flowable ContentEngine和ContentEngineConfiguration的关系

一、CommandExecutor

ContentEngineConfiguration继承自 AbstractEngineConfiguration。

在 AbstractEngineConfiguration 中包含一个CommandExecutor 属性。

protected CommandExecutor commandExecutor;

二、ContentManagementService和ContentService

ContentEngineConfiguration中包含两个属性：

    protected ContentManagementService contentManagementService = new ContentManagementServiceImpl();

    protected ContentService contentService = new ContentServiceImpl();

三、创建ContentEngine

ContentEngine是通过调用ContentEngineConfiguration实例的buildContentEngine()完成创建的。

 public ContentEngine buildContentEngine() {
        init();
        return new ContentEngineImpl(this);
    }

1、传递CommandExecutor

在调用ContentEngineConfiguration的buildContentEngine()方法时，在 AbstractEngineConfiguration 中包含的CommandExecutor 属性被赋值给ServiceImpl。代码如下：

 protected void initServices() {
        initService(contentManagementService);
        initService(contentService);
    }

    protected void initService(Object service) {
        if (service instanceof ServiceImpl) {
            ((ServiceImpl) service).setCommandExecutor(commandExecutor);
        }
    }

ServiceImpl是ContentService和ContentManagementService的父类，包含一个CommandExecutor 属性。（见下图）

至此，ContentEngineConfiguration 初始化了ContentService和ContentManagementService，并把父类中的CommandExecutor传递给了这两个类的实例。

2、构建ContentEngine

ContentEngineConfiguration被当作参数传递给ContentEngineImpl的构造方法。

 public ContentEngine buildContentEngine() {
        init();
        return new ContentEngineImpl(this);
    }

ContentEngineImpl通过ContentEngineConfiguration得到ConentService和ContentManagementService，并对外提供。

public ContentEngineImpl(ContentEngineConfiguration engineConfiguration) {
        this.engineConfiguration = engineConfiguration;
        this.name = engineConfiguration.getEngineName();
        this.managementService = engineConfiguration.getContentManagementService();
        this.contentService = engineConfiguration.getContentService();
        ...
 }

ContentEngine 提供的服务最终的执行者是ContentService和ContentManagementService的父类 ServiceImpl；

而 ServiceImpl的执行器是由 AbstractEngineConfiguration提供的。