3.Dubbo源码分析----Dubbo的Service注解分析

 前面已经对Dubbo跟Spring Boot的结合原理的分析了[https://www.jianshu.com/p/7048774803d5](Dubbo源码分析----Dubbo在Spring Boot启动时如何运行的),现在就是对前面几个注册的Bean进行分析
 ServiceAnnotationBeanPostProcessor这个类用来处理Service标签的类。前面对于这个类有简单的介绍,这个类实现了spring的BeanDefinitionRegistryPostProcessor类,在Spring中这个类的是可以用来拓展的,当用户需要自定义注册bean的时候可以是实现这个接口的postProcessBeanDefinitionRegistry方法。这个接口的方法可以在BeanFactoryPostProcessor检测开始之前注册其他bean定义。查看ServiceAnnotationBeanPostProcessor的postProcessBeanDefinitionRegistry方法

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        //packagesToScan(需要扫描的包参数)在创建这个Bean的时候当作参数传入了,这里会对参数进行去空格,并把配置文件中的配置的扫描参数也放到一起处理
        Set resolvedPackagesToScan = resolvePackagesToScan(packagesToScan);
        //判断扫描列表是不是空
        if (!CollectionUtils.isEmpty(resolvedPackagesToScan)) {
            //注册包里面的Bean
            registerServiceBeans(resolvedPackagesToScan, registry);
        } else {
            if (logger.isWarnEnabled()) {
                logger.warn("packagesToScan is empty , ServiceBean registry will be ignored!");
            }
        }
    }

 主要的逻辑集中在registerServiceBeans方法中,这个方法就是查找需要扫面包里面的类贴有Service标签的类并注册成Bean。

    private void registerServiceBeans(Set packagesToScan, BeanDefinitionRegistry registry) {
        // 定义扫描对象,该类继承了ClassPathBeanDefinitionScanner类,继承的原因主要是将ClassPathBeanDefinitionScanner中的protect类型的方法变成public级别的
        //ClassPathBeanDefinitionScanner的作用就是扫面类路径中的Bean候选者
        DubboClassPathBeanDefinitionScanner scanner =
                new DubboClassPathBeanDefinitionScanner(registry, environment, resourceLoader);
        //获取beanNameGenerator(用于为bean定义生成bean名称的策略接口)
        BeanNameGenerator beanNameGenerator = resolveBeanNameGenerator(registry);
        //设置BeanNameGenerator以用于检测到的scanner,这里可以理解为为注册的Bean生成BeanName用
        scanner.setBeanNameGenerator(beanNameGenerator);
        //将包含类型过滤器添加到包含列表的,就是一个过滤器,用来过滤贴了Service注解的对象。
        scanner.addIncludeFilter(new AnnotationTypeFilter(Service.class));
        //遍历包
        for (String packageToScan : packagesToScan) {
            // Registers @Service Bean first
            //注册指定包路径下的贴有Service的Bean
            scanner.scan(packageToScan);
            //查找@Service的所有BeanDefinitionHolders,无论@ComponentScan是否扫描。
            Set beanDefinitionHolders =
                    findServiceBeanDefinitionHolders(scanner, packageToScan, registry, beanNameGenerator);
            //如果BeanDefinitionHolder不为空,对于BeanDefinitionHolder这个对象不知道可以去看看前面的文章
            if (!CollectionUtils.isEmpty(beanDefinitionHolders)) {
                //遍历然后注册Bean
                for (BeanDefinitionHolder beanDefinitionHolder : beanDefinitionHolders) {
                    registerServiceBean(beanDefinitionHolder, registry, scanner);
                }
                if (logger.isInfoEnabled()) {
                    logger.info(beanDefinitionHolders.size() + " annotated Dubbo's @Service Components { " +
                            beanDefinitionHolders +
                            " } were scanned under package[" + packageToScan + "]");
                }
            } else {
                if (logger.isWarnEnabled()) {
                    logger.warn("No Spring Bean annotating Dubbo's @Service was found under package["
                            + packageToScan + "]");
                }
            }
        }
    }

上面的逻辑比较简单,就是对传入的包路径进行扫描,找到贴有@service标签的类,并会把生成的Bean相关信息封装到BeanDefinitionHolder中,然后对BeanDefinitionHolder集合进行遍历,进行自定义的注册,接下来就是分析自定义注册的部分registerServiceBean方法。

    private void registerServiceBean(BeanDefinitionHolder beanDefinitionHolder, BeanDefinitionRegistry registry,
                                     DubboClassPathBeanDefinitionScanner scanner) {
        //获取beanDefinitionHolder中的BeanClass
        Class beanClass = resolveClass(beanDefinitionHolder);
        //beanClass中的Service注解
        Service service = findAnnotation(beanClass, Service.class);
        //从service注解中获取用户定义的interfaceClass如果没有定义则用beanClass的接口类中的第一个
        Class interfaceClass = resolveServiceInterfaceClass(beanClass, service);
        //获取BeanName
        String annotatedServiceBeanName = beanDefinitionHolder.getBeanName();
        //使用BeanDefinitionBuilder创建Bean,bean的类型是ServiceBean,这里面会添加一些信息到Bean中比如ref,provider,monitor等信息
        AbstractBeanDefinition serviceBeanDefinition =
                buildServiceBeanDefinition(service, interfaceClass, annotatedServiceBeanName);
        // 生成beanName
        String beanName = generateServiceBeanName(service, interfaceClass, annotatedServiceBeanName);
        //检查是否已经创建了相同名称跟类型的bean,没有就进行注册
        if (scanner.checkCandidate(beanName, serviceBeanDefinition)) {
            //注册Bean,这里可以参考前面的spring的源码分析
            registry.registerBeanDefinition(beanName, serviceBeanDefinition);
            if (logger.isInfoEnabled()) {
                logger.info("The BeanDefinition[" + serviceBeanDefinition +
                        "] of ServiceBean has been registered with name : " + beanName);
            }
        } else {
            if (logger.isWarnEnabled()) {
                logger.warn("The Duplicated BeanDefinition[" + serviceBeanDefinition +
                        "] of ServiceBean[ bean name : " + beanName +
                        "] was be found , Did @DubboComponentScan scan to same package in many times?");
            }
        }
    }
//------------创建Bean 的buildServiceBeanDefinition方法
    private AbstractBeanDefinition buildServiceBeanDefinition(Service service, Class interfaceClass,
                                                              String annotatedServiceBeanName) {
        //注册Bean 的Class为ServiceBean.class
        BeanDefinitionBuilder builder = rootBeanDefinition(ServiceBean.class);
        //获取AbstractBeanDefinition,是为了后面添加属性
        AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();
        //从AbstractBeanDefinition中获取MutablePropertyValues对象(允许对属性进行简单操作,并提供构造函数以支持Map中的深层复制和构造)
        MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
        String[] ignoreAttributeNames = of("provider", "monitor", "application", "module", "registry", "protocol",
                "interface", "interfaceName");
        //添加自己的属性适配器
        propertyValues.addPropertyValues(new AnnotationPropertyValuesAdapter(service, environment, ignoreAttributeNames));
        //将“ref”属性引用到带注释的@Service Bean
        // References "ref" property to annotated-@Service Bean
        addPropertyReference(builder, "ref", annotatedServiceBeanName);
        // Set interface
        builder.addPropertyValue("interface", interfaceClass.getName());
        //设置标签中配置的providerName到provider属性,后面基本都是这种操作
        String providerConfigBeanName = service.provider();
        if (StringUtils.hasText(providerConfigBeanName)) {
            addPropertyReference(builder, "provider", providerConfigBeanName);
        }
        ........
}

 这样上面的Service标签的处理就已经结束了,注意上面最后创建的Bean的是ServiceBean,这个类很重要。接下来就是对Reference标签的处理分析。

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