http://lucene.apache.org/lucene-parent/lucene-queryparser: Lucene QueryParsers module (The Apache Software Foundation) 
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package org.apache.lucene.queryparser.flexible.core.processors;

import org.apache.lucene.queryparser.flexible.core.QueryNodeException;
import org.apache.lucene.queryparser.flexible.core.config.QueryConfigHandler;
import org.apache.lucene.queryparser.flexible.core.nodes.QueryNode;


A QueryNodeProcessor is an interface for classes that process a QueryNode tree. 

The implementor of this class should perform some operation on a query node
tree and return the same or another query node tree.

 It also may carry a QueryConfigHandler object that contains configuration about the query represented by the query tree or the collection/index where it's intended to be executed. 
 In case there is any QueryConfigHandler associated to the query tree to be processed, it should be set using setQueryConfigHandler(QueryConfigHandler) before process(QueryNode) is invoked. 
See Also:
/**
 * A {@link QueryNodeProcessor} is an interface for classes that process a
 * {@link QueryNode} tree.
 * <p>
 * The implementor of this class should perform some operation on a query node
 * tree and return the same or another query node tree.
 * <p>
 * It also may carry a {@link QueryConfigHandler} object that contains
 * configuration about the query represented by the query tree or the
 * collection/index where it's intended to be executed.
 * <p>
 * In case there is any {@link QueryConfigHandler} associated to the query tree
 * to be processed, it should be set using
 * {@link QueryNodeProcessor#setQueryConfigHandler(QueryConfigHandler)} before
 * {@link QueryNodeProcessor#process(QueryNode)} is invoked.
 * 
 * @see QueryNode
 * @see QueryNodeProcessor
 * @see QueryConfigHandler
 */
public interface QueryNodeProcessor {

  
Processes a query node tree. It may return the same or another query tree.
I should never return null.

Params:
  • queryTree – 
         tree root node
Returns:the processed query tree
/**
   * Processes a query node tree. It may return the same or another query tree.
   * I should never return <code>null</code>.
   * 
   * @param queryTree
   *          tree root node
   * 
   * @return the processed query tree
   */
  public QueryNode process(QueryNode queryTree) throws QueryNodeException;

  
Sets the QueryConfigHandler associated to the query tree. 
/**
   * Sets the {@link QueryConfigHandler} associated to the query tree.
   */
  public void setQueryConfigHandler(QueryConfigHandler queryConfigHandler);

  
Returns the QueryConfigHandler associated to the query tree if any, otherwise it returns null

Returns:the QueryConfigHandler associated to the query tree if any, otherwise it returns null
/**
   * Returns the {@link QueryConfigHandler} associated to the query tree if any,
   * otherwise it returns <code>null</code>
   * 
   * @return the {@link QueryConfigHandler} associated to the query tree if any,
   *         otherwise it returns <code>null</code>
   */
  public QueryConfigHandler getQueryConfigHandler();

}