本篇内容主要讲解“Saga模式源码方法教程”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Saga模式源码方法教程”吧!
状态机定义
以一个典型的电商购物流程为例，我们定义3个服务，订单服务(OrderServer)，账户服务(AccountService)和库存服务(StorageService),这里我们把订单服务当做聚合服务，也就是TM。
当外部下单时，订单服务首先会创建一个订单，然后调用账户服务扣减金额，最后调用库存服务扣减库存。这个流程入下图：
seata的saga模式是基于状态机来实现了，状态机对状态的控制需要一个JSON文件，这个JSON文件定义如下：
{ "Name": "buyGoodsOnline", "Comment": "buy a goods on line, add order, deduct account, deduct storage ", "StartState": "SaveOrder", "Version": "0.0.1", "States": { "SaveOrder": { "Type": "ServiceTask", "ServiceName": "orderSave", "ServiceMethod": "saveOrder", "CompensateState": "DeleteOrder", "Next": "ChoiceAccountState", "Input": [ "$.[businessKey]", "$.[order]" ], "Output": { "SaveOrderResult": "$.#root" }, "Status": { "#root == true": "SU", "#root == false": "FA", "$Exception{java.lang.Throwable}": "UN" } }, "ChoiceAccountState":{ "Type": "Choice", "Choices":[ { "Expression":"[SaveOrderResult] == true", "Next":"ReduceAccount" } ], "Default":"Fail" }, "ReduceAccount": { "Type": "ServiceTask", "ServiceName": "accountService", "ServiceMethod": "decrease", "CompensateState": "CompensateReduceAccount", "Next": "ChoiceStorageState", "Input": [ "$.[businessKey]", "$.[userId]", "$.[money]", { "throwException" : "$.[mockReduceAccountFail]" } ], "Output": { "ReduceAccountResult": "$.#root" }, "Status": { "#root == true": "SU", "#root == false": "FA", "$Exception{java.lang.Throwable}": "UN" }, "Catch": [ { "Exceptions": [ "java.lang.Throwable" ], "Next": "CompensationTrigger" } ] }, "ChoiceStorageState":{ "Type": "Choice", "Choices":[ { "Expression":"[ReduceAccountResult] == true", "Next":"ReduceStorage" } ], "Default":"Fail" }, "ReduceStorage": { "Type": "ServiceTask", "ServiceName": "storageService", "ServiceMethod": "decrease", "CompensateState": "CompensateReduceStorage", "Input": [ "$.[businessKey]", "$.[productId]", "$.[count]", { "throwException" : "$.[mockReduceStorageFail]" } ], "Output": { "ReduceStorageResult": "$.#root" }, "Status": { "#root == true": "SU", "#root == false": "FA", "$Exception{java.lang.Throwable}": "UN" }, "Catch": [ { "Exceptions": [ "java.lang.Throwable" ], "Next": "CompensationTrigger" } ], "Next": "Succeed" }, "DeleteOrder": { "Type": "ServiceTask", "ServiceName": "orderSave", "ServiceMethod": "deleteOrder", "Input": [ "$.[businessKey]", "$.[order]" ] }, "CompensateReduceAccount": { "Type": "ServiceTask", "ServiceName": "accountService", "ServiceMethod": "compensateDecrease", "Input": [ "$.[businessKey]", "$.[userId]", "$.[money]" ] }, "CompensateReduceStorage": { "Type": "ServiceTask", "ServiceName": "storageService", "ServiceMethod": "compensateDecrease", "Input": [ "$.[businessKey]", "$.[productId]", "$.[count]" ] }, "CompensationTrigger": { "Type": "CompensationTrigger", "Next": "Fail" }, "Succeed": { "Type":"Succeed" }, "Fail": { "Type":"Fail", "ErrorCode": "PURCHASE_FAILED", "Message": "purchase failed" } } }状态机是运行在TM中的，也就是我们上面定义的订单服务。订单服务创建订单时需要开启一个全局事务，这时就需要启动状态机，代码如下：
StateMachineEngine stateMachineEngine = (StateMachineEngine) ApplicationContextUtils.getApplicationContext().getBean("stateMachineEngine"); Map<String, Object> startParams = new HashMap<>(3); String businessKey = String.valueOf(System.currentTimeMillis()); startParams.put("businessKey", businessKey); startParams.put("order", order); startParams.put("mockReduceAccountFail", "true"); startParams.put("userId", order.getUserId()); startParams.put("money", order.getPayAmount()); startParams.put("productId", order.getProductId()); startParams.put("count", order.getCount()); //sync test StateMachineInstance inst = stateMachineEngine.startWithBusinessKey("buyGoodsOnline", null, businessKey, startParams);可以看到，上面代码定义的buyGoodsOnline，正是JSON文件中name的属性值。
状态机初始化
那上面创建订单代码中的stateMachineEngine这个bean是在哪里定义的呢?订单服务的demo中有一个类StateMachineConfiguration来进行定义，代码如下：
public class StateMachineConfiguration { @Bean public ThreadPoolExecutorFactoryBean threadExecutor(){ ThreadPoolExecutorFactoryBean threadExecutor = new ThreadPoolExecutorFactoryBean(); threadExecutor.setThreadNamePrefix("SAGA_ASYNC_EXE_"); threadExecutor.setCorePoolSize(1); threadExecutor.setMaxPoolSize(20); return threadExecutor; } @Bean public DbStateMachineConfig dbStateMachineConfig(ThreadPoolExecutorFactoryBean threadExecutor, DataSource hikariDataSource) throws IOException { DbStateMachineConfig dbStateMachineConfig = new DbStateMachineConfig(); dbStateMachineConfig.setDataSource(hikariDataSource); dbStateMachineConfig.setThreadPoolExecutor((ThreadPoolExecutor) threadExecutor.getObject()); /** *这里配置了json文件的路径，TM在初始化的时候，会把json文件解析成StateMachineImpl类，如果数据库没有保存这个状态机，则存入数据库seata_state_machine_def表， *如果数据库有记录，则取最新的一条记录，并且注册到StateMachineRepositoryImpl， *注册的Map有2个，一个是stateMachineMapByNameAndTenant，key格式是(stateMachineName + "_" + tenantId), *一个是stateMachineMapById，key是stateMachine.getId() *具体代码见StateMachineRepositoryImpl类registryStateMachine方法 *这个注册的触发方法在DefaultStateMachineConfig的初始化方法init()，这个类是DbStateMachineConfig的父类 */ dbStateMachineConfig.setResources(new PathMatchingResourcePatternResolver().getResources("classpath*:statelang/*.json"));//json文件 dbStateMachineConfig.setEnableAsync(true); dbStateMachineConfig.setApplicationId("order-server"); dbStateMachineConfig.setTxServiceGroup("my_test_tx_group"); return dbStateMachineConfig; } @Bean public ProcessCtrlStateMachineEngine stateMachineEngine(DbStateMachineConfig dbStateMachineConfig){ ProcessCtrlStateMachineEngine stateMachineEngine = new ProcessCtrlStateMachineEngine(); stateMachineEngine.setStateMachineConfig(dbStateMachineConfig); return stateMachineEngine; } @Bean public StateMachineEngineHolder stateMachineEngineHolder(ProcessCtrlStateMachineEngine stateMachineEngine){ StateMachineEngineHolder stateMachineEngineHolder = new StateMachineEngineHolder(); stateMachineEngineHolder.setStateMachineEngine(stateMachineEngine); return stateMachineEngineHolder; } }可以看到，我们在DbStateMachineConfig中配置了状态机的json文件，同时配置了applicationId和txServiceGroup。在DbStateMachineConfig初始化的时候，子类DefaultStateMachineConfig的init的方法会把json文件解析成状态机，并注册。
注册的过程中往seata_state_machine_def这张表里插入了1条记录，表里的content字段保存了我们的JOSON文件内容，其他字段值数据如下图：
附:根据前面的JSON文件，我们debug跟踪到的StateMachineImpl的内容如下：
id = null tenantId = null appName = "SEATA" name = "buyGoodsOnline" comment = "buy a goods on line, add order, deduct account, deduct storage " version = "0.0.1" startState = "SaveOrder" status = {StateMachine$Status@9135} "AC" recoverStrategy = null isPersist = true type = "STATE_LANG" content = null gmtCreate = null states = {LinkedHashMap@9137} size = 11 "SaveOrder" -> {ServiceTaskStateImpl@9153} "ChoiceAccountState" -> {ChoiceStateImpl@9155} "ReduceAccount" -> {ServiceTaskStateImpl@9157} "ChoiceStorageState" -> {ChoiceStateImpl@9159} "ReduceStorage" -> {ServiceTaskStateImpl@9161} "DeleteOrder" -> {ServiceTaskStateImpl@9163} "CompensateReduceAccount" -> {ServiceTaskStateImpl@9165} "CompensateReduceStorage" -> {ServiceTaskStateImpl@9167} "CompensationTrigger" -> {CompensationTriggerStateImpl@9169} "Succeed" -> {SucceedEndStateImpl@9171} "Fail" -> {FailEndStateImpl@9173}启动状态机
在第一节创建订单的代码中，startWithBusinessKey方法进行了整个事务的启动，这个方法还有一个异步模式startWithBusinessKeyAsync，这里我们只分析同步模式，源代码如下：
public StateMachineInstance startWithBusinessKey(String stateMachineName, String tenantId, String businessKey, Map<String, Object> startParams) throws EngineExecutionException { return startInternal(stateMachineName, tenantId, businessKey, startParams, false, null); } private StateMachineInstance startInternal(String stateMachineName, String tenantId, String businessKey, Map<String, Object> startParams, boolean async, AsyncCallback callback) throws EngineExecutionException { //省略部分源代码 //创建一个状态机实例 //默认值tenantId="000001" StateMachineInstance instance = createMachineInstance(stateMachineName, tenantId, businessKey, startParams); /** * ProcessType.STATE_LANG这个枚举只有一个元素 * OPERATION_NAME_START = "start" * callback是null * getStateMachineConfig()返回DbStateMachineConfig */ ProcessContextBuilder contextBuilder = ProcessContextBuilder.create().withProcessType(ProcessType.STATE_LANG) .withOperationName(DomainConstants.OPERATION_NAME_START).withAsyncCallback(callback).withInstruction( new StateInstruction(stateMachineName, tenantId)).withStateMachineInstance(instance) .withStateMachineConfig(getStateMachineConfig()).withStateMachineEngine(this); Map<String, Object> contextVariables; if (startParams != null) { contextVariables = new ConcurrentHashMap<>(startParams.size()); nullSafeCopy(startParams, contextVariables); } else { contextVariables = new ConcurrentHashMap<>(); } instance.setContext(contextVariables);//把启动参数赋值给状态机实例的context //给ProcessContextImpl的variables加参数 contextBuilder.withStateMachineContextVariables(contextVariables); contextBuilder.withIsAsyncExecution(async); //上面定义的建造者创建一个ProcessContextImpl ProcessContext processContext = contextBuilder.build(); //这个条件是true if (instance.getStateMachine().isPersist() && stateMachineConfig.getStateLogStore() != null) { //记录状态机开始状态 stateMachineConfig.getStateLogStore().recordStateMachineStarted(instance, processContext); } if (StringUtils.isEmpty(instance.getId())) { instance.setId( stateMachineConfig.getSeqGenerator().generate(DomainConstants.SEQ_ENTITY_STATE_MACHINE_INST)); } if (async) { stateMachineConfig.getAsyncProcessCtrlEventPublisher().publish(processContext); } else { //发送消息到EventBus，这里的消费者是ProcessCtrlEventConsumer，在DefaultStateMachineConfig初始化时设置 stateMachineConfig.getProcessCtrlEventPublisher().publish(processContext); } return instance; }上面的代码中我们可以看出，启动状态记得时候主要做了2件事情，一个是记录状态机开始的状态，一个是发送消息到EventBus，下面我们详细看一下这2个过程。
开启全局事务
上面的代码分析中，有一个记录状态机开始状态的代码，如下：
stateMachineConfig.getStateLogStore().recordStateMachineStarted(instance, processContext);
这里调用了类DbAndReportTcStateLogStore的recordStateMachineStarted方法，我们来看一下，代码如下：
public void recordStateMachineStarted(StateMachineInstance machineInstance, ProcessContext context) { if (machineInstance != null) { //if parentId is not null, machineInstance is a SubStateMachine, do not start a new global transaction, //use parent transaction instead. String parentId = machineInstance.getParentId(); if (StringUtils.hasLength(parentId)) { if (StringUtils.isEmpty(machineInstance.getId())) { machineInstance.setId(parentId); } } else { //走这个分支，因为没有配置子状态机 /** * 这里的beginTransaction就是开启全局事务， * 这里是调用TC开启全局事务 */ beginTransaction(machineInstance, context); } if (StringUtils.isEmpty(machineInstance.getId()) && seqGenerator != null) { machineInstance.setId(seqGenerator.generate(DomainConstants.SEQ_ENTITY_STATE_MACHINE_INST)); } // save to db //dbType = "MySQL" machineInstance.setSerializedStartParams(paramsSerializer.serialize(machineInstance.getStartParams())); executeUpdate(stateLogStoreSqls.getRecordStateMachineStartedSql(dbType), STATE_MACHINE_INSTANCE_TO_STATEMENT_FOR_INSERT, machineInstance); } }上面executeUpdate方法在子类AbstractStore,debug一下executeUpdate这个方法可以看到，这里执行的sql如下：
INSERT INTO seata_state_machine_inst (id, machine_id, tenant_id, parent_id, gmt_started, business_key, start_params, is_running, status, gmt_updated) VALUES ('192.168.59.146:8091:65853497147990016', '06a098cab53241ca7ed09433342e9f07', '000001', null, '2020-10-31 17:18:24.773', '1604135904773', '{"@type":"java.util.HashMap","money":50.,"productId":1L,"_business_key_":"1604135904773","businessKey":"1604135904773", "count":1,"mockReduceAccountFail":"true","userId":1L,"order":{"@type":"io.seata.sample.entity.Order","count":1,"payAmount":50, "productId":1,"userId":1}}', 1, 'RU', '2020-10-31 17:18:24.773')可以看到，这个全局事务记录在了表seata_state_machine_inst，记录的是我们启动状态机的参数，status记录的状态是"RU"也就是RUNNING。
分支事务处理
上一节我们提到，启动状态机后，向EventBus发了一条消息，这个消息的消费者是ProcessCtrlEventConsumer，我们看一下这个类的代码：
public class ProcessCtrlEventConsumer implements EventConsumer<ProcessContext> { private ProcessController processController; @Override public void process(ProcessContext event) throws FrameworkException { //这里的processController是ProcessControllerImpl processController.process(event); } @Override public boolean accept(Class<ProcessContext> clazz) { return ProcessContext.class.isAssignableFrom(clazz); } public void setProcessController(ProcessController processController) { this.processController = processController; } }ProcessControllerImpl类的process方法有2个处理逻辑，process和route，代码如下：
public void process(ProcessContext context) throws FrameworkException { try { //这里的businessProcessor是CustomizeBusinessProcessor businessProcessor.process(context); businessProcessor.route(context); } catch (FrameworkException fex) { throw fex; } catch (Exception ex) { LOGGER.error("Unknown exception occurred, context = {}", context, ex); throw new FrameworkException(ex, "Unknown exception occurred", FrameworkErrorCode.UnknownAppError); } }这里的处理逻辑有些复杂，先上一张UML类图，跟着这张图，可以捋清楚代码的调用逻辑：
我们先来看一下CustomizeBusinessProcessor中的process方法：
public void process(ProcessContext context) throws FrameworkException { /** *processType = {ProcessType@10310} "STATE_LANG" *code = "STATE_LANG" *message = "SEATA State Language" *name = "STATE_LANG" *ordinal = 0 */ ProcessType processType = matchProcessType(context); if (processType == null) { if (LOGGER.isWarnEnabled()) { LOGGER.warn("Process type not found, context= {}", context); } throw new FrameworkException(FrameworkErrorCode.ProcessTypeNotFound); } ProcessHandler processor = processHandlers.get(processType.getCode()); if (processor == null) { LOGGER.error("Cannot find process handler by type {}, context= {}", processType.getCode(), context); throw new FrameworkException(FrameworkErrorCode.ProcessHandlerNotFound); } //这里的是StateMachineProcessHandler processor.process(context); }这里的代码不好理解，我们分四步来研究。
第一步，我们看一下StateMachineProcessHandler类中process方法，这个方法代理了ServiceTaskStateHandler的process方法，代码如下：
public void process(ProcessContext context) throws FrameworkException { /** * instruction = {StateInstruction@11057} * stateName = null * stateMachineName = "buyGoodsOnline" * tenantId = "000001" * end = false * temporaryState = null */ StateInstruction instruction = context.getInstruction(StateInstruction.class); //这里的state实现类是ServiceTaskStateImpl State state = instruction.getState(context); String stateType = state.getType(); //这里stateHandler实现类是ServiceTaskStateHandler StateHandler stateHandler = stateHandlers.get(stateType); List<StateHandlerInterceptor> interceptors = null; if (stateHandler instanceof InterceptableStateHandler) { //list上有1个元素ServiceTaskHandlerInterceptor interceptors = ((InterceptableStateHandler)stateHandler).getInterceptors(); } List<StateHandlerInterceptor> executedInterceptors = null; Exception exception = null; try { if (interceptors != null && interceptors.size() > 0) { executedInterceptors = new ArrayList<>(interceptors.size()); for (StateHandlerInterceptor interceptor : interceptors) { executedInterceptors.add(interceptor); interceptor.preProcess(context); } } stateHandler.process(context); } catch (Exception e) { exception = e; throw e; } finally { if (executedInterceptors != null && executedInterceptors.size() > 0) { for (int i = executedInterceptors.size() - 1; i >= 0; i--) { StateHandlerInterceptor interceptor = executedInterceptors.get(i); interceptor.postProcess(context, exception); } } } }从这个方法我们看到，代理对stateHandler.process加入了前置和后置增强，增强类是ServiceTaskHandlerInterceptor，前置后置增强分别调用了interceptor的preProcess和postProcess。
第二步，我们来看一下增强逻辑。ServiceTaskHandlerInterceptor的preProcess和postProcess方法，代码如下：
public class ServiceTaskHandlerInterceptor implements StateHandlerInterceptor { //省略部分代码 @Override public void preProcess(ProcessContext context) throws EngineExecutionException { StateInstruction instruction = context.getInstruction(StateInstruction.class); StateMachineInstance stateMachineInstance = (StateMachineInstance)context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_INST); StateMachineConfig stateMachineConfig = (StateMachineConfig)context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_CONFIG); //如果超时,修改状态机状态为FA if (EngineUtils.isTimeout(stateMachineInstance.getGmtUpdated(), stateMachineConfig.getTransOperationTimeout())) { String message = "Saga Transaction [stateMachineInstanceId:" + stateMachineInstance.getId() + "] has timed out, stop execution now."; EngineUtils.failStateMachine(context, exception); throw exception; } StateInstanceImpl stateInstance = new StateInstanceImpl(); Map<String, Object> contextVariables = (Map<String, Object>)context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_CONTEXT); ServiceTaskStateImpl state = (ServiceTaskStateImpl)instruction.getState(context); List<Object> serviceInputParams = null; Object isForCompensation = state.isForCompensation(); if (isForCompensation != null && (Boolean)isForCompensation) { CompensationHolder compensationHolder = CompensationHolder.getCurrent(context, true); StateInstance stateToBeCompensated = compensationHolder.getStatesNeedCompensation().get(state.getName()); if (stateToBeCompensated != null) { stateToBeCompensated.setCompensationState(stateInstance); stateInstance.setStateIdCompensatedFor(stateToBeCompensated.getId()); } else { LOGGER.error("Compensation State[{}] has no state to compensate, maybe this is a bug.", state.getName()); } //加入补偿集合 CompensationHolder.getCurrent(context, true).addForCompensationState(stateInstance.getName(), stateInstance); } //省略部分代码 stateInstance.setInputParams(serviceInputParams); if (stateMachineInstance.getStateMachine().isPersist() && state.isPersist() && stateMachineConfig.getStateLogStore() != null) { try { //记录一个分支事务的状态RU到数据库 /** *INSERT INTO seata_state_inst (id, machine_inst_id, name, type, gmt_started, service_name, service_method, service_type, is_for_update, input_params, status, business_key, state_id_compensated_for, state_id_retried_for) *VALUES ('4fe5f602452c84ba5e88fd2ee9c13b35', '192.168.59.146:8091:65853497147990016', 'SaveOrder', 'ServiceTask', '2020-10-31 17:18:40.84', 'orderSave', *'saveOrder', null, 1, '["1604135904773",{"@type":"io.seata.sample.entity.Order","count":1,"payAmount":50,"productId":1,"userId":1}]', 'RU', null, null, null) */ stateMachineConfig.getStateLogStore().recordStateStarted(stateInstance, context); } } //省略部分代码 stateMachineInstance.putStateInstance(stateInstance.getId(), stateInstance);//放入StateMachineInstanceImpl的stateMap用于重试或交易补偿 ((HierarchicalProcessContext)context).setVariableLocally(DomainConstants.VAR_NAME_STATE_INST, stateInstance);//记录状态后面传给TaskStateRouter判断全局事务结束 } @Override public void postProcess(ProcessContext context, Exception exp) throws EngineExecutionException { StateInstruction instruction = context.getInstruction(StateInstruction.class); ServiceTaskStateImpl state = (ServiceTaskStateImpl)instruction.getState(context); StateMachineInstance stateMachineInstance = (StateMachineInstance)context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_INST); StateInstance stateInstance = (StateInstance)context.getVariable(DomainConstants.VAR_NAME_STATE_INST); if (stateInstance == null || !stateMachineInstance.isRunning()) { LOGGER.warn("StateMachineInstance[id:" + stateMachineInstance.getId() + "] is end. stop running"); return; } StateMachineConfig stateMachineConfig = (StateMachineConfig)context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_CONFIG); if (exp == null) { exp = (Exception)context.getVariable(DomainConstants.VAR_NAME_CURRENT_EXCEPTION); } stateInstance.setException(exp); //设置事务状态 decideExecutionStatus(context, stateInstance, state, exp); //省略部分代码 Map<String, Object> contextVariables = (Map<String, Object>)context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_CONTEXT); //省略部分代码 context.removeVariable(DomainConstants.VAR_NAME_OUTPUT_PARAMS); context.removeVariable(DomainConstants.VAR_NAME_INPUT_PARAMS); stateInstance.setGmtEnd(new Date()); if (stateMachineInstance.getStateMachine().isPersist() && state.isPersist() && stateMachineConfig.getStateLogStore() != null) { //更新分支事务的状态为成功 /** * UPDATE seata_state_inst SET gmt_end = '2020-10-31 17:18:49.919', excep = null, status = 'SU', * output_params = 'true' WHERE id = '4fe5f602452c84ba5e88fd2ee9c13b35' AND * machine_inst_id = '192.168.59.146:8091:65853497147990016' */ stateMachineConfig.getStateLogStore().recordStateFinished(stateInstance, context); } //省略部分代码 } }从这个代码我们能看到，分支事务执行前，封装了一个StateInstanceImpl赋值给了ProcessContext，分支事务执行后，对这个StateInstanceImpl进行了修改，这个StateInstanceImpl有3个作用：
传入StateMachineInstanceImpl的stateMap用于重试或交易补偿
记录了分支事务的执行情况，同时支持持久化到seata_state_inst表
传入TaskStateRouter用作判断全局事务结束
第三步，我们看一下被代理的方法stateHandler.process(context)，正常执行逻辑中stateHandler的实现类是ServiceTaskStateHandler，代码如下：
public void process(ProcessContext context) throws EngineExecutionException { StateInstruction instruction = context.getInstruction(StateInstruction.class); ServiceTaskStateImpl state = (ServiceTaskStateImpl) instruction.getState(context); StateInstance stateInstance = (StateInstance) context.getVariable(DomainConstants.VAR_NAME_STATE_INST); Object result; try { /** * 这里的input是我们在JSON中定义的，比如orderSave这个ServiceTask，input如下： * 0 = "1608714480316" * 1 = {Order@11271} "Order(id=null, userId=1, productId=1, count=1, payAmount=50, status=null)" * JSON中定义如下： * "Input": [ * "$.[businessKey]", * "$.[order]" * ] */ List<Object> input = (List<Object>) context.getVariable(DomainConstants.VAR_NAME_INPUT_PARAMS); //Set the current task execution status to RU (Running) stateInstance.setStatus(ExecutionStatus.RU);//设置状态 if (state instanceof CompensateSubStateMachineState) { //省略子状态机的研究 } else { StateMachineConfig stateMachineConfig = (StateMachineConfig) context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_CONFIG); //这里的state.getServiceType是springBean ServiceInvoker serviceInvoker = stateMachineConfig.getServiceInvokerManager().getServiceInvoker( state.getServiceType()); if (serviceInvoker == null) { throw new EngineExecutionException("No such ServiceInvoker[" + state.getServiceType() + "]", FrameworkErrorCode.ObjectNotExists); } if (serviceInvoker instanceof ApplicationContextAware) { ((ApplicationContextAware) serviceInvoker).setApplicationContext( stateMachineConfig.getApplicationContext()); } //这里触发了我们在JSON中定义ServiceTask中方法，比如orderSave中的saveOrder方法 result = serviceInvoker.invoke(state, input.toArray()); } if (LOGGER.isDebugEnabled()) { LOGGER.debug("<<<<<<<<<<<<<<<<<<<<<< State[{}], ServiceName[{}], Method[{}] Execute finish. result: {}", state.getName(), serviceName, methodName, result); } //省略部分代码 } //省略异常处理代码 }可以看到，process这个方法是一个核心的业务处理，它用发射触发了JSON中定义ServiceTask的方法，并且根据状态触发了Next对象，即流程中的下一个ServiceTask。
第四步，我们再看一下CustomizeBusinessProcessor的route方法，代码如下：
public void route(ProcessContext context) throws FrameworkException { //code = "STATE_LANG" //message = "SEATA State Language" //name = "STATE_LANG" //ordinal = 0 ProcessType processType = matchProcessType(context); RouterHandler router = routerHandlers.get(processType.getCode()); //DefaultRouterHandler的route方法 router.route(context); }我们看一下DefaultRouterHandler的route方法，代码如下：
public void route(ProcessContext context) throws FrameworkException { try { ProcessType processType = matchProcessType(context); //这里的processRouter是StateMachineProcessRouter ProcessRouter processRouter = processRouters.get(processType.getCode()); Instruction instruction = processRouter.route(context); if (instruction == null) { LOGGER.info("route instruction is null, process end"); } else { context.setInstruction(instruction); eventPublisher.publish(context); } } catch (FrameworkException e) { throw e; } catch (Exception ex) { throw new FrameworkException(ex, ex.getMessage(), FrameworkErrorCode.UnknownAppError); } }看一下StateMachineProcessRouter的route方法，这里也是用了代理模式，代码如下：
public Instruction route(ProcessContext context) throws FrameworkException { StateInstruction stateInstruction = context.getInstruction(StateInstruction.class); State state; if (stateInstruction.getTemporaryState() != null) { state = stateInstruction.getTemporaryState(); stateInstruction.setTemporaryState(null); } else { //走这个分支 StateMachineConfig stateMachineConfig = (StateMachineConfig)context.getVariable( DomainConstants.VAR_NAME_STATEMACHINE_CONFIG); StateMachine stateMachine = stateMachineConfig.getStateMachineRepository().getStateMachine( stateInstruction.getStateMachineName(), stateInstruction.getTenantId()); state = stateMachine.getStates().get(stateInstruction.getStateName()); } String stateType = state.getType(); StateRouter router = stateRouters.get(stateType); Instruction instruction = null; List<StateRouterInterceptor> interceptors = null; if (router instanceof InterceptableStateRouter) { //这里只有EndStateRouter interceptors = ((InterceptableStateRouter)router).getInterceptors();//EndStateRouterInterceptor } List<StateRouterInterceptor> executedInterceptors = null; Exception exception = null; try { //前置增量实现方法是空，这里省略代码 instruction = router.route(context, state); } catch (Exception e) { exception = e; throw e; } finally { if (executedInterceptors != null && executedInterceptors.size() > 0) { for (int i = executedInterceptors.size() - 1; i >= 0; i--) { StateRouterInterceptor interceptor = executedInterceptors.get(i); interceptor.postRoute(context, state, instruction, exception);//结束状态机 } } //if 'Succeed' or 'Fail' State did not configured, we must end the state machine if (instruction == null && !stateInstruction.isEnd()) { EngineUtils.endStateMachine(context); } } return instruction; }这里的代理只实现了一个后置增强，做的事情就是结束状态机。
下面我们来看一下StateRouter，UML类图如下：
从UML类图我们看到，除了EndStateRouter，只有一个TaskStateRouter了。而EndStateRouter并没有做什么事情，因为关闭状态机的逻辑已经由代理做了。这里我们看一下TaskStateRouter，代码如下：
public Instruction route(ProcessContext context, State state) throws EngineExecutionException { StateInstruction stateInstruction = context.getInstruction(StateInstruction.class); if (stateInstruction.isEnd()) { //如果已经结束，直接返回 //省略代码 } //The current CompensationTriggerState can mark the compensation process is started and perform compensation // route processing. State compensationTriggerState = (State)context.getVariable( DomainConstants.VAR_NAME_CURRENT_COMPEN_TRIGGER_STATE); if (compensationTriggerState != null) { //加入补偿集合进行补偿并返回 return compensateRoute(context, compensationTriggerState); } //There is an exception route, indicating that an exception is thrown, and the exception route is prioritized. String next = (String)context.getVariable(DomainConstants.VAR_NAME_CURRENT_EXCEPTION_ROUTE); if (StringUtils.hasLength(next)) { context.removeVariable(DomainConstants.VAR_NAME_CURRENT_EXCEPTION_ROUTE); } else { next = state.getNext(); } //If next is empty, the state selected by the Choice state was taken. if (!StringUtils.hasLength(next) && context.hasVariable(DomainConstants.VAR_NAME_CURRENT_CHOICE)) { next = (String)context.getVariable(DomainConstants.VAR_NAME_CURRENT_CHOICE); context.removeVariable(DomainConstants.VAR_NAME_CURRENT_CHOICE); } //从当前context中取不出下一个节点了，直接返回 if (!StringUtils.hasLength(next)) { return null; } StateMachine stateMachine = state.getStateMachine(); State nextState = stateMachine.getState(next); if (nextState == null) { throw new EngineExecutionException("Next state[" + next + "] is not exits", FrameworkErrorCode.ObjectNotExists); } //获取到下一个要流转的状态并且赋值给stateInstruction stateInstruction.setStateName(next); return stateInstruction; }可以看到，route的作用是帮状态机确定下一个流程节点，然后放入到当前的context中的stateInstruction。
到这里，我们就分析完成了状态机的原理，ProcessControllerImpl类中。
需要注意的是，这里获取到下一个节点后，并没有直接处理，而是使用观察者模式，先发送到EventBus，等待观察者来处理，循环往复，直到EndStateRouter结束状态机。
这里观察者模式的Event是ProcessContext，里面包含了Instruction，而Instruction里面包含了State，这个State里面就决定了下一个处理的节点直到结束。UML类图如下：
总结
seata中间件中的saga模式使用比较广泛，但是代码还是比较复杂的。我从下面几个方面进行了梳理：
我们定义的json文件加载到了类StateMachineImpl中。
启动状态机，我们也就启动了全局事务，这个普通模式启动全局事务是一样的，都会向TC发送消息。
处理状态机状态和控制状态流转的入口类在ProcessControllerImpl，从process方法可以跟代码。
ProcessControllerImpl调用CustomizeBusinessProcessor的process处理当前状态，然后调用route方法获取到下一个节点并发送到EventBus。
saga模式额外引入了3张表，我们也可以根据跟全局事务和分支事务相关的2张表来跟踪代码，我之前给出的demo，如果事务成功，这2张表的写sql按照状态机执行顺序给出一个成功sql，代码如下：
INSERT INTO seata_state_machine_inst (id, machine_id, tenant_id, parent_id, gmt_started, business_key, start_params, is_running, status, gmt_updated) VALUES ('192.168.59.146:8091:65853497147990016', '06a098cab53241ca7ed09433342e9f07', '000001', null, '2020-10-31 17:18:24.773', '1604135904773', '{"@type":"java.util.HashMap","money":50.,"productId":1L,"_business_key_":"1604135904773","businessKey":"1604135904773",\"count\":1,\"mockreduceaccountfail\":\"true\","userId":1L,"order":{"@type":"io.seata.sample.entity.Order","count":1,"payAmount":50,"productId":1,"userId":1}}', 1, 'RU', '2020-10-31 17:18:24.773') INSERT INTO seata_state_inst (id, machine_inst_id, name, type, gmt_started, service_name, service_method, service_type, is_for_update, input_params, status, business_key, state_id_compensated_for, state_id_retried_for) VALUES ('4fe5f602452c84ba5e88fd2ee9c13b35', '192.168.59.146:8091:65853497147990016', 'SaveOrder', 'ServiceTask', '2020-10-31 17:18:40.84', 'orderSave', 'saveOrder', null, 1, '["1604135904773",{"@type":"io.seata.sample.entity.Order","count":1,"payAmount":50,"productId":1,"userId":1}]', 'RU', null, null, null) UPDATE seata_state_inst SET gmt_end = '2020-10-31 17:18:49.919', excep = null, status = 'SU', output_params = 'true' WHERE id = '4fe5f602452c84ba5e88fd2ee9c13b35' AND machine_inst_id = '192.168.59.146:8091:65853497147990016' INSERT INTO seata_state_inst (id, machine_inst_id, name, type, gmt_started, service_name, service_method, service_type, is_for_update, input_params, status, business_key, state_id_compensated_for, state_id_retried_for) VALUES ('8371235cb2c66c8626e148f66123d3b4', '192.168.59.146:8091:65853497147990016', 'ReduceAccount', 'ServiceTask', '2020-10-31 17:19:00.441', 'accountService', 'decrease', null, 1, '["1604135904773",1L,50.,{"@type":"java.util.LinkedHashMap","throwException":"true"}]', 'RU', null, null, null) UPDATE seata_state_inst SET gmt_end = '2020-10-31 17:19:09.593', excep = null, status = 'SU', output_params = 'true' WHERE id = '8371235cb2c66c8626e148f66123d3b4' AND machine_inst_id = '192.168.59.146:8091:65853497147990016' INSERT INTO seata_state_inst (id, machine_inst_id, name, type, gmt_started, service_name, service_method, service_type, is_for_update, input_params, status, business_key, state_id_compensated_for, state_id_retried_for) VALUES ('e70a49f1eac72f929085f4e82c2b4de2', '192.168.59.146:8091:65853497147990016', 'ReduceStorage', 'ServiceTask', '2020-10-31 17:19:18.494', 'storageService', 'decrease', null, 1, '["1604135904773",1L,1,{"@type":"java.util.LinkedHashMap"}]', 'RU', null, null, null) UPDATE seata_state_inst SET gmt_end = '2020-10-31 17:19:26.613', excep = null, status = 'SU', output_params = 'true' WHERE id = 'e70a49f1eac72f929085f4e82c2b4de2' AND machine_inst_id = '192.168.59.146:8091:65853497147990016' UPDATE seata_state_machine_inst SET gmt_end = '2020-10-31 17:19:33.581', excep = null, end_params = '{"@type":"java.util.HashMap","productId":1L,"count":1,"ReduceAccountResult":true,"mockReduceAccountFail":"true","userId":1L,"money":50.,"SaveOrderResult":true,"_business_key_":"1604135904773","businessKey":"1604135904773","ReduceStorageResult":true,"order":{"@type":"io.seata.sample.entity.Order","count":1,"id":60,"payAmount":50,"productId":1,"userId":1}}',status = 'SU', compensation_status = null, is_running = 0, gmt_updated = '2020-10-31 17:19:33.582' WHERE id = '192.168.59.146:8091:65853497147990016' and gmt_updated = '2020-10-31 17:18:24.773'到此，相信大家对“Saga模式源码方法教程”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
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