Seata AT模式启动过程图文示例详解

// 依赖DataSource
@ConditionalOnBean(DataSource.class)
// 三个配置都要为true
@ConditionalOnExpression("${seata.enabled:true} && ${seata.enableAutoDataSourceProxy:true} && ${seata.enable-auto-data-source-proxy:true}")
@AutoConfigureAfter({SeataCoreAutoConfiguration.class})
public class SeataDataSourceAutoConfiguration {
    
    @Bean(BEAN_NAME_SEATA_AUTO_DATA_SOURCE_PROXY_CREATOR)
    // 可替换
    @ConditionalOnMissingBean(SeataAutoDataSourceProxyCreator.class)
    public SeataAutoDataSourceProxyCreator seataAutoDataSourceProxyCreator(SeataProperties seataProperties) {
        return new SeataAutoDataSourceProxyCreator(seataProperties.isUsejdkProxy(),
            seataProperties.getExcludesForAutoProxying(), seataProperties.getDataSourceProxyMode());
    }
}

public class SeataAutoDataSourceProxyCreator extends AbstractAutoProxyCreator {
  @Override
    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        // 不是DataSource对象不代理
        if (!(bean instanceof DataSource)) {
            return bean;
        }
        // 如果是DataSource对象，但是不是SeataDataSourceProxy对象
        if (!(bean instanceof SeataDataSourceProxy)) {
            // 先调用父类包装一层
            Object enhancer = super.wrapIfNecessary(bean, beanName, cacheKey);
            // 如果代理后的对象和代理前的对象是同一个对象
            // 说明要么这个对象之前已经被代理过
            // 要么SeataDataSourceProxy被开发人员excluded
            if (bean == enhancer) {
                return bean;
            }
            // 如果是正常的DataSource对象的话，那么就会被自动构建成SeataDataSourceProxy，并返回
            DataSource origin = (DataSource) bean;
            SeataDataSourceProxy proxy = buildProxy(origin, dataSourceProxyMode);
            DataSourceProxyHolder.put(origin, proxy);
            return enhancer;
        }
        
        // Seata是不建议用户自己构建SeataDataSourceProxy对象的，即使用户自己构建了SeataDataSourceProxy对象，Seata也会重新处理
        LOGGER.warn("Manually reGISter SeataDataSourceProxy(or its subclass) bean is discouraged! bean name: {}", beanName);
        // 获取用户包装好的代理对象
        SeataDataSourceProxy proxy = (SeataDataSourceProxy) bean;
        // 获取原生DataSource
        DataSource origin = proxy.getTargetDataSource();
        // 重新包装，并返回
        Object originEnhancer = super.wrapIfNecessary(origin, beanName, cacheKey);
        // this mean origin is either excluded by user or had been proxy before
        if (origin == originEnhancer) {
            return origin;
        }
        // else, put <origin, proxy> to holder and return originEnhancer
        DataSourceProxyHolder.put(origin, proxy);
        // 返回包装好的代理对象SeataDataSourceProxy
        return originEnhancer;
    }
}

// 配置seata.enabled=true
@ConditionalOnProperty(prefix = SEATA_PREFIX, name = "enabled", havingValue = "true", matchIfMissing = true)
// 装配顺序
@AutoConfigureAfter({SeataCoreAutoConfiguration.class})
public class SeataAutoConfiguration {
    private static final Logger LOGGER = LoggerFactory.getLogger(SeataAutoConfiguration.class);
    @Bean(BEAN_NAME_FaiLURE_HANDLER)
    // 失败处理器，可替换
    @ConditionalOnMissingBean(FailureHandler.class)
    public FailureHandler failureHandler() {
        return new DefaultFailureHandlerImpl();
    }
    @Bean
    @DependsOn({BEAN_NAME_SPRING_APPLICATION_CONTEXT_PROVIDER, BEAN_NAME_FAILURE_HANDLER})
    // 开发人员可自定义GlobalTransactionScanner
    @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());
        //set accessKey and secreTKEy
        GlobalTransactionScanner.setAccessKey(seataProperties.getAccessKey());
        GlobalTransactionScanner.setSecretKey(seataProperties.getSecretKey());
        // create global transaction scanner
        return new GlobalTransactionScanner(seataProperties.getApplicationId(), seataProperties.getTxServiceGroup(), failureHandler);
    }
}

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

@Override
    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        // 检查Bean是否符合被代理的要求
        // 1. 不能是配置类，比如以Configuration、Properties、Config结尾的Bean名称
        // 2. Bean所在的包名在扫描范围内
        // 3. 不能被@Scope注解
        if (!doCheckers(bean, beanName)) {
            return bean;
        }
        try {
            synchronized (PROXYED_SET) {
                // 如果已经被代理，就跳过
                if (PROXYED_SET.contains(beanName)) {
                    return bean;
                }
                interceptor = null;
                // 检查是否被TCC注解
                if (TCCBeanParserUtils.isTccAutoProxy(bean, beanName, applicationContext)) {
                    // 初始化TCC Fence Clean Task
                   TCCBeanParserUtils.initTccFenceCleanTask(TCCBeanParserUtils.getRemotingDesc(beanName), applicationContext);
                    // 创建TCC代理类
                    interceptor = new TccActionInterceptor(TCCBeanParserUtils.getRemotingDesc(beanName));
                    ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                            (ConfigurationChangeListener)interceptor);
                } else {
                    // 如果不是TCC代理，那么先获取当前类和它实现的接口
                    Class<?> serviceInterface = SpringProxyUtils.findTargetClass(bean);
                    Class<?>[] interfacesIfJdk = SpringProxyUtils.findInterfaces(bean);
                    // 判断当前类及相关方法是否被@GlobalTransactional或@GlobalLock注解
                    if (!existsAnnotation(new Class[]{serviceInterface})
                        && !existsAnnotation(interfacesIfJdk)) {
                        // 没有被注解，不代理
                        return bean;
                    }
                  
                    // 准备创建方法拦截器
                    if (globalTransactionalInterceptor == null) {
                        globalTransactionalInterceptor = new GlobalTransactionalInterceptor(failureHandlerHook);
                        ConfigurationCache.addConfigListener(
                                ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                                (ConfigurationChangeListener)globalTransactionalInterceptor);
                    }
                    // 拦截器创建完毕
                    interceptor = globalTransactionalInterceptor;
                }
                LOGGER.info("Bean[{}] with name [{}] would use interceptor [{}]", bean.getClass().getName(), beanName, interceptor.getClass().getName());
                // 如果bean不是代理对象，那么不做方法拦截，直接返回
                if (!AopUtils.isAopProxy(bean)) {
                    bean = super.wrapIfNecessary(bean, beanName, cacheKey);
                } else {
                    // 准备把方法拦截器插入进去
                    AdvisedSupport advised = SpringProxyUtils.getAdvisedSupport(bean);
                    // 获取所有的方法拦截器，包括GlobalTransactionalInterceptor
                    Advisor[] advisor = buildAdvisors(beanName, getAdvicesAndAdvisorsForBean(null, null, null));
                    int pos;
                    // 依次添加进目标对象中
                    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);
                // 返回被代理的bean
                return bean;
            }
        } catch (Exception exx) {
            throw new RuntimeException(exx);
        }
    }

@Override
    public void afterPropertiesSet() {
        // 如果不允许全局事务
        if (disableGlobalTransaction) {
            if (LOGGER.isInfoEnabled()) {
                LOGGER.info("Global transaction is disabled.");
            }
          // 添加监听器，监听配置的变化
            ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                    (ConfigurationChangeListener)this);
            return;
        }
        
        if (initialized.compareAndSet(false, true)) {
          // 准备初始化TM Client、RM Client
            initClient();
        }
    }
private void initClient() {
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Initializing Global Transaction Clients ... ");
        }
        if (DEFAULT_TX_GROUP_OLD.equals(txServiceGroup)) {
            LOGGER.warn("the default value of seata.tx-service-group: {} has already changed to {} since Seata 1.5, " +
                    "please change your default configuration as soon as possible " +
                    "and we don't recommend you to use default tx-service-group's value provided by seata",
                    DEFAULT_TX_GROUP_OLD, DEFAULT_TX_GROUP);
        }
        if (StringUtils.isNullOrEmpty(applicationId) || StringUtils.isNullOrEmpty(txServiceGroup)) {
            throw new IllegalArgumentException(String.fORMat("applicationId: %s, txServiceGroup: %s", applicationId, txServiceGroup));
        }
        //初始化TM Client
        TMClient.init(applicationId, txServiceGroup, accessKey, secretKey);
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Transaction Manager Client is initialized. applicationId[{}] txServiceGroup[{}]", applicationId, txServiceGroup);
        }
        //初始化RM Client
        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();
    }

@Configuration(proxyBeanMethods = false)
@ConditionalOnWEBApplication
public class HttpAutoConfiguration extends WebmvcConfigurerAdapter {
    // 注册拦截器
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new TransactionPropagationInterceptor());
    }
  
    // 添加异常解析处理器
    @Override
    public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
        exceptionResolvers.add(new HttpHandlerExceptionResolver());
    }
}
public class TransactionPropagationInterceptor extends HandlerInterceptorAdapter {
    private static final Logger LOGGER = LoggerFactory.getLogger(TransactionPropagationInterceptor.class);
    // 前置处理逻辑
    @Override
    public boolean preHandle(httpservletRequest request, HttpServletResponse response, Object handler) {
        // 获取当前线程XID
        String xid = RootContext.getXID();
        // 从rpc中获取XID
        String rpcXid = request.getHeader(RootContext.KEY_XID);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("xid in RootContext[{}] xid in HttpContext[{}]", xid, rpcXid);
        }
        // 如果线程中没有XID，并且从请求中拿到了XID，那么把请求中的XID绑定到当前线程
        if (StringUtils.isBlank(xid) && StringUtils.isNotBlank(rpcXid)) {
            RootContext.bind(rpcXid);
            if (LOGGER.isDebugEnabled()) {
                LOGGER.debug("bind[{}] to RootContext", rpcXid);
            }
        }
        return true;
    }
    // 后置处理逻辑
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        // 业务逻辑处理完毕，从当前线程中删除XID
        if (RootContext.inGlobalTransaction()) {
            XidResource.cleanXid(request.getHeader(RootContext.KEY_XID));
        }
    }
}
public class HttpHandlerExceptionResolver extends AbstractHandlerExceptionResolver {
    // 发生异常后，删除当前线程中的XID
    @Override
    protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse httpServletResponse, Object o, Exception e) {
        XidResource.cleanXid(request.getHeader(RootContext.KEY_XID));
        return null;
    }
}