https://commons.apache.org/proper/commons-configuration/: Tools to assist in the reading of configuration/preferences files in various formats (The Apache Software Foundation)
  • Konstantin Shaposhnikov (scand.com)
  • Jamie M. Guillemette (TD Bank)
  • Jorge Ferrer ()
  • Gabriele Garuglieri (Infoblu S.p.A)
  • Nicolas De Loof (Cap Gemini)
  • Oliver Kopp
  • Dennis Kieselhorst (IRIAN Deutschland)
  • Raviteja Lokineni
  • Vincent Maurin (glispa GmbH)
  • The Alchemist
  • Pascal Essiembre (Norconex Inc.)
  • Patrick Schmidt
  • Daniel Rall (CollabNet, Inc.)
  • Jason van Zyl (Zenplex)
  • Martin Poeschl (tucana.at)
  • dIon Gillard (Multitask Consulting)
  • Henning P. Schmiedehausen (INTERMETA - Gesellschaft fuer Mehrwertdienste mbH)
  • Eric Pugh (upstate.com)
  • Brian E. Dunbar (dunbarconsulting.org)
  • Emmanuel Bourg (Ariane Software)
  • Oliver Heger (Bosch Software Innovations)
  • Jörg Schaible
  • Ralph Goers (Intuit)
  • Gary Gregory (Rocket Software)
  • Claude Warren
  • Rob Tompkins 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration2.interpol;



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
/**
 * <p>
 * Definition of an interface for looking up variables during interpolation.
 * </p>
 * <p>
 * Objects implementing this interface can be assigned a variable prefix and
 * added to a {@link ConfigurationInterpolator} object. Whenever the
 * {@code ConfigurationInterpolator} encounters a property value referencing a
 * variable, e.g. <code>${prefix:variableName}</code>, it extracts the prefix
 * and finds the matching {@code Lookup} object. Then this object is asked to
 * resolve the variable name and provide the corresponding value.
 * </p>
 * <p>
 * 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
 * <b>null</b>.
 * </p>
 * <p>
 * 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 {@code Lookup} object is shared by multiple configurations.
 * </p>
 *
 * @since 2.0
 */
public interface Lookup
{
    
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.

Params:
  • variable – the name of the variable to be resolved
Returns:the value of this variable or null
/**
     * Looks up the value of the specified variable. This method is called by
     * {@link 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 <b>null</b> if the variable name is unknown.
     *
     * @param variable the name of the variable to be resolved
     * @return the value of this variable or <b>null</b>
     */
    Object lookup(String variable);
}