原理

TM两阶段：

阶段1：TM向TC申请全局事务，netty客户端发起了一次记录xid的请求

阶段2：TC协调之后，决定执行RM是否提交或者回滚。

spring公共组件部分

1、SeataAutoConfiguration类

利用springboot自动装配机制从spring.factories文件加载自动配置类SeataAutoConfiguration

org.springframework.boot.autoconfigure.EnableAutoConfiguration=io.seata.spring.boot.autoconfigure.SeataAutoConfiguration

@ConditionalOnProperty(prefix = SEATA_PREFIX, name = "enabled", havingValue = "true", matchIfMissing = true)
@AutoConfigureAfter({SeataCoreAutoConfiguration.class})
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,
            ConfigurableListableBeanFactory beanFactory,
            @Autowired(required = false) List<ScannerChecker> scannerCheckers) {
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Automatically configure Seata");
        }

        // set bean factory
        GlobalTransactionScanner.setBeanFactory(beanFactory);

        // add checkers
        // '/META-INF/services/io.seata.spring.annotation.ScannerChecker'
        GlobalTransactionScanner.addScannerCheckers(EnhancedServiceLoader.loadAll(ScannerChecker.class));
        // spring beans
        GlobalTransactionScanner.addScannerCheckers(scannerCheckers);

        // add scannable packages
        GlobalTransactionScanner.addScannablePackages(seataProperties.getScanPackages());
        // add excludeBeanNames
        GlobalTransactionScanner.addScannerExcludeBeanNames(seataProperties.getExcludesForScanning());

        // create global transaction scanner
        return new GlobalTransactionScanner(seataProperties.getApplicationId(), seataProperties.getTxServiceGroup(), failureHandler);
    }
}

2、 GlobalTransactionScanner类

public class GlobalTransactionScanner extends AbstractAutoProxyCreator
        implements ConfigurationChangeListener, InitializingBean, ApplicationContextAware, DisposableBean

初始化TM、RM的netty客户端，提供aop能力

2-1、初始化TM、RM的netty客户端

io.seata.spring.annotation.GlobalTransactionScanner#afterPropertiesSet

spring-bean初始化赋值回调，这里初始化TM、RM的netty客户端，为后续发起请求做准备。

    @Override
    public void afterPropertiesSet() {
        if (disableGlobalTransaction) {
            if (LOGGER.isInfoEnabled()) {
                LOGGER.info("Global transaction is disabled.");
            }
            ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                    (ConfigurationChangeListener)this);
            return;
        }
        if (initialized.compareAndSet(false, true)) {
            initClient();
        }
    }

   private void initClient() {
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Initializing Global Transaction Clients ... ");
        }
        if (StringUtils.isNullOrEmpty(applicationId) || StringUtils.isNullOrEmpty(txServiceGroup)) {
            throw new IllegalArgumentException(String.format("applicationId: %s, txServiceGroup: %s", applicationId, txServiceGroup));
        }
        //init TM
        TMClient.init(applicationId, txServiceGroup, accessKey, secretKey);
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Transaction Manager Client is initialized. applicationId[{}] txServiceGroup[{}]", applicationId, txServiceGroup);
        }
        //init RM
        RMClient.init(applicationId, txServiceGroup);
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Resource Manager is initialized. applicationId[{}] txServiceGroup[{}]", applicationId, txServiceGroup);
        }

        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Global Transaction Clients are initialized. ");
        }
        registerSpringShutdownHook();

    }

2-2、aop代理实现

io.seata.spring.annotation.GlobalTransactionScanner#wrapIfNecessary，递归调用适配代理，Seata重写了这个方法，TCC代理、AT代理使用的还是spring那一套代理区分方式（jdk还是cglib）

    /**
     * The following will be scanned, and added corresponding interceptor:
     *
     * TM:
     * @see io.seata.spring.annotation.GlobalTransactional // TM annotation
     * Corresponding interceptor:
     * @see io.seata.spring.annotation.GlobalTransactionalInterceptor#handleGlobalTransaction(MethodInvocation, AspectTransactional) // TM handler
     *
     * GlobalLock:
     * @see io.seata.spring.annotation.GlobalLock // GlobalLock annotation
     * Corresponding interceptor:
     * @see io.seata.spring.annotation.GlobalTransactionalInterceptor#handleGlobalLock(MethodInvocation, GlobalLock)  // GlobalLock handler
     *
     * TCC mode:
     * @see io.seata.rm.tcc.api.LocalTCC // TCC annotation on interface
     * @see io.seata.rm.tcc.api.TwoPhaseBusinessAction // TCC annotation on try method
     * @see io.seata.rm.tcc.remoting.RemotingParser // Remote TCC service parser
     * Corresponding interceptor:
     * @see io.seata.spring.tcc.TccActionInterceptor // the interceptor of TCC mode
     */
    @Override
    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        // do checkers
        if (!doCheckers(bean, beanName)) {
            return bean;
        }

        try {
            synchronized (PROXYED_SET) {
                if (PROXYED_SET.contains(beanName)) {
                    return bean;
                }
                interceptor = null;
                //check TCC proxy
                if (TCCBeanParserUtils.isTccAutoProxy(bean, beanName, applicationContext)) {
                    // init tcc fence clean task if enable useTccFence
                    TCCBeanParserUtils.initTccFenceCleanTask(TCCBeanParserUtils.getRemotingDesc(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);
                        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));
                    int pos;
                    for (Advisor avr : advisor) {
                        // Find the position based on the advisor's order, and add to advisors by pos
                        pos = findAddSeataAdvisorPosition(advised, avr);
                        advised.addAdvisor(pos, avr);
                    }
                }
                PROXYED_SET.add(beanName);
                return bean;
            }
        } catch (Exception exx) {
            throw new RuntimeException(exx);
        }
    }

3、GlobalTransactionalInterceptor类