When Drogon runs the run() interface, it instantiates each plugin one by one according to the configuration file and calls the interface of them.

Plugin configuration is done through the configuration file, for example:

  • dependencies: Is a list of names of other plugins that the plugin depends on. The framework creates and initializes all plugins in a specific order. Prioritize the creation and initialization of plugins that are dependent by others. At the end of the program, plugins are closed and destroyed in reverse order. Please note that circular dependencies in plugins are forbidden. Drogon will report an error and exit the program if it detects a circular dependency. If the item is commented out, the list of dependencies is empty.
  • config: is the json object used to initialize the plugin, the object is passed as an input parameter to the plugin’s initAndStart() interface. If the item is commented out, the json object passed to the initAndStart interface is an empty object;

User-defined plugins must inherit from the drogon::Plugin class template, and the template parameter is the plugin type, such as the following definition:

  1. class DataDictionary : public drogon::Plugin<DataDictionary>
  3.     virtual void initAndStart(const Json::Value &config) override;
  4.     virtual void shutdown() override;
  6. };

One can create source files of plugin by drogon_ctl command:

    Or

    Obviously, the first method is more convenient. For example, the DataDictionary plugin mentioned above can be obtained like this:

    1. auto *pluginPtr=app().getPlugin<DataDictionary>();

    All plugins are initialized in the run() interface of the framework and are destroyed when the application exits. Therefore, the plugin’s lifecycle is almost identical to the application, which is why the getPlugin() interface does not need to return a smart pointer.

    10 Configuration File