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Spring @Bean and @Configuration

發布時間：2025/3/17 javascript 21 豆豆

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四、學習spring 注解的使用

4.12?Java-based container configuration

4.12.1?Basic concepts: @Bean and @Configuration

The central artifacts in Spring’s new Java-configuration support are?@Configuration-annotated classes and?@Bean -annotated methods.

The?@Bean ?annotation is used to indicate that a method instantiates, configures and initializes a new object to be managed by the Spring IoC container. For those familiar with Spring's?<beans/>?XML configuration the?@Bean?annotation plays the same role as the?<bean/>?element. You can use?@Bean?annotated methods with any Spring?@Component, however, they are most often used with?@Configuration?beans.

Annotating a class with?@Configuration??indicates that its primary purpose is as a source of bean definitions. Furthermore,?@Configuration?classes allow inter-bean dependencies to be defined by simply calling other?@Bean?methods in the same class. The simplest possible?@Configuration?class would read as follows:

@Configuration
public class AppConfig { ?
? ?@Bean
? ?public MyService myService() { ? ? ? ?
? ? ? ? ?return new MyServiceImpl();
? ?}

}

The?AppConfig?class above would be equivalent to the following Spring?<beans/>?XML:

The?@Bean?and?@Configuration?annotations will be discussed in depth in the sections below. First, however, we'll cover the various ways of creating a spring container using Java-based configuration.

4.12.2 AnnotationConfigApplicationContext

The sections below document Spring’s?AnnotationConfigApplicationContext, new in Spring 3.0. This versatile?ApplicationContext?implementation is capable of accepting not only?@Configuration?classes as input, but also plain?@Component?classes and classes annotated with JSR-330 metadata.

When?@Configuration?classes are provided as input, the?@Configuration?class itself is registered as a bean definition, and all declared?@Bean?methods within the class are also registered as bean definitions.

When?@Component?and JSR-330 classes are provided, they are registered as bean definitions, and it is assumed that DI metadata such as?@Autowired?or?@Inject?are used within those classes where necessary.

Simple construction

In much the same way that Spring XML files are used as input when instantiating a?ClassPathXmlApplicationContext,?@Configuration?classes may be used as input when instantiating an?AnnotationConfigApplicationContext. This allows for completely XML-free usage of the Spring container:

public static void main(String[] args) {
? ?ApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);//如上所定義的AppConfig class 文件
? ?MyService myService = ctx.getBean(MyService.class);
? ?myService.doStuff();
}

As mentioned above,?AnnotationConfigApplicationContext?is not limited to working only with?@Configuration?classes. Any?@Component?or JSR-330 annotated class may be supplied as input to the constructor. For example:

public static void main(String[] args) {
? ?ApplicationContext ctx = new AnnotationConfigApplicationContext(MyServiceImpl.class, Dependency1.class, Dependency2.class);
? ?MyService myService = ctx.getBean(MyService.class);
? ?myService.doStuff();
}

The above assumes that?MyServiceImpl,?Dependency1?and?Dependency2?use Spring dependency injection annotations such as?@Autowired.

Building the container programmatically using register(Class<?>…)

An?AnnotationConfigApplicationContext?may be instantiated using a no-arg constructor and then configured using the?register()?method. This approach is particularly useful when programmatically building an?AnnotationConfigApplicationContext.

public?static?void?main(String[]?args)?{AnnotationConfigApplicationContext?ctx?=?new?AnnotationConfigApplicationContext();ctx.register(AppConfig.class,?OtherConfig.class);ctx.register(AdditionalConfig.class);ctx.refresh();MyService?myService?=?ctx.getBean(MyService.class);myService.doStuff(); }

Support for web applications with AnnotationConfigWebApplicationContext

A?WebApplicationContext?variant of?AnnotationConfigApplicationContext?is available with?AnnotationConfigWebApplicationContext. This implementation may be used when configuring the Spring?ContextLoaderListener?servlet listener, Spring MVC?DispatcherServlet, etc. What follows is a?web.xml?snippet that configures a typical Spring MVC web application. Note the use of the?contextClass?context-param and init-param:

<web-app><context-param><param-name>contextClass</param-name><param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext????????</param-value></context-param><context-param><param-name>contextConfigLocation</param-name><param-value>com.acme.AppConfig</param-value></context-param><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener><servlet><servlet-name>dispatcher</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextClass</param-name><param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext????????????</param-value></init-param><init-param><param-name>contextConfigLocation</param-name><param-value>com.acme.web.MvcConfig</param-value></init-param></servlet><servlet-mapping><servlet-name>dispatcher</servlet-name><url-pattern>/app/*</url-pattern></servlet-mapping></web-app>

轉載于:https://my.oschina.net/u/2308739/blog/419631

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