The IoC Container 1.10.5-1.10.9

1.10.5. Defining Bean Metadata within Components

@Component
public class FactoryMethodComponent {

    private static int i;

    @Bean
    @Qualifier("public")
    public TestBean publicInstance() {
        return new TestBean("publicInstance");
    }

    // use of a custom qualifier and autowiring of method parameters
    @Bean
    protected TestBean protectedInstance(
            @Qualifier("public") TestBean spouse,
            @Value("#{privateInstance.age}") String country) {
        TestBean tb = new TestBean("protectedInstance", 1);
        tb.setSpouse(spouse);
        tb.setCountry(country);
        return tb;
    }

    @Bean
    private TestBean privateInstance() {
        return new TestBean("privateInstance", i++);
    }

    @Bean
    @RequestScope
    public TestBean requestScopedInstance() {
        return new TestBean("requestScopedInstance", 3);
    }
}

上述代码向Spring Container中注册了TestBean的bean定义，可以使用@Qualifier和@RequestScope约束bean的功能，同时还在工厂方法protectedInstance中通过传参的方式支持自动装配其他的bean，并且通过@Qualifier和@Value注解约束了其功能，"#{privateInstance.age}"代表privateInstance单例对象中的age字段作为参数进行装配。

A Spring Expression Language element defines the value of the property through the notation #{ <expression> }

@Bean注解在@Component中和@Configuration中注解的方法的调用方式是不同的。@Component注解的类不会通过CGLIB进行代理，而@Configuration注解的类会通过CGLIB进行代理。

1.10.6. Naming Autodetected Components

@Component, @Repository, @Service, and @Controller支持指定bean name。示例如下：

@Service("myMovieLister")
public class SimpleMovieLister {
    // ...
}

@Repository
public class MovieFinderImpl implements MovieFinder {
    // ...
}

默认的bean name命名是驼峰式命名，由类名生成。Spring支持篡改它自身的命名规则，通过如下方式：

@Configuration
@ComponentScan(basePackages = "org.example", nameGenerator = MyNameGenerator.class)
public class AppConfig {
    ...
}

MyNameGenerator继承自BeanNameGenerator接口。
xml定义方式如下：

<beans>
    <context:component-scan base-package="org.example"
        name-generator="org.example.MyNameGenerator" />
</beans>

一般情况下，使用Spring默认命名规则已经足够。

1.10.7. Providing a Scope for Autodetected Components

Scope使用：

@Scope("prototype")
@Repository
public class MovieFinderImpl implements MovieFinder {
    // ...
}

注意事项：

@Scope annotations are only introspected on the concrete bean class (for annotated components) or the factory method (for @Bean methods)

Sping支持自定义scope解析器：

@Configuration
@ComponentScan(basePackages = "org.example", scopeResolver = MyScopeResolver.class)
public class AppConfig {
    ...
}

<beans>
    <context:component-scan base-package="org.example" scope-resolver="org.example.MyScopeResolver"/>
</beans>

支持配置bean的代理模式，全局配置：

@Configuration
@ComponentScan(basePackages = "org.example", scopedProxy = ScopedProxyMode.INTERFACES)
public class AppConfig {
    ...
}

<beans>
    <context:component-scan base-package="org.example" scoped-proxy="interfaces"/>
</beans>

1.10.8. Providing Qualifier Metadata with Annotations

针对候选人配置@Qualifier注解：

@Component
@Qualifier("Action")
public class ActionMovieCatalog implements MovieCatalog {
    // ...
}

@Component
@Genre("Action")
public class ActionMovieCatalog implements MovieCatalog {
    // ...
}

@Component
@Offline
public class CachingMovieCatalog implements MovieCatalog {
    // ...
}

1.10.9. Generating an Index of Candidate Components

基于注解的配置需要扫描classpath来查找相应的bean定义等信息，可以通过是生成Index of Candidate Components提前生成相关信息，从而避免扫描，加快Spring应用的启动速度。

具体方法是引入如下包：

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-indexer</artifactId>
        <version>5.1.5.RELEASE</version>
        <optional>true</optional>
    </dependency>
</dependencies>

编译过后会生成META-INF/spring.components：

#
#Sun Feb 24 22:17:27 CST 2019
examples.FactoryMethodComponent=org.springframework.stereotype.Component
examples.ComponentExample=org.springframework.stereotype.Component
examples.SessionScopedUserService=org.springframework.stereotype.Component
examples.AppConfig=org.springframework.stereotype.Component
examples.SimpleMovieLister=org.springframework.stereotype.Component
examples.SessionScopedService=org.springframework.stereotype.Component
examples.JpaMovieFinder=org.springframework.stereotype.Component