2. Core 核心
IoC Container, Events, Resources, i18n, Validation, Data Binding, Type Conversion, SpEL, AOP.
IoC（控制反转）容器，事件，资源，i18n，验证，数据绑定，类型转换，表达式，面向切面编程
2.1 IoC(Inversion of Control) Container
It is a process whereby objects define their dependencies (that is, the other objects they work with) only through constructor arguments, arguments to a factory method, or properties that are set on the object instance after it is constructed or returned from a factory method. The container then injects those dependencies when it creates the bean. This process is fundamentally the inverse (hence the name, Inversion of Control) of the bean itself controlling the instantiation or location of its dependencies by using direct construction of classes or a mechanism such as the Service Locator pattern.
项目的依赖（对象）仅通过构造器参数，工厂方法参数或者通过构造器或工厂方法返回的实例对象的set方法来定义他们的依赖（属性）。容器在bean对象创建时，将依赖注入到bean对象中。这个过程通过使用类的直接构造或服务定位模式机制，从根本上反转了bean本身控制实例化或依赖的位置
org.springframework.beans和 org.springframework.context是SpringIoC容器的基础
BeanFactory接口提供了能够管理任何类型对象的高级配置机制。
ApplicationContext时BeanFactory的一个子接口，他包含了：
更容易与AOP特性集成 Easier integration with Spring’s AOP features
消息资源处理 Message resource handling
事件发布 Event publication
特定于应用程序的Context（例如WebApplicationContext应用在web应用中） Application-layer specific contexts such as the WebApplicationContext for use in web applications.
In short, the BeanFactory provides the configuration framework and basic functionality, and the ApplicationContext adds more enterprise-specific functionality. The ApplicationContext is a complete superset of the BeanFactory and is used exclusively in this chapter in descriptions of Spring’s IoC container.
所以说，BeanFactory提供了配置框架和基础功能，ApplicationContext增加了更多特定功能。ApplicationContext时BeanFactory的一个完整超集，它在本章描述Spring的IoC容器时专用。
In Spring, the objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. Otherwise, a bean is simply one of many objects in your application. Beans, and the dependencies among them, are reflected in the configuration metadata used by a container.
在Spring中，构成应用程序主干并由Spring IoC容器管理的对象称为bean。bean是由Spring IoC容器实例化、组装和管理的对象。另外，bean只是应用程序中的众多对象之一。bean及其之间的依赖关系反映在容器使用的配置元数据中。
2.1.1 补充
Service Locator Pattern：服务定位模式，一种设计模式。当我们希望使用JNDI查找来定位各种服务时，选择此种设计模式。这种设计模式使用了缓存技术。
第一次需要服务时，服务定位器在JNDI中查找并缓存服务对象。
再次查找相同的服务时，将在缓存中完成，提高了程序的性能
JNDI
2.2 Container OverView 容器综述
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.
ApplicationContext这个接口就代表IoC容器，它负责实例化、配置和组装bean。容器通过读取配置文件的元数据来获取要实例化、配置和组装哪些对象的指令。配置文件支持xml,Java注解和纯Java代码。它允许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。
这个描述就是说对象的实例化，分配和管理由容器来负责，你只需要将这些信息用xml配置文件或注解或Java代码配置即可
Several implementations of the ApplicationContext interface are supplied with Spring. In stand-alone applications, it is common to create an instance of ClassPathXmlApplicationContext or FileSystemXmlApplicationContext. While XML has been the traditional format for defining configuration metadata, you can instruct the container to use Java annotations or code as the metadata format by providing a small amount of XML configuration to declaratively enable support for these additional metadata formats
ApplicationContext的几个实现由Spring提供，通常你需要创建 ClassPathXmlApplicationContext或FileSystemXmlApplicationContext的实例。你也可以通过配置使用Java注解结合少量的XML配置来指示容器使用Java注释或代码作为元数据格式。
In most application scenarios, explicit user code is not required to instantiate one or more instances of a Spring IoC container. For example, in a web application scenario, a simple eight (or so) lines of boilerplate web descriptor XML in the web.xml file of the application typically suffices (see Convenient ApplicationContext Instantiation for Web Applications). If you use the Spring Tools for Eclipse (an Eclipse-powered development environment), you can easily create this boilerplate configuration with a few mouse clicks or keystrokes.
就是说，大多数情况下你不需要显示的代码来实例化一个容器，只需要少量的配置就足够了
The following diagram shows a high-level view of how Spring works. Your application classes are combined with configuration metadata so that, after the ApplicationContext is created and initialized, you have a fully configured and executable system or application.
2.2.1 Configuration Metadata
基于注解的配置：spring2.5+
基于Java的配置：spring3.0+
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.
你可以在xml配置文件中使用标签或在带有@Configuration注解的java类中使用@Bean来定义Bean
Typically, one does not configure fine-grained domain objects in the container, because it is usually the responsibility of DAOs and business logic to create and load domain objects.
通常，不会在容器中配置细粒度域对象，因为通常由DAOs和业务逻辑负责创建和加载域对象，这时可以使用Spring与AspectJ的集成来配置在IoC容器控制之外创建的对象。
基于xml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>
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The id attribute is a string that identifies the individual bean definition. 用来标识单个bean
The class attribute defines the type of the bean and uses the fully qualified classname. 这个bean对应类的全限定名
2.2.2 实例化容器
ApplicationContext context = new ClassPathXmlApplicationContext("services.xml", "daos.xml");
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2.2.3 组合xml配置元数据 Composing XML-based Configuration Metadata
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文件可能很有用。通常，每个单独的XML配置文件表示体系结构中的逻辑层或模块。
<beans>
<import resource="services.xml"/>
<import resource="resources/messageSource.xml"/>
<import resource="/resources/themeSource.xml"/>
<bean id="bean1" class="..."/>
<bean id="bean2" class="..."/>
</beans>
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It is possible, but not recommended, to reference files in parent directories using a relative “…/” path. Doing so creates a dependency on a file that is outside the current application. In particular, this reference is not recommended for classpath: URLs (for example, classpath:../services.xml), where the runtime resolution process chooses the “nearest” classpath root and then looks into its parent directory. Classpath configuration changes may lead to the choice of a different, incorrect directory.You can always use fully qualified resource locations instead of relative paths: for example, file:C:/config/services.xml or classpath:/config/services.xml. However, be aware that you are coupling your application’s configuration to specific absolute locations. It is generally preferable to keep an indirection for such absolute locations — for example, through “${…}” placeholders that are resolved against JVM system properties at runtime.
此处提示最好不要使用相对路径，你可以使用绝对路径(不建议)，和classpath，但是不要将配置文件耦合在系统的绝对路径，因为换了操作系统（在服务器部署）时很可能出问题。
2.2.4 Using the Container 容器的使用
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 requiredType), you can retrieve instances of your beans.
The ApplicationContext lets you read bean definitions and access them, as the following example shows:
通过ApplicationContext接口的getBean方法获取Bean对象的实例。
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();
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