Package oracle.dbtools.plugin.api.conf

Services for defining and introspecting Configuration Settings

About Configuration Settings

Each plugin may contribute zero or more ConfigurationSetting values. By declaring discoverable ConfigurationSetting values a plugin enables two things:

  • The plugin's settings may be managed in the same manner across all plugins. Configuration Tooling can operate on the plugin's settings automatically
  • The plugin can inject the setting's value directly into an javax.inject.Inject injection site. This reduces coupling to the Plugin API, making it easier to re-use or share code in the plugin in other code bases and it also facilitates easier unit testing. Unit tests can just pass the the required values directly to the class under test, rather than having to pass values via the Configuration API

Declaring a Configuration Setting

Each setting is uniquely defined by it's name. It must have a data-type and may also have the following optional attributes:
  • A default value, used when no explicit value for the settings is provided in the Configuration
  • A flag indicating if the value is sensitive (such as a password) and should be stored/accessed securely
  • A flag indicating if the setting is global and applies across the entire application, rather than being configurable per request

Best practice is to define a constant for the setting name and use that constant rather than a literal string. The ConfigurationSetting should be defined as a final static constant. The field must be annotated with javax.inject.Named to indicate the unique name of the setting.

The field or it's enclosing type must be annotated with Provides so that the field is discoverable.

Supported data types

ConfigurationSetting data-types must be one of the following:
  • String - A textual value
  • Integer - An integer value
  • Long - A large integer value
  • Boolean - A boolean value. It is recommended that the default value for a Boolean setting is always Boolean.FALSE
  • A subclass of Enum - Where the value of is one of the case insensitive name of enum value names
  • TimeDuration - A value representing a duration

Examples

Undocumented Integer Setting

 
 public interface PluginSettings {
        static final String SETTING_FOO = "my.plugin.setting.foo";
 }
 
 @Provides
 class PluginImpl {
        @Named(PluginSettings.SETTING_FOO)
        static final ConfigurationSetting FOO = ConfigurationSetting.setting(10);
 }

Documented Enum Setting

 
 public interface PluginSettings {
        static final String ACCESS_MODE_SETTING = "my.plugin.accessMode";
 }
 
 @Provides
 class PluginImpl {
        @Named(PluginSettings.ACCESS_MODE_SETTING)
        @ConfigurationSetting.Description(@TranslatableDescription(type = MyPluginMessages.class, id = MyPluginMessages.ACCESS_MODE_DESCRIPTION))
        static final ConfigurationSetting ACCESS_MODE = ConfigurationSetting.setting(java.nio.AccessMode.class,
                        java.nio.AccessMode.READ);
 }

Injecting Configuration Settings

When a ConfigurationSetting is declared as outlined above, the Dependency Injection runtime is able to map each setting to a concrete value derived from the Configuration instance applicable to the current scope. Thus instead of invoking Configuration.get(String) (which is strongly discouraged) a plugin service can just declare a dependency on the configuration setting value via an appropriately typed and javax.inject.Named parameter in it's constructor

For example to inject the my.plugin.setting.foo configuration setting value into some service, one would do: 

 @Provides
 class MyPluginService implements SomeService {
   @Inject
   MyPluginService(final @Named(PluginSettings.FOO_SETTING) int foo) {
    ...
   }
 }

Boxing and Unboxing of Primitive Types

For ease of use, injection sites may use primitive types where applicable.

  • Settings of type Integer can be injected as int
  • Settings of type Long can be injected as long
  • Settings of type Boolean can be injected as boolean

Note in each case if no default value is specified for the setting and the Configuration also lacks a value for the setting then a runtime error will occur during creation of the service and likely lead to the application not starting.

Author:
cdivilly