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Lucene example source code file (MultiFieldQueryNodeProcessor.java)

This example Lucene source code file (MultiFieldQueryNodeProcessor.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

booleanquerynode, fieldablenode, fieldablenode, groupquerynode, linkedlist, linkedlist, multifieldattribute, multifieldquerynodeprocessor, override, override, queryconfighandler, querynode, querynodeexception, querynodeexception, util

The Lucene MultiFieldQueryNodeProcessor.java source code

package org.apache.lucene.queryParser.standard.processors;

/**
 * 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.
 */

import java.util.LinkedList;
import java.util.List;

import org.apache.lucene.queryParser.core.QueryNodeException;
import org.apache.lucene.queryParser.core.config.QueryConfigHandler;
import org.apache.lucene.queryParser.core.nodes.BooleanQueryNode;
import org.apache.lucene.queryParser.core.nodes.FieldableNode;
import org.apache.lucene.queryParser.core.nodes.GroupQueryNode;
import org.apache.lucene.queryParser.core.nodes.QueryNode;
import org.apache.lucene.queryParser.core.processors.QueryNodeProcessorImpl;
import org.apache.lucene.queryParser.standard.config.MultiFieldAttribute;

/**
 * This processor is used to expand terms so the query looks for the same term
 * in different fields. It also boosts a query based on its field. <br/>
 * <br/>
 * This processor looks for every {@link FieldableNode} contained in the query
 * node tree. If a {@link FieldableNode} is found, it checks if there is a
 * {@link MultiFieldAttribute} defined in the {@link QueryConfigHandler}. If
 * there is, the {@link FieldableNode} is cloned N times and the clones are
 * added to a {@link BooleanQueryNode} together with the original node. N is
 * defined by the number of fields that it will be expanded to. The
 * {@link BooleanQueryNode} is returned. <br/>
 * 
 * @see MultiFieldAttribute
 */
public class MultiFieldQueryNodeProcessor extends QueryNodeProcessorImpl {

  private boolean processChildren = true;

  public MultiFieldQueryNodeProcessor() {
    // empty constructor
  }

  @Override
  protected QueryNode postProcessNode(QueryNode node) throws QueryNodeException {

    return node;

  }

  @Override
  protected void processChildren(QueryNode queryTree) throws QueryNodeException {

    if (this.processChildren) {
      super.processChildren(queryTree);

    } else {
      this.processChildren = true;
    }

  }

  @Override
  protected QueryNode preProcessNode(QueryNode node) throws QueryNodeException {

    if (node instanceof FieldableNode) {
      this.processChildren = false;
      FieldableNode fieldNode = (FieldableNode) node;

      if (fieldNode.getField() == null) {

        if (!getQueryConfigHandler().hasAttribute(MultiFieldAttribute.class)) {
          throw new IllegalArgumentException(
              "MultiFieldAttribute should be set on the QueryConfigHandler");
        }

        CharSequence[] fields = getQueryConfigHandler().getAttribute(
            MultiFieldAttribute.class).getFields();

        if (fields != null && fields.length > 0) {
          fieldNode.setField(fields[0]);

          if (fields.length == 1) {
            return fieldNode;

          } else {
            LinkedList<QueryNode> children = new LinkedList();
            children.add(fieldNode);

            for (int i = 1; i < fields.length; i++) {
              try {
                fieldNode = (FieldableNode) fieldNode.cloneTree();
                fieldNode.setField(fields[i]);

                children.add(fieldNode);

              } catch (CloneNotSupportedException e) {
                // should never happen
              }

            }

            return new GroupQueryNode(new BooleanQueryNode(children));

          }

        }

      }

    }

    return node;

  }

  @Override
  protected List<QueryNode> setChildrenOrder(List children)
      throws QueryNodeException {

    return children;

  }

}

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