org.apache.lucene.document.LazyDocument.java Source code

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Here is the source code for org.apache.lucene.document.LazyDocument.java

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/*
 * 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.lucene.document;

import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexableField;
import org.apache.lucene.index.IndexableFieldType;
import org.apache.lucene.util.BytesRef;

/** Defers actually loading a field's value until you ask
 *  for it.  You must not use the returned Field instances
 *  after the provided reader has been closed. 
 * @see #getField
 */
public class LazyDocument {
    private final IndexReader reader;
    private final int docID;

    // null until first field is loaded
    private Document doc;

    private Map<Integer, List<LazyField>> fields = new HashMap<>();
    private Set<String> fieldNames = new HashSet<>();

    public LazyDocument(IndexReader reader, int docID) {
        this.reader = reader;
        this.docID = docID;
    }

    /**
     * Creates a StorableField whose value will be lazy loaded if and 
     * when it is used. 
     * <p>
     * <b>NOTE:</b> This method must be called once for each value of the field 
     * name specified in sequence that the values exist.  This method may not be 
     * used to generate multiple, lazy, StorableField instances referring to 
     * the same underlying StorableField instance.
     * </p>
     * <p>
     * The lazy loading of field values from all instances of StorableField 
     * objects returned by this method are all backed by a single StoredDocument 
     * per LazyDocument instance.
     * </p>
     */
    public IndexableField getField(FieldInfo fieldInfo) {

        fieldNames.add(fieldInfo.name);
        List<LazyField> values = fields.get(fieldInfo.number);
        if (null == values) {
            values = new ArrayList<>();
            fields.put(fieldInfo.number, values);
        }

        LazyField value = new LazyField(fieldInfo.name, fieldInfo.number);
        values.add(value);

        synchronized (this) {
            // edge case: if someone asks this LazyDoc for more LazyFields
            // after other LazyFields from the same LazyDoc have been
            // actuallized, we need to force the doc to be re-fetched
            // so the new LazyFields are also populated.
            doc = null;
        }
        return value;
    }

    /** 
     * non-private for test only access
     * @lucene.internal 
     */
    synchronized Document getDocument() {
        if (doc == null) {
            try {
                doc = reader.document(docID, fieldNames);
            } catch (IOException ioe) {
                throw new IllegalStateException("unable to load document", ioe);
            }
        }
        return doc;
    }

    // :TODO: synchronize to prevent redundent copying? (sync per field name?)
    private void fetchRealValues(String name, int fieldNum) {
        Document d = getDocument();

        List<LazyField> lazyValues = fields.get(fieldNum);
        IndexableField[] realValues = d.getFields(name);

        assert realValues.length <= lazyValues.size() : "More lazy values then real values for field: " + name;

        for (int i = 0; i < lazyValues.size(); i++) {
            LazyField f = lazyValues.get(i);
            if (null != f) {
                f.realValue = realValues[i];
            }
        }
    }

    /** 
     * @lucene.internal 
     */
    public class LazyField implements IndexableField {
        private String name;
        private int fieldNum;
        volatile IndexableField realValue = null;

        private LazyField(String name, int fieldNum) {
            this.name = name;
            this.fieldNum = fieldNum;
        }

        /** 
         * non-private for test only access
         * @lucene.internal 
         */
        public boolean hasBeenLoaded() {
            return null != realValue;
        }

        private IndexableField getRealValue() {
            if (null == realValue) {
                fetchRealValues(name, fieldNum);
            }
            assert hasBeenLoaded() : "field value was not lazy loaded";
            assert realValue.name().equals(name()) : "realvalue name != name: " + realValue.name() + " != "
                    + name();

            return realValue;
        }

        @Override
        public String name() {
            return name;
        }

        @Override
        public BytesRef binaryValue() {
            return getRealValue().binaryValue();
        }

        @Override
        public String stringValue() {
            return getRealValue().stringValue();
        }

        @Override
        public Reader readerValue() {
            return getRealValue().readerValue();
        }

        @Override
        public Number numericValue() {
            return getRealValue().numericValue();
        }

        @Override
        public IndexableFieldType fieldType() {
            return getRealValue().fieldType();
        }

        @Override
        public TokenStream tokenStream(Analyzer analyzer, TokenStream reuse) {
            return getRealValue().tokenStream(analyzer, reuse);
        }
    }
}