tcc分布式事务源码解析系列(四)之项目实战

通过之前的几篇文章我相信您已经搭建好了运行环境，本次的项目实战是依照happylifeplat-tcc-demo项目来演练，也是非常经典的分布式事务场景：支付成功，进行订单状态的更新，扣除用户账户，库存扣减这几个模块来进行tcc分布式事务。话不多说，让我们一起进入体验吧！

首先我们找到 PaymentServiceImpl.makePayment 方法，这是tcc分布式事务的发起者

//tcc分布式事务的发起者 @Tcc(confirmMethod = "confirmOrderStatus", cancelMethod = "cancelOrderStatus") public void makePayment(Order order) { order.setStatus(OrderStatusEnum.PAYING.getCode()); orderMapper.update(order); //扣除用户余额远端的rpc调用 AccountDTO accountDTO = new AccountDTO(); accountDTO.setAmount(order.getTotalAmount()); accountDTO.setUserId(order.getUserId()); accountService.payment(accountDTO); //进入扣减库存操作远端的rpc调用 InventoryDTO inventoryDTO = new InventoryDTO(); inventoryDTO.setCount(order.getCount()); inventoryDTO.setProductId(order.getProductId()); inventoryService.decrease(inventoryDTO); } //更新订单的confirm方法 public void confirmOrderStatus(Order order) { order.setStatus(OrderStatusEnum.PAY_SUCCESS.getCode()); orderMapper.update(order); LOGGER.info("=========进行订单confirm操作完成================"); } //更新订单的cancel方法 public void cancelOrderStatus(Order order) { order.setStatus(OrderStatusEnum.PAY_FAIL.getCode()); orderMapper.update(order); LOGGER.info("=========进行订单cancel操作完成================"); }
makePayment 方法是tcc分布式事务的发起者，它里面有更新订单状态（本地），进行库存扣减（rpc扣减），资金扣减(rpc调用)
confirmOrderStatus 为订单状态confirm方法，cancelOrderStatus 为订单状态cancel方法。
我们重点关注 @Tcc(confirmMethod = "confirmOrderStatus", cancelMethod = "cancelOrderStatus") 这个注解，为什么加了这个注解就有神奇的作用。

@Tcc注解切面

我们找到在happylifeplat-tcc-core包中找到 TccTransactionAspect，这里定义@Tcc的切点。

@Aspect public abstract class TccTransactionAspect {

private TccTransactionInterceptor tccTransactionInterceptor;

public void setTccTransactionInterceptor(TccTransactionInterceptor tccTransactionInterceptor) {
    this.tccTransactionInterceptor = tccTransactionInterceptor;
}

@Pointcut("@annotation(com.happylifeplat.tcc.annotation.Tcc)")
public void txTransactionInterceptor() {

}

@Around("txTransactionInterceptor()")
public Object interceptCompensableMethod(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
    return tccTransactionInterceptor.interceptor(proceedingJoinPoint);
}

public abstract int getOrder();

}

我们可以知道Spring实现类的方法凡是加了@Tcc注解的，在调用的时候，都会进行 tccTransactionInterceptor.interceptor 调用。

其次我们发现该类是一个抽象类，肯定会有其他类继承它，你猜的没错，对应dubbo用户，他的继承类为:

@Aspect @Component public class DubboTccTransactionAspect extends TccTransactionAspect implements Ordered {

@Autowired
public DubboTccTransactionAspect(DubboTccTransactionInterceptor dubboTccTransactionInterceptor) {
    super.setTccTransactionInterceptor(dubboTccTransactionInterceptor);
}


@Override
public int getOrder() {
    return Ordered.HIGHEST_PRECEDENCE;
}

}

springcloud的用户,它的继承类为:

@Aspect @Component public class SpringCloudTxTransactionAspect extends TccTransactionAspect implements Ordered {

@Autowired
public SpringCloudTxTransactionAspect(SpringCloudTxTransactionInterceptor  springCloudTxTransactionInterceptor) {
    this.setTccTransactionInterceptor(springCloudTxTransactionInterceptor);
}


public void init() {

}

@Override
public int getOrder() {
    return Ordered.HIGHEST_PRECEDENCE;
}

}

我们注意到他们都实现了Spring的Ordered接口，并重写了 getOrder 方法，都返回了 Ordered.HIGHEST_PRECEDENCE 那么可以知道，他是优先级最高的切面。

TccCoordinatorMethodAspect 切面

@Aspect
@Component
public class TccCoordinatorMethodAspect implements Ordered {


    private final TccCoordinatorMethodInterceptor tccCoordinatorMethodInterceptor;

    @Autowired
    public TccCoordinatorMethodAspect(TccCoordinatorMethodInterceptor tccCoordinatorMethodInterceptor) {
        this.tccCoordinatorMethodInterceptor = tccCoordinatorMethodInterceptor;
    }


    @Pointcut("@annotation(com.happylifeplat.tcc.annotation.Tcc)")
    public void coordinatorMethod() {

    }

    @Around("coordinatorMethod()")
    public Object interceptCompensableMethod(ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
        return tccCoordinatorMethodInterceptor.interceptor(proceedingJoinPoint);
    }


    @Override
    public int getOrder() {
        return Ordered.HIGHEST_PRECEDENCE + 1;
    }
}

该切面是第二优先级的切面，意思就是当我们对有@Tcc注解的方法发起调用的时候，首先会进入 TccTransactionAspect 切面，然后再进入 TccCoordinatorMethodAspect 切面。该切面主要是用来获取@Tcc注解上的元数据，比如confrim方法名称等等。
到这里如果大家基本能明白的话，差不多就了解了整个框架原理，现在让我们来跟踪调用吧。

现在我们回过头，我们来调用 PaymentServiceImpl.makePayment 方法

dubbo用户，我们会进入如下拦截器:

@Component public class DubboTccTransactionInterceptor implements TccTransactionInterceptor {

private final TccTransactionAspectService tccTransactionAspectService;

@Autowired
public DubboTccTransactionInterceptor(TccTransactionAspectService tccTransactionAspectService) {
    this.tccTransactionAspectService = tccTransactionAspectService;
}


@Override
public Object interceptor(ProceedingJoinPoint pjp) throws Throwable {
    final String context = RpcContext.getContext().getAttachment(Constant.TCC_TRANSACTION_CONTEXT);
    TccTransactionContext tccTransactionContext = null;
    if (StringUtils.isNoneBlank(context)) {
        tccTransactionContext =
                GsonUtils.getInstance().fromJson(context, TccTransactionContext.class);
    }
    return tccTransactionAspectService.invoke(tccTransactionContext, pjp);
}

}

我们继续跟踪 tccTransactionAspectService.invoke(tccTransactionContext, pjp) ,发现通过判断过后，我们会进入 StartTccTransactionHandler.handler 方法,我们已经进入了分布式事务处理的入口了！

/** * 分布式事务处理接口 * * @param point point 切点 * @param context 信息 * @return Object * @throws Throwable 异常 */ @Override public Object handler(ProceedingJoinPoint point, TccTransactionContext context) throws Throwable { Object returnValue; try { //开启分布式事务 tccTransactionManager.begin(); try { //发起调用执行try方法 returnValue = point.proceed(); } catch (Throwable throwable) { //异常执行cancel tccTransactionManager.cancel(); throw throwable; } //try成功执行confirm confirm 失败的话，那就只能走本地补偿 tccTransactionManager.confirm(); } finally { tccTransactionManager.remove(); } return returnValue; }
我们进行跟进 tccTransactionManager.begin() 方法:

/** * 该方法为发起方第一次调用 * 也是tcc事务的入口 */ void begin() { LogUtil.debug(LOGGER, () -> "开始执行tcc事务！start"); TccTransaction tccTransaction = CURRENT.get(); if (Objects.isNull(tccTransaction)) { tccTransaction = new TccTransaction(); tccTransaction.setStatus(TccActionEnum.TRYING.getCode()); tccTransaction.setRole(TccRoleEnum.START.getCode()); } //保存当前事务信息 coordinatorCommand.execute(new CoordinatorAction(CoordinatorActionEnum.SAVE, tccTransaction)); CURRENT.set(tccTransaction); //设置tcc事务上下文，这个类会传递给远端 TccTransactionContext context = new TccTransactionContext(); context.setAction(TccActionEnum.TRYING.getCode());//设置执行动作为try context.setTransId(tccTransaction.getTransId());//设置事务id TransactionContextLocal.getInstance().set(context); }
这里我们保存了事务信息，并且开启了事务上下文，并把它保存在了ThreadLoacl里面，大家想想这里为什么一定要保存在ThreadLocal里面。

begin方法执行完后，我们回到切面，现在我们来执行 **point.proceed()**，当执行这一句代码的时候，会进入第二个切面，即进入了 TccCoordinatorMethodInterceptor

public Object interceptor(ProceedingJoinPoint pjp) throws Throwable {

   final TccTransaction currentTransaction = tccTransactionManager.getCurrentTransaction();

   if (Objects.nonNull(currentTransaction)) {
       final TccActionEnum action = TccActionEnum.acquireByCode(currentTransaction.getStatus());
       switch (action) {
           case TRYING:
               registerParticipant(pjp, currentTransaction.getTransId());
               break;
           case CONFIRMING:
               break;
           case CANCELING:
               break;
       }
   }
   return pjp.proceed(pjp.getArgs());

}

这里由于是在try阶段，直接就进入了 registerParticipant 方法

private void registerParticipant(ProceedingJoinPoint point, String transId) throws NoSuchMethodException {
```
    MethodSignature signature = (MethodSignature) point.getSignature();
    Method method = signature.getMethod();

    Class<?> clazz = point.getTarget().getClass();

    Object[] args = point.getArgs();

    final Tcc tcc = method.getAnnotation(Tcc.class);

    //获取协调方法
    String confirmMethodName = tcc.confirmMethod();

   /* if (StringUtils.isBlank(confirmMethodName)) {
        confirmMethodName = method.getName();
    }*/

    String cancelMethodName = tcc.cancelMethod();

   /* if (StringUtils.isBlank(cancelMethodName)) {
        cancelMethodName = method.getName();
    }
```
*/ //设置模式 final TccPatternEnum pattern = tcc.pattern(); tccTransactionManager.getCurrentTransaction().setPattern(pattern.getCode()); TccInvocation confirmInvocation = null; if (StringUtils.isNoneBlank(confirmMethodName)) { confirmInvocation = new TccInvocation(clazz, confirmMethodName, method.getParameterTypes(), args); } TccInvocation cancelInvocation = null; if (StringUtils.isNoneBlank(cancelMethodName)) { cancelInvocation = new TccInvocation(clazz, cancelMethodName, method.getParameterTypes(), args); } //封装调用点 final Participant participant = new Participant( transId, confirmInvocation, cancelInvocation); tccTransactionManager.enlistParticipant(participant); }
这里就获取了 @Tcc(confirmMethod = "confirmOrderStatus", cancelMethod = "cancelOrderStatus") 的信息，并把他封装成了 Participant，存起来，然后真正的调用 PaymentServiceImpl.makePayment 业务方法，在业务方法里面，我们首先执行的是更新订单状态（相信现在你还记得0.0）:
```
   order.setStatus(OrderStatusEnum.PAYING.getCode());
   orderMapper.update(order);
```

接下来，我们进行扣除用户余额,注意扣除余额这里是一个rpc方法：

   AccountDTO accountDTO = new AccountDTO();
   accountDTO.setAmount(order.getTotalAmount());
   accountDTO.setUserId(order.getUserId());
   accountService.payment(accountDTO)

现在我们来关注 accountService.payment(accountDTO) ，这个接口的定义。

dubbo接口:

public interface AccountService {


    /**
     * 扣款支付
     *
     * @param accountDTO 参数dto
     * @return true
     */
    @Tcc
    boolean payment(AccountDTO accountDTO);
}

springcloud接口

@FeignClient(value = "account-service", configuration = MyConfiguration.class)
public interface AccountClient {

    @PostMapping("/account-service/account/payment")
    @Tcc
    Boolean payment(@RequestBody AccountDTO accountDO);

}

很明显这里我们都在接口上加了@Tcc注解，我们知道springAop的特性，在接口上加注解，是无法进入切面的，所以我们在这里，要采用rpc框架的某些特性来帮助我们获取到 @Tcc注解信息。这一步很重要。当我们发起

accountService.payment(accountDTO) 调用的时候:

dubbo用户，会走dubbo的filter接口,TccTransactionFilter:

private void registerParticipant(Class clazz, String methodName, Object[] arguments, Class... args) throws TccRuntimeException { try { Method method = clazz.getDeclaredMethod(methodName, args); Tcc tcc = method.getAnnotation(Tcc.class); if (Objects.nonNull(tcc)) { //获取事务的上下文 final TccTransactionContext tccTransactionContext = TransactionContextLocal.getInstance().get(); if (Objects.nonNull(tccTransactionContext)) { //dubbo rpc传参数 RpcContext.getContext() .setAttachment(Constant.TCC_TRANSACTION_CONTEXT, GsonUtils.getInstance().toJson(tccTransactionContext)); } if (Objects.nonNull(tccTransactionContext)) { if(TccActionEnum.TRYING.getCode()==tccTransactionContext.getAction()){ //获取协调方法 String confirmMethodName = tcc.confirmMethod(); if (StringUtils.isBlank(confirmMethodName)) { confirmMethodName = method.getName(); } String cancelMethodName = tcc.cancelMethod(); if (StringUtils.isBlank(cancelMethodName)) { cancelMethodName = method.getName(); } //设置模式 final TccPatternEnum pattern = tcc.pattern(); tccTransactionManager.getCurrentTransaction().setPattern(pattern.getCode()); TccInvocation confirmInvocation = new TccInvocation(clazz, confirmMethodName, args, arguments); TccInvocation cancelInvocation = new TccInvocation(clazz, cancelMethodName, args, arguments); //封装调用点 final Participant participant = new Participant( tccTransactionContext.getTransId(), confirmInvocation, cancelInvocation); tccTransactionManager.enlistParticipant(participant); } } } } catch (NoSuchMethodException e) { throw new TccRuntimeException("not fount method " + e.getMessage()); } }
springcloud 用户，则会进入 TccFeignHandler ：

public class TccFeignHandler implements InvocationHandler { /** * logger */ private static final Logger LOGGER = LoggerFactory.getLogger(TccFeignHandler.class); private Target target; private Map handlers; public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (Object.class.equals(method.getDeclaringClass())) { return method.invoke(this, args); } else { final Tcc tcc = method.getAnnotation(Tcc.class); if (Objects.isNull(tcc)) { return this.handlers.get(method).invoke(args); } final TccTransactionContext tccTransactionContext = TransactionContextLocal.getInstance().get(); if (Objects.nonNull(tccTransactionContext)) { final TccTransactionManager tccTransactionManager = SpringBeanUtils.getInstance().getBean(TccTransactionManager.class); if (TccActionEnum.TRYING.getCode() == tccTransactionContext.getAction()) { //获取协调方法 String confirmMethodName = tcc.confirmMethod(); if (StringUtils.isBlank(confirmMethodName)) { confirmMethodName = method.getName(); } String cancelMethodName = tcc.cancelMethod(); if (StringUtils.isBlank(cancelMethodName)) { cancelMethodName = method.getName(); } //设置模式 final TccPatternEnum pattern = tcc.pattern(); tccTransactionManager.getCurrentTransaction().setPattern(pattern.getCode()); final Class declaringClass = method.getDeclaringClass(); TccInvocation confirmInvocation = new TccInvocation(declaringClass, confirmMethodName, method.getParameterTypes(), args); TccInvocation cancelInvocation = new TccInvocation(declaringClass, cancelMethodName, method.getParameterTypes(), args); //封装调用点 final Participant participant = new Participant( tccTransactionContext.getTransId(), confirmInvocation, cancelInvocation); tccTransactionManager.enlistParticipant(participant); } } return this.handlers.get(method).invoke(args); } } public void setTarget(Target<?> target) { this.target = target; } public void setHandlers(Map<Method, MethodHandler> handlers) { this.handlers = handlers; } }