3.4.4 Lazy-initialized beans 延迟初始化bean

By default, ApplicationContext implementations eagerly create and configure all singleton beans as part of the initialization process. Generally, this pre-instantiation is desirable, because errors in the configuration or surrounding environment are discovered immediately, as opposed to hours or even days later. When this behavior is not desirable, you can prevent pre-instantiation of a singleton bean by marking the bean definition as lazy-initialized. A lazy-initialized bean tells the IoC container to create a bean instance when it is first requested, rather than at startup.

In XML, this behavior is controlled by the lazy-init attribute on the `` element; for example:

默认情况下，ApplicationContext实现急切地创建和配置所有singleton bean作为初始化过程的一部分。 通常，这种预实例化是期望的，因为配置或周围环境中的错误被立即发现，而不是数小时或甚至数天之后。 当这种行为不是所期望的，你可以通过将bean定义标记为延迟初始化来阻止单例bean的预实例化。 一个延迟初始化的bean告诉IoC容器在第一次请求时而不是在启动时创建一个bean实例。

在XML中，此行为由<bean/>元素上的lazy-init属性控制; 例如：

<bean id="lazy" class="com.foo.ExpensiveToCreateBean" lazy-init="true"/>
<bean name="not.lazy" class="com.foo.AnotherBean"/>

When the preceding configuration is consumed by an ApplicationContext, the bean named lazy is not eagerly pre-instantiated when the ApplicationContext is starting up, whereas the not.lazy bean is eagerly pre-instantiated.

However, when a lazy-initialized bean is a dependency of a singleton bean that is not lazy-initialized, the ApplicationContext creates the lazy-initialized bean at startup, because it must satisfy the singleton’s dependencies. The lazy-initialized bean is injected into a singleton bean elsewhere that is not lazy-initialized.

You can also control lazy-initialization at the container level by using the default-lazy-init attribute on the <beans/> element; for example:

当前面的配置被一个ApplicationContext消费时，名为lazy的bean在ApplicationContext启动时不会被预先实例化，而not.lazybean被预先实例化。

但是，当一个延迟初始化的bean是单例bean的依赖，而这个单例bean又不是 lazy初始化时，ApplicationContext在启动时创建延迟初始化的bean，因为它必须满足singleton的依赖。因此延迟加载的bean会被注入单例bean。

您还可以通过使用<bean />元素上的default-lazy-init属性在容器级别控制延迟初始化; 例如：

<beans default-lazy-init="true">
    <!-- no beans will be pre-instantiated... -->
</beans>

results matching ""

    No results matching ""