spring源码分析之<context:component-scan/>vs<annotation-config/>

1.<context:annotation-config/>

xsd中说明：

<xsd:element name="annotation-config">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Activates various annotations to be detected in bean classes: Spring's @Required and @Autowired, as well as JSR 250's @PostConstruct, @PreDestroy and @Resource (if available), JAX-WS's @WebServiceRef (if available), EJB3's @EJB (if available), and JPA's @PersistenceContext and @PersistenceUnit (if available). Alternatively, you may choose to activate the individual BeanPostProcessors for those annotations. Note: This tag does not activate processing of Spring's @Transactional or EJB3's @TransactionAttribute annotation. Consider the use of the <tx:annotation-driven> tag for that purpose.
]]>
</xsd:documentation>
</xsd:annotation>
</xsd:element>

解析发生在在解析xml文件中，解析类为：AnnotationConfigBeanDefinitionParser.java

public BeanDefinition parse(Element element, ParserContext parserContext) {
        Object source = parserContext.extractSource(element);

        // Obtain bean definitions for all relevant BeanPostProcessors.
        Set<BeanDefinitionHolder> processorDefinitions =
                AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);

        // Register component for the surrounding <context:annotation-config> element.
        CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
        parserContext.pushContainingComponent(compDefinition);

        // Nest the concrete beans in the surrounding component.
        for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
            parserContext.registerComponent(new BeanComponentDefinition(processorDefinition));
        }

        // Finally register the composite component.
        parserContext.popAndRegisterContainingComponent();

        return null;
    }

2.<context:component-scan/>

<xsd:element name="component-scan">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Scans the classpath for annotated components that will be auto-registered as Spring beans. By default, the Spring-provided @Component, @Repository, @Service, and @Controller stereotypes will be detected. Note: This tag implies the effects of the 'annotation-config' tag, activating @Required, @Autowired, @PostConstruct, @PreDestroy, @Resource, @PersistenceContext and @PersistenceUnit annotations in the component classes, which is usually desired for autodetected components (without external configuration). Turn off the 'annotation-config' attribute to deactivate this default behavior, for example in order to use custom BeanPostProcessor definitions for handling those annotations. Note: You may use placeholders in package paths, but only resolved against system properties (analogous to resource paths). A component scan results in new bean definition being registered; Spring's PropertyPlaceholderConfigurer will apply to those bean definitions just like to regular bean definitions, but it won't apply to the component scan settings themselves.
]]>
</xsd:documentation>
</xsd:annotation>
<xsd:complexType>
<xsd:sequence>
<xsd:element name="include-filter" type="filterType" minOccurs="0" maxOccurs="unbounded">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Controls which eligible types to include for component scanning.
]]>
</xsd:documentation>
</xsd:annotation>
</xsd:element>
<xsd:element name="exclude-filter" type="filterType" minOccurs="0" maxOccurs="unbounded">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Controls which eligible types to exclude for component scanning.
]]>
</xsd:documentation>
</xsd:annotation>
</xsd:element>
</xsd:sequence>
<xsd:attribute name="base-package" type="xsd:string" use="required">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
The comma-separated list of packages to scan for annotated components.
]]>
</xsd:documentation>
</xsd:annotation>
</xsd:attribute>
<xsd:attribute name="resource-pattern" type="xsd:string">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Controls the class files eligible for component detection. Defaults to "**/*.class", the recommended value.
]]>
</xsd:documentation>
</xsd:annotation>
</xsd:attribute>
<xsd:attribute name="use-default-filters" type="xsd:boolean" default="true">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Indicates whether automatic detection of classes annotated with @Component, @Repository, @Service, or @Controller should be enabled. Default is "true".
]]>
</xsd:documentation>
</xsd:annotation>
</xsd:attribute>
<xsd:attribute name="annotation-config" type="xsd:boolean" default="true">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Indicates whether the implicit annotation post-processors should be enabled. Default is "true".
]]>
</xsd:documentation>
</xsd:annotation>
</xsd:attribute>
<xsd:attribute name="name-generator" type="xsd:string">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
The fully-qualified class name of the BeanNameGenerator to be used for naming detected components.
]]>
</xsd:documentation>
<xsd:appinfo>
<tool:annotation>
<tool:expected-type type="java.lang.Class"/>
<tool:assignable-to type="org.springframework.beans.factory.support.BeanNameGenerator"/>
</tool:annotation>
</xsd:appinfo>
</xsd:annotation>
</xsd:attribute>
<xsd:attribute name="scope-resolver" type="xsd:string">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
The fully-qualified class name of the ScopeMetadataResolver to be used for resolving the scope of detected components.
]]>
</xsd:documentation>
<xsd:appinfo>
<tool:annotation>
<tool:expected-type type="java.lang.Class"/>
<tool:assignable-to type="org.springframework.context.annotation.ScopeMetadataResolver"/>
</tool:annotation>
</xsd:appinfo>
</xsd:annotation>
</xsd:attribute>
<xsd:attribute name="scoped-proxy">
<xsd:annotation>
<xsd:documentation>
<![CDATA[
Indicates whether proxies should be generated for detected components, which may be necessary when using scopes in a proxy-style fashion. Default is to generate no such proxies.
]]>
</xsd:documentation>
</xsd:annotation>
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:enumeration value="no"/>
<xsd:enumeration value="interfaces"/>
<xsd:enumeration value="targetClass"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:complexType>
</xsd:element>

注意：红色的一行中，说明<context:component-scan>包含<context:annotation-config>，且<context:annotation-config>的作用是：

Indicates whether automatic detection of classes annotated with @Component, @Repository, @Service, or @Controller should be enabled.

而<context:component-scan>解析发生在在解析xml文件中，解析类为：ComponentScanBeanDefinitionParser.java

    public BeanDefinition parse(Element element, ParserContext parserContext) {
        String[] basePackages = StringUtils.tokenizeToStringArray(element.getAttribute(BASE_PACKAGE_ATTRIBUTE),
                ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);

        // Actually scan for bean definitions and register them.
        ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
        Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
        registerComponents(parserContext.getReaderContext(), beanDefinitions, element);

        return null;
    }

注册过程如下：

protected void registerComponents(
            XmlReaderContext readerContext, Set<BeanDefinitionHolder> beanDefinitions, Element element) {

        Object source = readerContext.extractSource(element);
        CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), source);

        for (BeanDefinitionHolder beanDefHolder : beanDefinitions) {
            compositeDef.addNestedComponent(new BeanComponentDefinition(beanDefHolder));
        }

        // Register annotation config processors, if necessary.
        boolean annotationConfig = true;
        if (element.hasAttribute(ANNOTATION_CONFIG_ATTRIBUTE)) {
            annotationConfig = Boolean.valueOf(element.getAttribute(ANNOTATION_CONFIG_ATTRIBUTE));
        }
        if (annotationConfig) {
            Set<BeanDefinitionHolder> processorDefinitions =
                    AnnotationConfigUtils.registerAnnotationConfigProcessors(readerContext.getRegistry(), source);
            for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
                compositeDef.addNestedComponent(new BeanComponentDefinition(processorDefinition));
            }
        }

        readerContext.fireComponentRegistered(compositeDef);
    }

其中，红色部分是关于<annotation-config>部分的。