flowable ProcessEngine和ProcessEngineConfiguration

ProcessEngine是流程引擎，ProcessEngineConfiguration与前面四个引擎配置有些不同。

ProcessEngineConfiguration增加了邮件服务和httpClient的封装。

一、实例化

ProcessEngineConfiguration 提供了7个公共的静态方法用于实例化。

   public static ProcessEngineConfiguration createStandaloneProcessEngineConfiguration() {        return new StandaloneProcessEngineConfiguration();    }    public static ProcessEngineConfiguration createStandaloneInMemProcessEngineConfiguration() {        return new StandaloneInMemProcessEngineConfiguration();    }

二、创建ProcessEngine

创建ProcessEngine的方法是在ProcessEngineConfiguration的子类 ProcessEngineConfigurationImpl中提供的。

@Override    public ProcessEngine buildProcessEngine() {        init();        ProcessEngineImpl processEngine = new ProcessEngineImpl(this);...        return processEngine;    }

三、初始化服务

创建引擎过程调用init()方法时，初始化服务。

public void init() {...initServices();...}public void initServices() {        initService(repositoryService);        initService(runtimeService);        initService(historyService);        initService(identityService);        initService(taskService);        initService(formService);        initService(managementService);        initService(dynamicBpmnService);    }    public void initService(Object service) {        if (service instanceof ServiceImpl) {            ((ServiceImpl) service).setCommandExecutor(commandExecutor);        }    }

这些服务定义在 ProcessEngineConfigurationImpl 中：

  protected RepositoryService repositoryService = new RepositoryServiceImpl();    protected RuntimeService runtimeService = new RuntimeServiceImpl();    protected HistoryService historyService = new HistoryServiceImpl(this);    protected IdentityService identityService = new IdentityServiceImpl(this);    protected TaskService taskService = new TaskServiceImpl(this);    protected FormService formService = new FormServiceImpl();    protected ManagementService managementService = new ManagementServiceImpl();    protected DynamicBpmnService dynamicBpmnService = new DynamicBpmnServiceImpl(this);

初始化使AbstractEngineConfiguration的 CommandExecutor传递到这些服务的父类 ServiceImpl 中。

这些服务随着 processEngineConfigurationImpl实例传递给 processEngin实例。