io.vertx.config

## Interface ConfigRetriever

-     public interface ConfigRetriever

  Defines a configuration retriever that read configuration from `ConfigStore` and tracks changes periodically.
  Author:
    Clement Escoffier

- - ### Method Summary

    All Methods Static Methods Instance Methods Abstract Methods Default Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `close()` Closes the retriever.
    `ReadStream<JsonObject>` | `configStream()`
    `static ConfigRetriever` | `create(Vertx vertx)` Creates an instance of the default implementation of the `ConfigRetriever`, using the default settings (json file, system properties and environment variables).
    `static ConfigRetriever` | `create(Vertx vertx, ConfigRetrieverOptions options)` Creates an instance of the default implementation of the `ConfigRetriever`.
    `JsonObject` | `getCachedConfig()` Gets the last computed configuration.
    `Future<JsonObject>` | `getConfig()` Like `getConfig(Handler)` but returns a `Future` of the asynchronous result
    `void` | `getConfig(Handler<AsyncResult<JsonObject>> completionHandler)` Reads the configuration from the different `ConfigStore` and computes the final configuration.
    `void` | `listen(Handler<ConfigChange> listener)` Registers a listener receiving configuration changes.
    `ConfigRetriever` | `setBeforeScanHandler(Handler<Void> handler)` Registers a handler called before every scan.
    `ConfigRetriever` | `setConfigurationProcessor(java.util.function.Function<JsonObject,JsonObject> processor)` Registers a handler that process the configuration before being injected into `getConfig(Handler)` or `listen(Handler)`.

- - ### Method Detail

    - #### create

          static ConfigRetriever create(Vertx vertx,
                                        ConfigRetrieverOptions options)

      Creates an instance of the default implementation of the `ConfigRetriever`.
      Parameters:
        `vertx` - the vert.x instance
        `options` - the options, must not be `null`, must contain the list of configured store.
      Returns:
        the created instance.

    - #### create

          static ConfigRetriever create(Vertx vertx)

      Creates an instance of the default implementation of the `ConfigRetriever`, using the default settings (json file, system properties and environment variables).
      Parameters:
        `vertx` - the vert.x instance
      Returns:
        the created instance.

    - #### getConfig

          void getConfig(Handler<AsyncResult<JsonObject>> completionHandler)

      Reads the configuration from the different `ConfigStore` and computes the final configuration.
      Parameters:
        `completionHandler` - handler receiving the computed configuration, or a failure if the configuration cannot be retrieved

    - #### getConfig

          Future<JsonObject> getConfig()

      Like `getConfig(Handler)` but returns a `Future` of the asynchronous result

    - #### close

          void close()

      Closes the retriever.

    - #### getCachedConfig

          JsonObject getCachedConfig()

      Gets the last computed configuration.
      Returns:
        the last configuration

    - #### listen

          void listen(Handler<ConfigChange> listener)

      Registers a listener receiving configuration changes. This method cannot only be called if the configuration is broadcasted.
      Parameters:
        `listener` - the listener

    - #### setBeforeScanHandler

          ConfigRetriever setBeforeScanHandler(Handler<Void> handler)

      Registers a handler called before every scan. This method is mostly used for logging purpose.
      Parameters:
        `handler` - the handler, must not be `null`
      Returns:
        the current config retriever

    - #### setConfigurationProcessor

          ConfigRetriever setConfigurationProcessor(java.util.function.Function<JsonObject,JsonObject> processor)

      Registers a handler that process the configuration before being injected into `getConfig(Handler)` or `listen(Handler)`. This allows the code to customize the configuration.
      Parameters:
        `processor` - the processor, must not be `null`. The method must not return `null`. The returned configuration is used. If the processor does not update the configuration, it must return the input configuration. If the processor throws an exception, the failure is passed to the `getConfig(Handler)` handler.
      Returns:
        the current config retriever

    - #### configStream

          ReadStream<JsonObject> configStream()

      Returns:
        the stream of configurations. It's single stream (unicast) and that delivers the last known config and the successors periodically.

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