Talk about dubbo’s SpringExtensionFactory

sequence

This article focuses on dubbo’s 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);

}
Copy the code

• The ExtensionFactory interface defines the getExtension method

SpringExtensionFactory

Dubbo – 2.7.3 / dubbo – config/dubbo – config – spring/SRC/main/Java/org/apache/dubbo/config/spring/extension/SpringExtensionFacto ry.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(); }}}}Copy the code

• SpringExtensionFactory implements the ExtensionFactory method, which provides the addApplicationContext static method to add the ApplicationContext, Also registered SHUTDOWN_HOOK_LISTENER; The getExtension method first gets the bean from ApplicationContext based on name, then gets the bean from ApplicationContext based on Type, or returns NULL

SpringExtensionFactoryTest

Dubbo – 2.7.3 / dubbo – config/dubbo – config – spring/SRC/test/Java/org/apache/dubbo/config/spring/extension/SpringExtensionFacto ryTest.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() {
        returnnew HelloServiceImpl(); }}Copy the code

• SpringExtensionFactoryTest springExtensionFactory init approach to add context1 and context2; The extension is then verified to be fetched based on SPI, based on name, and based on Type

summary

SpringExtensionFactory implements the ExtensionFactory method, which provides the addApplicationContext static method to add the ApplicationContext, Also registered SHUTDOWN_HOOK_LISTENER; The getExtension method first gets the bean from ApplicationContext based on name, then gets the bean from ApplicationContext based on Type, or returns NULL

doc

• SpringExtensionFactory