Package org.apache.commons.configuration2

## Class ConfigurationLookup

- java.lang.Object
- - org.apache.commons.configuration2.ConfigurationLookup

- All Implemented Interfaces:
    `Lookup`

      public class ConfigurationLookup
      extends Object
      implements Lookup

  A specialized implementation of the `Lookup` interface which uses a `Configuration` object to resolve variables.

  This class is passed an `ImmutableConfiguration` object at construction time. In its implementation of the `lookup()` method it simply queries this configuration for the passed in variable name. So the keys passed to `lookup()` are mapped directly to configuration properties.

  Since:
    2.0

- - ### Constructor Summary

    Constructors
    Constructor | Description
    --- | ---
    `ConfigurationLookup​(ImmutableConfiguration config)` | Creates a new instance of `ConfigurationLookup` and sets the associated `ImmutableConfiguration`.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `ImmutableConfiguration` | `getConfiguration()` | Gets the `ImmutableConfiguration` used by this object.
    `Object` | `lookup​(String variable)` | Looks up the value of the specified variable.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### ConfigurationLookup

          public ConfigurationLookup​(ImmutableConfiguration config)

      Creates a new instance of `ConfigurationLookup` and sets the associated `ImmutableConfiguration`.
      Parameters:
        `config` - the configuration to use for lookups (must not be null)
      Throws:
        `IllegalArgumentException` - if the configuration is null

  - ### Method Detail

    - #### getConfiguration

          public ImmutableConfiguration getConfiguration()

      Gets the `ImmutableConfiguration` used by this object.
      Returns:
        the associated `ImmutableConfiguration`

    - #### lookup

          public Object lookup​(String variable)

      Looks up the value of the specified variable. This method is called by `ConfigurationInterpolator` with the variable name extracted from the expression to interpolate (i.e. the prefix name has already been removed). A concrete implementation has to return the value of this variable or null if the variable name is unknown. This implementation calls `getProperty()` on the associated configuration. The return value is directly returned. Note that this may be a complex object, e.g. a collection or an array.
      Specified by:
        `lookup` in interface `Lookup`
      Parameters:
        `variable` - the name of the variable to be resolved
      Returns:
        the value of this variable or null