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Accessing or Creating a certain Configuration

For using Microprofile-Config in a programmatic way the ConfigProvider class is the central point to access a configuration. It allows access to different configurations (represented by a Config instance) based on the application in which it is used. The ConfigProvider internally delegates through to the ConfigProviderResolver which contains more low-level functionality.

There are 4 different ways to create a Config instance:

  • In CDI managed components, a user can use @Inject to access the current application configuration. The default and the auto discovered ConfigSources will be gathered to form a configuration. The default and the auto discovered Converters will be gathered to form a configuration. Injected instance of Config should behave the same as the one retrieved by ConfigProvider.getConfig(). Injected config property values should be the same as if retrieved from an injected Config instance via Config.getValue().

  • A factory method ConfigProvider#getConfig() to create a Config object based on automatically picked up ConfigSources of the Application identified by the current Thread Context ClassLoader classpath. The default and the auto discovered Converters will be gathered to form a configuration. Subsequent calls to this method for a certain Application will return the same Config instance.

  • A factory method ConfigProvider#getConfig(ClassLoader forClassLoader) to create a Config object based on automatically picked up ConfigSources of the Application identified by the given ClassLoader. The default and the auto discovered Converters will be gathered to form a configuration. This can be used if the Thread Context ClassLoader does not represent the correct layer. E.g. if you need the Config for a class in a shared EAR lib folder. Subsequent calls to this method for a certain Application will return the same Config instance.

  • A factory method ConfigProviderResolver#getBuilder() to create a ConfigBuilder object. The builder has no config sources. Only the default converters are added. The ConfigBuilder object can be filled manually via methods like ConfigBuilder#withSources(ConfigSources…​ sources). This configuration instance will by default not be shared by the ConfigProvider. This method is intended be used if a IoC container or any other external Factory can be used to give access to a manually created shared Config.

The Config object created via builder pattern can be managed as follows:

  • A factory method ConfigProviderResolver#registerConfig(Config config, ClassLoader classloader) can be used to register a Config within the application. This configuration instance will be shared by ConfigProvider#getConfig(). Any subsequent call to ConfigProvider#getConfig() will return the registered Config instance for this application.

  • A factory method ConfigProviderResolver#releaseConfig(Config config) to release the Config instance. This will unbind the current Config from the application. The ConfigSources that implement the java.io.Closeable interface will be properly destroyed. The Converters that implement the java.io.Closeable interface will be properly destroyed. Any subsequent call to ConfigProvider#getConfig() or ConfigProvider#getConfig(ClassLoader forClassLoader) will result in a new Config instance.

All methods in the ConfigProvider, ConfigProviderResolver and Config implementations are thread safe and reentrant.

The Config instances created via CDI are Serializable.

If a Config instance is created via @Inject Config or ConfigProvider#getConfig() or via the builder pattern but later called ConfigProviderResolver#registerConfig(Config config, Classloader classloader), the Config instance will be released when the application is closed.