# 1.4.3. 使用depends-on

如果一个 bean 是另一个 bean 的依赖项，那通常意味着一个 bean 被设置为另一个 bean 的属性。通常，您使用基于 XML 的配置元数据中的[`<ref/>` 元素来完成此操作。](https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-ref-element)但是，有时 bean 之间的依赖关系不那么直接。例如，当需要触发类中的静态初始化程序时，例如用于数据库驱动程序注册。在初始化使用此元素的 bean 之前，`depends-on`属性可以显式强制初始化一个或多个 bean。以下示例使用`depends-on`属性来表达对单个 bean 的依赖：

```xml
<bean id="beanOne" class="ExampleBean" depends-on="manager"/>
<bean id="manager" class="ManagerBean" />
```

要表达对多个 bean 的依赖关系，请提供 bean 名称列表作为`depends-on`属性值（逗号、空格和分号是有效的分隔符）：

```xml
<bean id="beanOne" class="ExampleBean" depends-on="manager,accountDao">
    <property name="manager" ref="manager" />
</bean>

<bean id="manager" class="ManagerBean" />
<bean id="accountDao" class="x.y.jdbc.JdbcAccountDao" />
```

> `depends-on`属性既可以指定初始化时间依赖项，也可以指定对应的销毁时间依赖项（仅在[单例bean 的情况下）。](https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-factory-scopes-singleton)定义与给定 bean 的关系的从属`depends-on` bean首先被销毁，然后给定 bean 本身被销毁。这样，`depends-on`也可以控制关机顺序。


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