> in the
     * backend configuration, as far as possible.
     * @param type the class or interface to match, or <code>null</code> for all concrete beans
     * @param includeNonSingletons whether to include prototype or scoped beans too
     * or just singletons (also applies to FactoryBeans)
     * @param allowEagerInit whether to initialize <i>lazy-init singletons</i> and
     * <i>objects created by FactoryBeans</i> (or by factory methods with a
     * "factory-bean" reference) for the type check. Note that FactoryBeans need to be
     * eagerly initialized to determine their type: So be aware that passing in "true"
     * for this flag will initialize FactoryBeans and "factory-bean" references.
     * @return a Map with the matching beans, containing the bean names as
     * keys and the corresponding bean instances as values
     * @throws BeansException if a bean could not be created
     * @see FactoryBean#getObjectType
     * @see BeanFactoryUtils#beansOfTypeIncludingAncestors(ListableBeanFactory, Class, boolean, boolean)
     */
    <T> Map<String, T> getBeansOfType(Class<T> type, boolean includeNonSingletons, boolean allowEagerInit)
            throws BeansException;

    /*
     * 查找所有的bean  通过注解

　　*Find all beans whose <code>Class</code> has the supplied {@link java.lang.annotation.Annotation} type.
     * @param annotationType the type of annotation to look for
     * @return a Map with the matching beans, containing the bean names as
     * keys and the corresponding bean instances as values
     * @throws BeansException if a bean could not be created
     */
    Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType)
            throws BeansException;

    /**
     * Find a {@link Annotation} of <code>annotationType</code> on the specified
     * bean, traversing its interfaces and super classes if no annotation can be
     * found on the given class itself.
     * @param beanName the name of the bean to look for annotations on
     * @param annotationType the annotation class to look for
     * @return the annotation of the given type found, or <code>null</code>
     */
    <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType);

}
HierarchicalBeanFactory源码：

public interface HierarchicalBeanFactory extends BeanFactory {
    
    /**
     * 返回父 bean factory, or <code>null</code> if there is none.
     */
    BeanFactory getParentBeanFactory();

    /**
     * 返回本地是否存在bean的名称为name的bean
     * ignoring beans defined in ancestor contexts.
     * <p>This is an alternative to <code>containsBean</code>, ignoring a bean
     * of the given name from an ancestor bean factory.
     * @param name the name of the bean to query
     * @return whether a bean with the given name is defined in the local factory
     * @see org.springframework.beans.factory.BeanFactory#containsBean
     */
    boolean containsLocalBean(String name);

}

MessageSource的源码：

public interface MessageSource {

    /**
     * Try to resolve the message. Return default message if no message was found.
     * @param code the code to lookup up, such as 'calculator.noRateSet'. Users of
     * this class are encouraged to base message names on the relevant fully
     * qualified class name, thus avoiding conflict and ensuring maximum clarity.
     * @param args array of arguments that will be filled in for params within
     * the message (params look like "{0}", "{1,date}", "{2,time}" within a message),
     * or <code>null</code> if none.
     * @param defaultMessage String to return if the lookup fails
     * @param locale the Locale in which to do the lookup
     * @return the resolved message if the lookup was successful;
     * otherwise the default message passed as a parameter
     * @see java.text.MessageFormat
     */
    String getMessage(String code, Object[] args, String defaultMessage, Locale locale);

    /**
     * Try to resolve the message. Treat as an error if the message can't be found.
     * @param code the code to lookup up, such as 'calculator.noRateSet'
     * @param args Array of arguments that will be filled in for params within
     * the message (params look like "{0}", "{1,date}", "{2,time}" within a message),
     * or <code>null</code> if none.
     * @param locale the Locale in which to do the lookup
     * @return the resolved message
     * @throws NoSuchMessageException if the message wasn't found
     * @see java.text.MessageFormat
     */
    String getMessage(String code, Object[] args, Locale locale) throws NoSuchMessageException;

    /**
     * Try to resolve the message using all the attributes contained within the
     * <code>MessageSourceResolvable</code> argument that was passed in.
     * <p>NOTE: We must throw a <code>NoSuchMessageException</code> on this method
     * since at the time of calling this method we aren't able to determine if the
     * <code>defaultMessage</code> property of the resolvable is null or not.
     * @param resolvable value object storing attributes required to properly resolve a message
     * @param locale the Locale in which to do the lookup
     * @return the resolved message
     * @throws NoSuchMessageException if the message wasn't found
     * @see java.text.MessageFormat
     */
    String getMessage(MessageSourceResolvable resolvable, Locale locale) throws NoSuchMessageException;

}

ApplicationEventPublisher的源码：

public interface ApplicationEventPublisher {

    /**
     * Notify all listeners registered with this application of an application
     * event. Events may be framework events (such as RequestHandledEvent)
     * or application-specific events.
     * @param event the event to publish
     * @see org.springframework.web.context.support.RequestHandledEvent
     */
    void publishEvent(ApplicationEvent event);

}

ResourcePatternResolver的源码：

public interface ResourcePatternResolver extends ResourceLoader {

    /**
     * Pseudo URL prefix for all matching resources from the class path: "classpath*:"
     * This differs from ResourceLoader's classpath URL prefix in that it
     * retrieves all matching resources for a given name (e.g. "/beans.xml"),
     * for example in the root of all deployed JAR files.
     * @see org.springframework.core.io.ResourceLoader#CLASSPATH_URL_PREFIX
     */
    String CLASSPATH_ALL_URL_PREFIX = "classpath*:";

    /**
     * Resolve the given location pattern into Resource objects.
     * <p>Overlapping resource entries that point to the same physical
     * resource should be avoided, as far as possible. The result should
     * have set semantics.
     * @param locationPattern the location pattern to resolve
     * @return the corresponding Resource objects
     * @throws IOException in case of I/O errors
     */
    Resource[] getResources(String locationPattern) throws IOException;

}

这个接口继承了ResourceLoader，所以让ApplicationContext也支持ResourceLoader和Resource.ResourceLoader里面有一个方法是得到Resource,可以看看：

public interface ResourceLoader {

    /** Pseudo URL prefix for loading from the class path: "classpath:" */
    String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;


    /**
     * 通过资源的地址得到Resource
     */
    Resource getResource(String location);

    /**
     * Expose the ClassLoader used by this ResourceLoader.
     * <p>Clients which need to access the ClassLoader directly can do so
     * in a uniform manner with the ResourceLoader, rather than relying
     * on the thread context ClassLoader.
     * @return the ClassLoader (never <code>null</code>)
     */
    ClassLoader getClassLoader();

}