Package org.apache.commons.configuration2.interpol

Interface Lookup

  • All Known Implementing Classes:
    ConfigurationLookup, ConstantLookup, DummyLookup, EnvironmentLookup, ExprLookup, SystemPropertiesLookup
    public interface Lookup

    Definition of an interface for looking up variables during interpolation.

    Objects implementing this interface can be assigned a variable prefix and added to a ConfigurationInterpolator object. Whenever the ConfigurationInterpolator encounters a property value referencing a variable, e.g. ${prefix:variableName}, it extracts the prefix and finds the matching Lookup object. Then this object is asked to resolve the variable name and provide the corresponding value.

    This interface defines a single method for performing variable lookup. It is passed the name of a variable and has to return the corresponding value. It is of course up to a specific implementation how this is done. If the variable name cannot be resolved, an implementation has to return null.

    Note: Implementations must be aware that they can be accessed concurrently. This is for instance the case if a configuration object is read by multiple threads or if a Lookup object is shared by multiple configurations.

    Since:
    2.0

    • Method Detail

      • lookup

        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.
        Parameters:
        variable - the name of the variable to be resolved
        Returns:
        the value of this variable or null