序

本文主要研究一下dubbo的SpringExtensionFactory

ExtensionFactory

dubbo-2.7.3/dubbo-common/src/main/java/org/apache/dubbo/common/extension/ExtensionFactory.java

@SPI
public interface ExtensionFactory {

    /**
     * Get extension.
     *
     * @param type object type.
     * @param name object name.
     * @return object instance.
     */
    <T> T getExtension(Class<T> type
 
,String name);

}
複製程式碼

• ExtensionFactory介面定義了getExtension方法

SpringExtensionFactory

dubbo-2.7.3/dubbo-config/dubbo-config-spring/src/main/java/org/apache/dubbo/config/spring/extension/SpringExtensionFactory.java

public class SpringExtensionFactory implements ExtensionFactory {
    private static final Logger logger = LoggerFactory.getLogger(SpringExtensionFactory.class);

    private static final Set<ApplicationContext> CONTEXTS = new ConcurrentHashSet<ApplicationContext>();
    private static final ApplicationListener SHUTDOWN_HOOK_LISTENER = new ShutdownHookListener();

    public static void addApplicationContext(ApplicationContext context) {
        CONTEXTS.add(context);
        if
 
 (context instanceof ConfigurableApplicationContext) {
            ((ConfigurableApplicationContext) context).registerShutdownHook();
            DubboShutdownHook.getDubboShutdownHook().unregister();
        }
        BeanFactoryUtils.addApplicationListener(context,SHUTDOWN_HOOK_LISTENER);
    }

    public static void removeApplicationContext(ApplicationContext context) {
        CONTEXTS.remove(context);
    }

    public static Set<ApplicationContext> getContexts
 
() {
        return CONTEXTS;
    }

    // currently for test purpose
    public static void clearContexts() {
        CONTEXTS.clear();
    }

    @Override
    @SuppressWarnings("unchecked")
    public <T> T getExtension(Class<T> type,String name) {

        //SPI should be get from SpiExtensionFactory
        if (type.isInterface() && type.isAnnotationPresent(SPI.class)) {
            return null;
        }

        for (ApplicationContext context : CONTEXTS) {
            if (context.containsBean(name)) {
                Object bean = context.getBean(name);
                if (type.isInstance(bean)) {
                    return (T) bean;
                }
            }
        }

        logger.warn("No spring extension (bean) named:" + name + ",try to find an extension (bean) of type " + type.getName());

        if (Object.class == type) {
            return null;
        }

        for (ApplicationContext context : CONTEXTS) {
            try {
                return context.getBean(type);
            } catch (NoUniqueBeanDefinitionException multiBeanExe) {
                logger.warn("Find more than 1 spring extensions (beans) of type " + type.getName() + ",will stop auto injection. Please make sure you have specified the concrete parameter type and there's only one extension of that type.");
            } catch (NoSuchBeanDefinitionException noBeanExe) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Error when get spring extension(bean) for type:" + type.getName(),noBeanExe);
                }
            }
        }

        logger.warn("No spring extension (bean) named:" + name + ",type:" + type.getName() + " found,stop get bean.");

        return null;
    }

    private static class ShutdownHookListener implements ApplicationListener {
        @Override
        public void onApplicationEvent(ApplicationEvent event) {
            if (event instanceof ContextClosedEvent) {
                DubboShutdownHook shutdownHook = DubboShutdownHook.getDubboShutdownHook();
                shutdownHook.doDestroy();
            }
        }
    }
}
複製程式碼

• SpringExtensionFactory實現了ExtensionFactory方法，它提供了addApplicationContext靜態方法來新增ApplicationContext，同時註冊了SHUTDOWN_HOOK_LISTENER；其getExtension方法首先根據name從ApplicationContext中獲取bean，獲取不到則在根據type再去ApplicationContext中獲取bean，獲取不到則返回null

SpringExtensionFactoryTest

dubbo-2.7.3/dubbo-config/dubbo-config-spring/src/test/java/org/apache/dubbo/config/spring/extension/SpringExtensionFactoryTest.java

@Configuration
public class SpringExtensionFactoryTest {

    private SpringExtensionFactory springExtensionFactory = new SpringExtensionFactory();
    private AnnotationConfigApplicationContext context1;
    private AnnotationConfigApplicationContext context2;

    @BeforeEach
    public void init() {
        context1 = new AnnotationConfigApplicationContext();
        context1.register(getClass());
        context1.refresh();
        context2 = new AnnotationConfigApplicationContext();
        context2.register(BeanForContext2.class);
        context2.refresh();
        SpringExtensionFactory.addApplicationContext(context1);
        SpringExtensionFactory.addApplicationContext(context2);
    }

    @Test
    public void testGetExtensionBySPI() {
        Protocol protocol = springExtensionFactory.getExtension(Protocol.class,"protocol");
        Assertions.assertNull(protocol);
    }

    @Test
    public void testGetExtensionByName() {
        DemoService bean = springExtensionFactory.getExtension(DemoService.class,"bean1");
        Assertions.assertNotNull(bean);
    }

    @Test
    public void testGetExtensionByTypeMultiple() {
        try {
            springExtensionFactory.getExtension(DemoService.class,"beanname-not-exist");
        } catch (Exception e) {
            e.printStackTrace();
            Assertions.assertTrue(e instanceof NoUniqueBeanDefinitionException);
        }
    }

    @Test
    public void testGetExtensionByType() {
        HelloService bean = springExtensionFactory.getExtension(HelloService.class,"beanname-not-exist");
        Assertions.assertNotNull(bean);
    }

    @AfterEach
    public void destroy() {
        SpringExtensionFactory.clearContexts();
        context1.close();
        context2.close();
    }

    @Bean("bean1")
    public DemoService bean1() {
        return new DemoServiceImpl();
    }

    @Bean("bean2")
    public DemoService bean2() {
        return new DemoServiceImpl();
    }

    @Bean("hello")
    public HelloService helloService() {
        return new HelloServiceImpl();
    }
}
複製程式碼

• SpringExtensionFactoryTest的init方法給springExtensionFactory添加了context1和context2；之後驗證了根據SPI、根據name、根據type來獲取extension

小結

SpringExtensionFactory實現了ExtensionFactory方法，它提供了addApplicationContext靜態方法來新增ApplicationContext，同時註冊了SHUTDOWN_HOOK_LISTENER；其getExtension方法首先根據name從ApplicationContext中獲取bean，獲取不到則在根據type再去ApplicationContext中獲取bean，獲取不到則返回null

doc

• SpringExtensionFactory