org.apache.lucene.queryParser.standard.processors
Class RemoveEmptyNonLeafQueryNodeProcessor

java.lang.Object
  org.apache.lucene.queryParser.core.processors.QueryNodeProcessorImpl
      org.apache.lucene.queryParser.standard.processors.RemoveEmptyNonLeafQueryNodeProcessor

All Implemented Interfaces:

QueryNodeProcessor

public class RemoveEmptyNonLeafQueryNodeProcessor
extends QueryNodeProcessorImpl

This processor removes every QueryNode that is not a leaf and has not children. If after processing the entire tree the root node is not a leaf and has no children, a MatchNoDocsQueryNode object is returned.

This processor is used at the end of a pipeline to avoid invalid query node tree structures like a GroupQueryNode or ModifierQueryNode with no children.

See Also:

QueryNode, MatchNoDocsQueryNode

Constructor Summary

RemoveEmptyNonLeafQueryNodeProcessor()

Method Summary

protected QueryNode	postProcessNode(QueryNode node) This method is invoked for every node when walking up the tree.
protected QueryNode	preProcessNode(QueryNode node) This method is invoked for every node when walking down the tree.
QueryNode	process(QueryNode queryTree) Processes a query node tree.
protected List<QueryNode>	setChildrenOrder(List<QueryNode> children) This method is invoked for every node that has at least on child.

Methods inherited from class org.apache.lucene.queryParser.core.processors.QueryNodeProcessorImpl

getQueryConfigHandler, processChildren, setQueryConfigHandler

Methods inherited from class java.lang.Object

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

Constructor Detail

RemoveEmptyNonLeafQueryNodeProcessor

public RemoveEmptyNonLeafQueryNodeProcessor()

Method Detail

process

public QueryNode process(QueryNode queryTree)
                  throws QueryNodeException

Description copied from interface: QueryNodeProcessor

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

Specified by:

process in interface QueryNodeProcessor

Overrides:

process in class QueryNodeProcessorImpl

Parameters:

queryTree - tree root node

Returns:

the processed query tree

Throws:

QueryNodeException

postProcessNode

protected QueryNode postProcessNode(QueryNode node)
                             throws QueryNodeException

Description copied from class: QueryNodeProcessorImpl

This method is invoked for every node when walking up the tree.

Specified by:

postProcessNode in class QueryNodeProcessorImpl

Parameters:

node - node the query node to be post-processed

Returns:

a query node

Throws:

QueryNodeException - if something goes wrong during the query node processing

preProcessNode

protected QueryNode preProcessNode(QueryNode node)
                            throws QueryNodeException

Description copied from class: QueryNodeProcessorImpl

This method is invoked for every node when walking down the tree.

Specified by:

preProcessNode in class QueryNodeProcessorImpl

Parameters:

node - the query node to be pre-processed

Returns:

a query node

Throws:

QueryNodeException - if something goes wrong during the query node processing

setChildrenOrder

protected List<QueryNode> setChildrenOrder(List<QueryNode> children)
                                    throws QueryNodeException

Description copied from class: QueryNodeProcessorImpl

This method is invoked for every node that has at least on child. It's invoked right before QueryNodeProcessorImpl.postProcessNode(QueryNode) is invoked.

Specified by:

setChildrenOrder in class QueryNodeProcessorImpl

Parameters:

children - the list containing all current node's children

Returns:

a new list containing all children that should be set to the current node

Throws:

QueryNodeException - if something goes wrong during the query node processing