Java极客  |  作者  /  铿然一叶 这是Java极客的第 92 篇原创文章

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1. 核心操作

1.初始化GlobalTransactionScanner

2.GlobalTransactionScanner识别启用全局事务的类，添加不同拦截器

3.初始化TM客户端和RM客户端

4.添加destroy钩子

2. 核心类结构

3. 自动装配

通过spring的SPI机制，自动实例化GlobalTransactionScanner。

引入不同的库使用的自动装配类不同，

groupId	artifactId	规范
io.seata	seata-spring-boot-starter	SeataAutoConfiguration
com.alibaba.cloud	spring-cloud-alibaba-seata	GlobalTransactionAutoConfiguration

3.1 seata-spring-boot-starter

3.1.1 入口

SeataAutoConfiguration.java

@ConditionalOnProperty(prefix = SEATA_PREFIX, name = "enabled", havingValue = "true", matchIfMissing = true)
public class SeataAutoConfiguration {
    private static final Logger LOGGER = LoggerFactory.getLogger(SeataAutoConfiguration.class);

    @Bean(BEAN_NAME_FAILURE_HANDLER)
    @ConditionalOnMissingBean(FailureHandler.class)
    public FailureHandler failureHandler() {
        return new DefaultFailureHandlerImpl();
    }

    @Bean
    @DependsOn({BEAN_NAME_SPRING_APPLICATION_CONTEXT_PROVIDER, BEAN_NAME_FAILURE_HANDLER})
    @ConditionalOnMissingBean(GlobalTransactionScanner.class)
    public GlobalTransactionScanner globalTransactionScanner(SeataProperties seataProperties, FailureHandler failureHandler) {
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Automatically configure Seata");
        }
        return new GlobalTransactionScanner(seataProperties.getApplicationId(), seataProperties.getTxServiceGroup(), failureHandler);
    }
}

3.1.2 SPI配置

在seata-spring-boot-starter模块的spring.factories文件中配置了SeataAutoConfiguration类使能自动装配。

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
io.seata.spring.boot.autoconfigure.SeataPropertiesAutoConfiguration,\
io.seata.spring.boot.autoconfigure.SeataDataSourceAutoConfiguration,\
io.seata.spring.boot.autoconfigure.SeataAutoConfiguration,\
io.seata.spring.boot.autoconfigure.HttpAutoConfiguration

3.1.3 SeataProperties参数初始化

GlobalTransactionScanner的构造器参数seataProperties:

GlobalTransactionScanner(seataProperties.getApplicationId(), seataProperties.getTxServiceGroup(), failureHandler);

SeataPropertiesAutoConfiguration.java

AutoConfigureBefore注解配置在SeataAutoConfiguration之前完成初始化。

@ConditionalOnProperty(prefix = SEATA_PREFIX, name = "enabled", havingValue = "true", matchIfMissing = true)
@ComponentScan(basePackages = "io.seata.spring.boot.autoconfigure.properties")
@AutoConfigureBefore({SeataAutoConfiguration.class, SeataDataSourceAutoConfiguration.class})
public class SeataPropertiesAutoConfiguration {
    static {

        PROPERTY_BEAN_MAP.put(SEATA_PREFIX, SeataProperties.class);

3.2 spring-cloud-alibaba-seata

3.2.1 入口

GlobalTransactionAutoConfiguration.java

一步到位把SeataProperties也初始化了，但是少了FailureHandler的初始化：

@Configuration
@EnableConfigurationProperties({SeataProperties.class})
public class GlobalTransactionAutoConfiguration {
    private final ApplicationContext applicationContext;
    private final SeataProperties seataProperties;

    public GlobalTransactionAutoConfiguration(ApplicationContext applicationContext, SeataProperties seataProperties) {
        this.applicationContext = applicationContext;
        this.seataProperties = seataProperties;
    }

    @Bean
    public GlobalTransactionScanner globalTransactionScanner() {
        String applicationName = this.applicationContext.getEnvironment().getProperty("spring.application.name");
        String txServiceGroup = this.seataProperties.getTxServiceGroup();
        if (StringUtils.isEmpty(txServiceGroup)) {
            txServiceGroup = applicationName + "-fescar-service-group";
            this.seataProperties.setTxServiceGroup(txServiceGroup);
        }

        return new GlobalTransactionScanner(applicationName, txServiceGroup);
    }
}

3.2.2 SPI配置

在spring-cloud-alibaba-seata模块的spring.factories文件中配置了GlobalTransactionAutoConfiguration类使能自动装配。

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.alibaba.cloud.seata.rest.SeataRestTemplateAutoConfiguration,\
com.alibaba.cloud.seata.web.SeataHandlerInterceptorConfiguration,\
com.alibaba.cloud.seata.GlobalTransactionAutoConfiguration,\
com.alibaba.cloud.seata.feign.SeataFeignClientAutoConfiguration,\
com.alibaba.cloud.seata.feign.hystrix.SeataHystrixAutoConfiguration

4. 核心类GlobalTransactionScanner

主要作用：

1.实现InitializingBean接口完成bean初始化操作

2.实现ConfigurationChangeListener接口监听seata配置参数变化并做处理

3.实现DisposableBean接口做destroy处理

4.实现ApplicationContextAware接口用户注入ApplicationContext

5.继承AbstractAutoProxyCreator类，重载其方法，添加事务处理拦截器

4.1 初始化操作

1.注册参数变更监听器

2.初始化TM和RM

    @Override
    public void afterPropertiesSet() {
        // 来自service.disableGlobalTransaction配置参数
        if (disableGlobalTransaction) {
            if (LOGGER.isInfoEnabled()) {
                LOGGER.info("Global transaction is disabled.");
            }
            // 添加service.disableGlobalTransaction参数变更监听器，也就是它自己，如果参数变化则会动态初始化TM客户端和RM客户端
            ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                    (ConfigurationChangeListener)this);

            // 如果service.disableGlobalTransaction=false则不会初始化TM客户端和RM客户端
            return;
        }
        // 没有初始化则初始化（TM客户端和RM客户端）
        if (initialized.compareAndSet(false, true)) {
            initClient();
        }
    }

4.2 监听参数变化

监听参数为不启用全局事务变化到启用全局事务，变化后初始化RM和TM。

    @Override
    public void onChangeEvent(ConfigurationChangeEvent event) {
        if (ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION.equals(event.getDataId())) {
            disableGlobalTransaction = Boolean.parseBoolean(event.getNewValue().trim());
            // 监听service.disableGlobalTransaction参数配置，如果启用全局事务并且没有做过初始化则做初始化
            if (!disableGlobalTransaction && initialized.compareAndSet(false, true)) {
                LOGGER.info("{} config changed, old value:{}, new value:{}", ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                        disableGlobalTransaction, event.getNewValue());
                initClient();
            }
        }
    }

4.3 添加拦截器

4.3.1 拦截器实例化

根据条件添加TCC模式和AT模式拦截器：

    @Override
    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        try {
            synchronized (PROXYED_SET) {
                if (PROXYED_SET.contains(beanName)) {
                    return bean;
                }
                interceptor = null;
                //check TCC proxy
                if (TCCBeanParserUtils.isTccAutoProxy(bean, beanName, applicationContext)) {
                    //TCC interceptor, proxy bean of sofa:reference/dubbo:reference, and LocalTCC
                    interceptor = new TccActionInterceptor(TCCBeanParserUtils.getRemotingDesc(beanName));
                    ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                        (ConfigurationChangeListener)interceptor);
                } else {
                    Class<?> serviceInterface = SpringProxyUtils.findTargetClass(bean);
                    Class<?>[] interfacesIfJdk = SpringProxyUtils.findInterfaces(bean);

                    if (!existsAnnotation(new Class[]{serviceInterface})
                        && !existsAnnotation(interfacesIfJdk)) {
                        return bean;
                    }

                    if (globalTransactionalInterceptor == null) {
                        globalTransactionalInterceptor = new GlobalTransactionalInterceptor(failureHandlerHook);
                        // 监听配置参数service.disableGlobalTransaction的变化
                        ConfigurationCache.addConfigListener(
                            ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                            (ConfigurationChangeListener)globalTransactionalInterceptor);
                    }
                    interceptor = globalTransactionalInterceptor;
                }

                LOGGER.info("Bean[{}] with name [{}] would use interceptor [{}]", bean.getClass().getName(), beanName, interceptor.getClass().getName());
                if (!AopUtils.isAopProxy(bean)) {
                    bean = super.wrapIfNecessary(bean, beanName, cacheKey);
                } else {
                    AdvisedSupport advised = SpringProxyUtils.getAdvisedSupport(bean);
                    Advisor[] advisor = buildAdvisors(beanName, getAdvicesAndAdvisorsForBean(null, null, null));
                    for (Advisor avr : advisor) {
                        advised.addAdvisor(0, avr);
                    }
                }
                PROXYED_SET.add(beanName);
                return bean;
            }
        } catch (Exception exx) {
            throw new RuntimeException(exx);
        }
    }

4.3.2 判断事务注解

GlobalTransactional支持类和方法级，GlobalLock仅支持方法级。

    private boolean existsAnnotation(Class<?>[] classes) {
        if (CollectionUtils.isNotEmpty(classes)) {
            for (Class<?> clazz : classes) {
                if (clazz == null) {
                    continue;
                }
                // 类上的GlobalTransactional注解
                GlobalTransactional trxAnno = clazz.getAnnotation(GlobalTransactional.class);
                if (trxAnno != null) {
                    return true;
                }
                Method[] methods = clazz.getMethods();
                for (Method method : methods) {
                    // 方法上GlobalTransactional注解
                    trxAnno = method.getAnnotation(GlobalTransactional.class);
                    if (trxAnno != null) {
                        return true;
                    }

                    // 方法上GlobalLock注解
                    GlobalLock lockAnno = method.getAnnotation(GlobalLock.class);
                    if (lockAnno != null) {
                        return true;
                    }
                }
            }
        }
        return false;
    }

4.3.3 返回拦截器

实现AbstractAutoProxyCreator类的方法返回拦截器：

    @Override
    protected Object[] getAdvicesAndAdvisorsForBean(Class beanClass, String beanName, TargetSource customTargetSource)
            throws BeansException {
        return new Object[]{interceptor};
    }

4.4 添加destory操作

4.4.1 实现DisposableBean接口

实现DisposableBean接口，调用ShutdownHook做destory操作：

    @Override
    public void destroy() {
        // 统一委托给ShutdownHook做destory，虽然它自己也可以做
        ShutdownHook.getInstance().destroyAll();
    }

4.4.2 注册shutdownhook

在init时注册shutdownhook

    private void registerSpringShutdownHook() {
        if (applicationContext instanceof ConfigurableApplicationContext) {
            ((ConfigurableApplicationContext) applicationContext).registerShutdownHook();
            // 这里移除了ShutdownHook注册的java虚拟机的shutdownhook
            ShutdownHook.removeRuntimeShutdownHook();
        }
        // TM客户端和RM客户端的父类实现了Disposable的destory方法，ShutdownHook遍历调用所有Disposable实现类的destory方法
        ShutdownHook.getInstance().addDisposable(TmNettyRemotingClient.getInstance(applicationId, txServiceGroup));
        ShutdownHook.getInstance().addDisposable(RmNettyRemotingClient.getInstance(applicationId, txServiceGroup));
    }

end.

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