Spring Bean的作用域（转）

Spring Bean的作用域

.singleton  [单例] eg：<bean id="personService" class="com.yinger.service.impl.PersonServiceBean" scope="singleton"></bean>

在每个Spring IoC容器中一个bean定义只有一个对象实例。

请注意Spring的singleton bean概念与“四人帮”（GoF）模式一书中定义的Singleton模式是完全不同的。

经典的GoF Singleton模式中所谓的对象范围是指在每一个ClassLoader中指定class创建的实例有且仅有一个。

把Spring的singleton作用域描述成一个container对应一个bean实例最为贴切。亦即，假如在单个Spring容器内定义了某个指定class的bean，

那么Spring容器将会创建一个且仅有一个由该bean定义指定的类实例。

org.springframework.beans.factory.config.ConfigurableBeanFactory

/**
 * Configuration interface to be implemented by most bean factories. Provides
 * facilities to configure a bean factory, in addition to the bean factory
 * client methods in the {@link org.springframework.beans.factory.BeanFactory}
 * interface.
 *
 * <p>This bean factory interface is not meant to be used in normal application
 * code: Stick to {@link org.springframework.beans.factory.BeanFactory} or
 * {@link org.springframework.beans.factory.ListableBeanFactory} for typical
 * needs. This extended interface is just meant to allow for framework-internal
 * plug'n'play and for special access to bean factory configuration methods.
 *
 * @author Juergen Hoeller
 * @since 03.11.2003
 * @see org.springframework.beans.factory.BeanFactory
 * @see org.springframework.beans.factory.ListableBeanFactory
 * @see ConfigurableListableBeanFactory
 */
public interface ConfigurableBeanFactory extends HierarchicalBeanFactory, SingletonBeanRegistry {

    /**
     * Scope identifier for the standard singleton scope: "singleton".
     * Custom scopes can be added via {@code registerScope}.
     * @see #registerScope
     */
    String SCOPE_SINGLETON = "singleton";

    /**
     * Scope identifier for the standard prototype scope: "prototype".
     * Custom scopes can be added via {@code registerScope}.
     * @see #registerScope
     */
    String SCOPE_PROTOTYPE = "prototype";

默认情况下会在容器启动时初始化bean，但我们可以指定Bean节点的lazy-init=“true”来延迟初始化bean，这时候，只有第一次获取bean会才初始化bean。

如：<bean id="xxx" class="cn.itcast.OrderServiceBean" lazy-init="true"/>

如果想对所有bean都应用延迟初始化，可以在根节点beans设置default-lazy-init=“true“，如下：

<beans default-lazy-init="true“ ...>

.prototype [原型]

每次从容器获取bean都是新的对象。

对于prototype作用域的bean，有一点非常重要，那就是Spring不能对一个prototype bean的整个生命周期负责：容器在初始化、配置、装饰或者是

装配完一个prototype实例后，将它交给客户端，随后就对该prototype实例不闻不问了。不管何种作用域，容器都会调用所有对象的初始化生命周期回调方法。

但对prototype而言，任何配置好的析构生命周期回调方法都将不会被调用。清除prototype作用域的对象并释放任何prototype bean所持有的昂贵资源，

都是客户端代码的职责。（让Spring容器释放被prototype作用域bean占用资源的一种可行方式是，通过使用bean的后置处理器，该处理器持有要被清除的bean的引用。）

以下的三种scope只是在web应用中才可以使用

.request

.session

.global session

使用这三种配置之前要先初始化Web配置

http://www.cnblogs.com/njtcy/p/3328076.html

/**
 * When used as a type-level annotation in conjunction with
 * {@link org.springframework.stereotype.Component @Component},
 * {@code @Scope} indicates the name of a scope to use for instances of
 * the annotated type.
 *
 * <p>When used as a method-level annotation in conjunction with
 * {@link Bean @Bean}, {@code @Scope} indicates the name of a scope to use
 * for the instance returned from the method.
 *
 * <p><b>NOTE:</b> {@code @Scope} annotations are only introspected on the
 * concrete bean class (for annotated components) or the factory method
 * (for {@code @Bean} methods). In contrast to XML bean definitions,
 * there is no notion of bean definition inheritance, and inheritance
 * hierarchies at the class level are irrelevant for metadata purposes.
 *
 * <p>In this context, <em>scope</em> means the lifecycle of an instance,
 * such as {@code singleton}, {@code prototype}, and so forth. Scopes
 * provided out of the box in Spring may be referred to using the
 * {@code SCOPE_*} constants available in the {@link ConfigurableBeanFactory}
 * and {@code WebApplicationContext} interfaces.
 *
 * <p>To register additional custom scopes, see
 * {@link org.springframework.beans.factory.config.CustomScopeConfigurer
 * CustomScopeConfigurer}.
 *
 * @author Mark Fisher
 * @author Chris Beams
 * @author Sam Brannen
 * @since 2.5
 * @see org.springframework.stereotype.Component
 * @see org.springframework.context.annotation.Bean
 */
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Scope {

    /**
     * Alias for {@link #scopeName}.
     * @see #scopeName
     */
    @AliasFor("scopeName")
    String value() default "";

    /**
     * Specifies the name of the scope to use for the annotated component/bean.
     * <p>Defaults to an empty string ({@code ""}) which implies
     * {@link ConfigurableBeanFactory#SCOPE_SINGLETON SCOPE_SINGLETON}.
     * @since 4.2
     * @see ConfigurableBeanFactory#SCOPE_PROTOTYPE
     * @see ConfigurableBeanFactory#SCOPE_SINGLETON
     * @see org.springframework.web.context.WebApplicationContext#SCOPE_REQUEST
     * @see org.springframework.web.context.WebApplicationContext#SCOPE_SESSION
     * @see #value
     */
    @AliasFor("value")
    String scopeName() default "";

    /**
     * Specifies whether a component should be configured as a scoped proxy
     * and if so, whether the proxy should be interface-based or subclass-based.
     * <p>Defaults to {@link ScopedProxyMode#DEFAULT}, which typically indicates
     * that no scoped proxy should be created unless a different default
     * has been configured at the component-scan instruction level.
     * <p>Analogous to {@code <aop:scoped-proxy/>} support in Spring XML.
     * @see ScopedProxyMode
     */
    ScopedProxyMode proxyMode() default ScopedProxyMode.DEFAULT;

}