• 2.2.1 配置元数据
• 2.2.2 实例化一个容器
  • 编写基于 XML 的配置元数据
• 2.2.3 使用容器

The org.springframework.context.ApplicationContext interface represents the Spring IoC container and is responsible for instantiating, configuring, and assembling the beans. The container gets its instructions on what objects to instantiate, configure, and assemble by reading configuration metadata. The configuration metadata is represented in XML, Java annotations, or Java code. It lets you express the objects that compose your application and the rich interdependencies between those objects.

org.springframework.context.ApplicationContext接口代表 Spring IoC 容器，负责实例化、配置和组装 bean。容器通过读取配置元数据来获取有关要实例化、配置和组装哪些对象的指令。配置元数据以 XML、Java 注释或 Java 代码表示。它可以让您表达组成应用程序的对象以及这些对象之间丰富的相互依赖关系。

2.2.1 配置元数据

Configuration Metadata

the Spring IoC container consumes a form of configuration metadata. This configuration metadata represents how you, as an application developer, tell the Spring container to instantiate, configure, and assemble the objects in your application.

Spring IoC 容器使用一种形式的配置元数据。此配置元数据表示您作为应用程序开发人员如何告诉 Spring 容器实例化、配置和组装应用程序中的对象。

在 Spring 容器中配置元数据的方式

• XML-based configuration

• Annotation-based configuration

  Spring 2.5 引入了对基于注解的配置元数据的支持。

• Java-based configuration
  从 Spring 3.0 开始，Spring JavaConfig 项目提供的许多特性成为核心 Spring Framework 的一部分。因此，您可以使用 Java 而不是 XML 文件来定义应用程序类外部的 bean

Spring configuration consists of at least one and typically more than one bean definition that the container must manage. XML-based configuration metadata configures these beans as elements inside a top-level element. Java configuration typically uses @Bean-annotated methods within a @Configuration class.

Spring配置由容器必须管理的至少一个(通常是多个)bean定义组成。基于xml的配置元数据将这些bean配置为顶层元素中的元素。Java配置通常在@Configuration类中使用@ bean注释的方法。

基于xml的配置元数据的基本结构:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="..." class="...">  
        <!-- collaborators and configuration for this bean go here -->
    </bean>

    <bean id="..." class="...">
        <!-- collaborators and configuration for this bean go here -->
    </bean>

    <!-- more bean definitions go here -->

</beans>

• The id attribute is a string that identifies the individual bean definition.
• The class attribute defines the type of the bean and uses the fully qualified
  classname.

2.2.2 实例化一个容器

The location path or paths supplied to an ApplicationContext constructor are resource strings that let the container load configuration metadata from a variety of external resources, such as the local file system, the Java CLASSPATH, and so on.

提供给ApplicationContext构造函数的一个或多个位置路径是资源字符串，允许容器从各种外部资源（例如本地文件系统、Java CLASSPATH等）加载配置元数据

ApplicationContext context = new ClassPathXmlApplicationContext("services.xml", "daos.xml");

service.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- services -->

    <bean id="petStore" class="org.springframework.samples.jpetstore.services.PetStoreServiceImpl">
        <property name="accountDao" ref="accountDao"/>
        <property name="itemDao" ref="itemDao"/>
        <!-- additional collaborators and configuration for this bean go here -->
    </bean>

    <!-- more bean definitions for services go here -->

</beans>

daos.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="accountDao"
        class="org.springframework.samples.jpetstore.dao.jpa.JpaAccountDao">
        <!-- additional collaborators and configuration for this bean go here -->
    </bean>

    <bean id="itemDao" class="org.springframework.samples.jpetstore.dao.jpa.JpaItemDao">
        <!-- additional collaborators and configuration for this bean go here -->
    </bean>

    <!-- more bean definitions for data access objects go here -->

</beans>

编写基于 XML 的配置元数据

It can be useful to have bean definitions span multiple XML files. Often, each individual XML configuration file represents a logical layer or module in your architecture.

让 bean 定义跨越多个 XML 文件会很有用。通常，每个单独的 XML 配置文件都代表您架构中的一个逻辑层或模块。

You can use the application context constructor to load bean definitions from all these XML fragments. This constructor takes multiple Resource locations. Alternatively, use one or more occurrences of the element to load bean definitions from another file or files.

您可以使用应用程序上下文构造函数从所有这些 XML 片段加载 bean 定义。该构造函数采用多个Resource位置。或者，使用一个或多个元素从另一个文件或多个文件加载 bean 定义。

<beans>
    <import resource="services.xml"/>
    <import resource="resources/messageSource.xml"/>
    <import resource="/resources/themeSource.xml"/>

    <bean id="bean1" class="..."/>
    <bean id="bean2" class="..."/>
</beans>

外部豆定义是从三个文件加载： services.xml，messageSource.xml，和themeSource.xml。所有位置路径都相对于执行导入的定义文件，因此services.xml必须与执行导入的文件位于同一目录或类路径位置，messageSource.xml并且themeSource.xml必须位于resources导入文件位置下方的位置。如您所见，前导斜杠被忽略。但是，鉴于这些路径是相对的，最好根本不使用斜杠。<beans/>根据 Spring Schema，被导入文件的内容，包括顶级元素，必须是有效的 XML bean 定义。

2.2.3 使用容器

Using the Container

The ApplicationContext is the interface for an advanced factory capable of maintaining a registry of different beans and their dependencies. By using the method T getBean(String name, Class<T> requiredType), you can retrieve instances of your beans.

ApplicationContext是一个高级工厂的接口，能够维护不同 bean 及其依赖项的注册表。通过使用 方法 T getBean(String name, Class<T> requiredType)，您可以检索 bean 的实例。

The ApplicationContext lets you read bean definitions and access them,

ApplicationContext让你读bean定义和访问它们

// create and configure beans
ApplicationContext context = new ClassPathXmlApplicationContext("services.xml", "daos.xml");

// retrieve configured instance
PetStoreService service = context.getBean("petStore", PetStoreService.class);

// use configured instance
List<String> userList = service.getUsernameList();