spring的自动扫描机制,注解使用ComponentScan

@ComponentScan(basePackages = {"context.cache"})

其内部使用ClassPathBeanDefinitionScanner来实现,
ClassPathBeanDefinitionScanner会扫描包名下面带@Service注解相关的类,然后转解析为BeanDefinition,最后完成自动扫描注册

ClassPathBeanDefinitionScanner构建函数需要传入一个BeanDefinitionRegistry实例对象

测试代码:

public class ClassPathBeanDefinitionScannerTests {

    private static final String BASE_PACKAGE = "example.scannable";


    @Test
    public void testSimpleScanWithDefaultFiltersAndPostProcessors() {
        GenericApplicationContext context = new GenericApplicationContext();
        ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(context);
        int beanCount = scanner.scan(BASE_PACKAGE);
        assertEquals(13, beanCount);
        assertTrue(context.containsBean("serviceInvocationCounter"));
        assertTrue(context.containsBean("fooServiceImpl"));
        assertTrue(context.containsBean("stubFooDao"));
        assertTrue(context.containsBean("myNamedComponent"));
        assertTrue(context.containsBean("myNamedDao"));
        assertTrue(context.containsBean("thoreau"));
        assertTrue(context.containsBean(AnnotationConfigUtils.CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
        assertTrue(context.containsBean(AnnotationConfigUtils.AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
        assertTrue(context.containsBean(AnnotationConfigUtils.REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
        assertTrue(context.containsBean(AnnotationConfigUtils.COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
        assertTrue(context.containsBean(AnnotationConfigUtils.EVENT_LISTENER_PROCESSOR_BEAN_NAME));
        assertTrue(context.containsBean(AnnotationConfigUtils.EVENT_LISTENER_FACTORY_BEAN_NAME));
        context.refresh();

        FooServiceImpl fooService = context.getBean("fooServiceImpl", FooServiceImpl.class);
        assertTrue(context.getDefaultListableBeanFactory().containsSingleton("myNamedComponent"));
        assertEquals("bar", fooService.foo(123));
        assertEquals("bar", fooService.lookupFoo(123));
        assertTrue(context.isPrototype("thoreau"));
    }
}