// 依賴DataSource
@ConditionalOnBean(DataSource.class)
// 三個(gè)配置都要為true
@ConditionalOnExpression("${seata.enabled:true} && ${seata.enableAutoDataSourceProxy:true} && ${seata.enable-auto-data-source-proxy:true}")
@AutoConfigureAfter({SeataCoreAutoConfiguration.class})
public class SeataDataSourceAutoConfiguration {
    /**
     * The bean seataAutoDataSourceProxyCreator.
     */
    @Bean(BEAN_NAME_SEATA_AUTO_DATA_SOURCE_PROXY_CREATOR)
    // 可替換
    @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對(duì)象不代理
        if (!(bean instanceof DataSource)) {
            return bean;
        }
        // 如果是DataSource對(duì)象，但是不是SeataDataSourceProxy對(duì)象
        if (!(bean instanceof SeataDataSourceProxy)) {
            // 先調(diào)用父類包裝一層
            Object enhancer = super.wrapIfNecessary(bean, beanName, cacheKey);
            // 如果代理后的對(duì)象和代理前的對(duì)象是同一個(gè)對(duì)象
            // 說明要么這個(gè)對(duì)象之前已經(jīng)被代理過
            // 要么SeataDataSourceProxy被開發(fā)人員excluded
            if (bean == enhancer) {
                return bean;
            }
            // 如果是正常的DataSource對(duì)象的話，那么就會(huì)被自動(dòng)構(gòu)建成SeataDataSourceProxy，并返回
            DataSource origin = (DataSource) bean;
            SeataDataSourceProxy proxy = buildProxy(origin, dataSourceProxyMode);
            DataSourceProxyHolder.put(origin, proxy);
            return enhancer;
        }
        /*
         * things get dangerous when you try to register SeataDataSourceProxy bean by yourself!
         * if you insist on doing so, you must make sure your method return type is DataSource,
         * because this processor will never return any subclass of SeataDataSourceProxy
         */
        // Seata是不建議用戶自己構(gòu)建SeataDataSourceProxy對(duì)象的，即使用戶自己構(gòu)建了SeataDataSourceProxy對(duì)象，Seata也會(huì)重新處理
        LOGGER.warn("Manually register SeataDataSourceProxy(or its subclass) bean is discouraged! bean name: {}", beanName);
        // 獲取用戶包裝好的代理對(duì)象
        SeataDataSourceProxy proxy = (SeataDataSourceProxy) bean;
        // 獲取原生DataSource
        DataSource origin = proxy.getTargetDataSource();
        // 重新包裝，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);
        // 返回包裝好的代理對(duì)象SeataDataSourceProxy
        return originEnhancer;
    }
}

// 配置seata.enabled=true
@ConditionalOnProperty(prefix = SEATA_PREFIX, name = "enabled", havingValue = "true", matchIfMissing = true)
// 裝配順序
@AutoConfigureAfter({SeataCoreAutoConfiguration.class})
public class SeataAutoConfiguration {
    private static final Logger LOGGER = LoggerFactory.getLogger(SeataAutoConfiguration.class);
    @Bean(BEAN_NAME_FAILURE_HANDLER)
    // 失敗處理器，可替換
    @ConditionalOnMissingBean(FailureHandler.class)
    public FailureHandler failureHandler() {
        return new DefaultFailureHandlerImpl();
    }
    @Bean
    @DependsOn({BEAN_NAME_SPRING_APPLICATION_CONTEXT_PROVIDER, BEAN_NAME_FAILURE_HANDLER})
    // 開發(fā)人員可自定義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) {
        // 檢查Bean是否符合被代理的要求
        // 1. 不能是配置類，比如以Configuration、Properties、Config結(jié)尾的Bean名稱
        // 2. Bean所在的包名在掃描范圍內(nèi)
        // 3. 不能被@Scope注解
        if (!doCheckers(bean, beanName)) {
            return bean;
        }
        try {
            synchronized (PROXYED_SET) {
                // 如果已經(jīng)被代理，就跳過
                if (PROXYED_SET.contains(beanName)) {
                    return bean;
                }
                interceptor = null;
                // 檢查是否被TCC注解
                if (TCCBeanParserUtils.isTccAutoProxy(bean, beanName, applicationContext)) {
                    // 初始化TCC Fence Clean Task
                   TCCBeanParserUtils.initTccFenceCleanTask(TCCBeanParserUtils.getRemotingDesc(beanName), applicationContext);
                    // 創(chuàng)建TCC代理類
                    interceptor = new TccActionInterceptor(TCCBeanParserUtils.getRemotingDesc(beanName));
                    ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                            (ConfigurationChangeListener)interceptor);
                } else {
                    // 如果不是TCC代理，那么先獲取當(dāng)前類和它實(shí)現(xiàn)的接口
                    Class<?> serviceInterface = SpringProxyUtils.findTargetClass(bean);
                    Class<?>[] interfacesIfJdk = SpringProxyUtils.findInterfaces(bean);
                    // 判斷當(dāng)前類及相關(guān)方法是否被@GlobalTransactional或@GlobalLock注解
                    if (!existsAnnotation(new Class[]{serviceInterface})
                        && !existsAnnotation(interfacesIfJdk)) {
                        // 沒有被注解，不代理
                        return bean;
                    }
                  
                    // 準(zhǔn)備創(chuàng)建方法攔截器
                    if (globalTransactionalInterceptor == null) {
                        globalTransactionalInterceptor = new GlobalTransactionalInterceptor(failureHandlerHook);
                        ConfigurationCache.addConfigListener(
                                ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                                (ConfigurationChangeListener)globalTransactionalInterceptor);
                    }
                    // 攔截器創(chuàng)建完畢
                    interceptor = globalTransactionalInterceptor;
                }
                LOGGER.info("Bean[{}] with name [{}] would use interceptor [{}]", bean.getClass().getName(), beanName, interceptor.getClass().getName());
                // 如果bean不是代理對(duì)象，那么不做方法攔截，直接返回
                if (!AopUtils.isAopProxy(bean)) {
                    bean = super.wrapIfNecessary(bean, beanName, cacheKey);
                } else {
                    // 準(zhǔn)備把方法攔截器插入進(jìn)去
                    AdvisedSupport advised = SpringProxyUtils.getAdvisedSupport(bean);
                    // 獲取所有的方法攔截器，包括GlobalTransactionalInterceptor
                    Advisor[] advisor = buildAdvisors(beanName, getAdvicesAndAdvisorsForBean(null, null, null));
                    int pos;
                    // 依次添加進(jìn)目標(biāo)對(duì)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() {
        // 如果不允許全局事務(wù)
        if (disableGlobalTransaction) {
            if (LOGGER.isInfoEnabled()) {
                LOGGER.info("Global transaction is disabled.");
            }
          // 添加監(jiān)聽器，監(jiān)聽配置的變化
            ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,
                    (ConfigurationChangeListener)this);
            return;
        }
        
        if (initialized.compareAndSet(false, true)) {
          // 準(zhǔn)備初始化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 {
    // 注冊(cè)攔截器
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new TransactionPropagationInterceptor());
    }
  
    // 添加異常解析處理器
    @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);
    // 前置處理邏輯
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        // 獲取當(dāng)前線程XID
        String xid = RootContext.getXID();
        // 從rpc中獲取XID
        String rpcXid = request.getHeader(RootContext.KEY_XID);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("xid in RootContext[{}] xid in HttpContext[{}]", xid, rpcXid);
        }
        // 如果線程中沒有XID，并且從請(qǐng)求中拿到了XID，那么把請(qǐng)求中的XID綁定到當(dāng)前線程
        if (StringUtils.isBlank(xid) && StringUtils.isNotBlank(rpcXid)) {
            RootContext.bind(rpcXid);
            if (LOGGER.isDebugEnabled()) {
                LOGGER.debug("bind[{}] to RootContext", rpcXid);
            }
        }
        return true;
    }
    // 后置處理邏輯
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        // 業(yè)務(wù)邏輯處理完畢，從當(dāng)前線程中刪除XID
        if (RootContext.inGlobalTransaction()) {
            XidResource.cleanXid(request.getHeader(RootContext.KEY_XID));
        }
    }
}
public class HttpHandlerExceptionResolver extends AbstractHandlerExceptionResolver {
    // 發(fā)生異常后，刪除當(dāng)前線程中的XID
    @Override
    protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse httpServletResponse, Object o, Exception e) {
        XidResource.cleanXid(request.getHeader(RootContext.KEY_XID));
        return null;
    }
}