昨天我们了解了lucene搜索之IndexSearcher构建过程（），对lucene的IndexSearcher有一个大体的了解，知道了怎么创建IndexSearcher，就要开始学会使用IndexSearcher进行索引的搜索，本节我们学习索引的查询原理和根据其相关原理写索引查询的工具类的编写；IndexSearcher常用方法
IndexSearcher提供了几个常用的方法：
IndexSearcher.doc(int docID) 获取索引文件中的第n个索引存储的相关字段，返回为Document类型，可以据此读取document中的Field.STORE.YES的字段；IndexSearcher.doc(int docID, StoredFieldVisitor fieldVisitor) 获取StoredFieldVisitor指定的字段的document，StoredFieldVisitor定义如下StoredFieldVisitor visitor = new DocumentStoredFieldVisitor(String… fields);IndexSearcher.doc(int docID, Set<String> fieldsToLoad) 此方法同上边的IndexSearcher.doc(int docID, StoredFieldVisitor fieldVisitor)，其实现如下图
IndexSearcher.count(Query query) 统计符合query条件的document个数
IndexSearcher.searchAfter(final ScoreDoc after, Query query, int numHits) 此方法会返回符合query查询条件的且在after之后的numHits条记录；
其实现原理为：
先读取当前索引文件的最大数据条数limit，然后判断after是否为空和after对应的document的下标是否超出limit的限制，如果超出的话抛出非法的参数异常；
设置读取的条数为numHits和limit中最小的（因为有超出最大条数的可能，避免超出限制而造成的异常）
接下来创建一个CollectorManager类型的对象，该对象定义了要返回的TopDocs的个数，上一页的document的结尾（after）,并且对查询结果进行分析合并
最后调用search(query,manager)来查询结果
先判断是否有ExecutorService执行查询的任务，如果没有executor，IndexSearcher会在单个任务下进行查询操作；
如果IndexSearcher有executor，则会由每个线程控制一部分索引的读取，而且查询的过程中采用的是future机制，此种方式是边读边往结果集里边追加数据，这种异
步的处理机制也提升了效率，其执行过程如下：
编码实践
我中午的时候写了一个SearchUtil的工具类，里边添加了多目录查询和分页查询的功能，经测试可用，工具类和测试的代码如下：
package com.lucene.search.util;import java.io.File;import java.io.IOException;import java.nio.file.Paths;import java.util.Set;import java.util.concurrent.ExecutorService;import org.apache.lucene.document.Document;import org.apache.lucene.index.DirectoryReader;import org.apache.lucene.index.IndexReader;import org.apache.lucene.index.MultiReader;import org.apache.lucene.search.BooleanQuery;import org.apache.lucene.search.IndexSearcher;import org.apache.lucene.search.Query;import org.apache.lucene.search.ScoreDoc;import org.apache.lucene.search.TopDocs;import org.apache.lucene.search.BooleanClause.Occur;import org.apache.lucene.store.FSDirectory;/**lucene索引查询工具类 * @author lenovo * */public class SearchUtil {/**获取IndexSearcher对象 * @param indexPath * @param service * @return * @throws IOException */public static IndexSearcher getIndexSearcherByParentPath(String parentPath,ExecutorService service) throws IOException{MultiReader reader = null;//设置try {File[] files = new File(parentPath).listFiles();IndexReader[] readers = new IndexReader[files.length];for (int i = 0 ; i < files.length ; i ++) {readers[i] = DirectoryReader.open(FSDirectory.open(Paths.get(files[i].getPath(), new String[0])));}reader = new MultiReader(readers);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}return new IndexSearcher(reader,service);}/**根据索引路径获取IndexReader * @param indexPath * @return * @throws IOException */public static DirectoryReader getIndexReader(String indexPath) throws IOException{return DirectoryReader.open(FSDirectory.open(Paths.get(indexPath, new String[0])));}/**根据索引路径获取IndexSearcher * @param indexPath * @param service * @return * @throws IOException */public static IndexSearcher getIndexSearcherByIndexPath(String indexPath,ExecutorService service) throws IOException{IndexReader reader = getIndexReader(indexPath);return new IndexSearcher(reader,service);}/**如果索引目录会有变更用此方法获取新的IndexSearcher这种方式会占用较少的资源 * @param oldSearcher * @param service * @return * @throws IOException */public static IndexSearcher getIndexSearcherOpenIfChanged(IndexSearcher oldSearcher,ExecutorService service) throws IOException{DirectoryReader reader = (DirectoryReader) oldSearcher.getIndexReader();DirectoryReader newReader = DirectoryReader.openIfChanged(reader);return new IndexSearcher(newReader, service);}/**多条件查询类似于sql in * @param querys * @return */public static Query getMultiQueryLikeSqlIn(Query … querys){BooleanQuery query = new BooleanQuery();for (Query subQuery : querys) {query.add(subQuery,Occur.SHOULD);}return query;}/**多条件查询类似于sql and * @param querys * @return */public static Query getMultiQueryLikeSqlAnd(Query … querys){BooleanQuery query = new BooleanQuery();for (Query subQuery : querys) {query.add(subQuery,Occur.MUST);}return query;}/**根据IndexSearcher和docID获取默认的document * @param searcher * @param docID * @return * @throws IOException */public static Document getDefaultFullDocument(IndexSearcher searcher,int docID) throws IOException{return searcher.doc(docID);}/**根据IndexSearcher和docID * @param searcher * @param docID * @param listField * @return * @throws IOException */public static Document getDocumentByListField(IndexSearcher searcher,int docID,Set<String> listField) throws IOException{return searcher.doc(docID, listField);}/**分页查询 * @param page 当前页数 * @param perPage 每页显示条数 * @param searcher searcher查询器 * @param query 查询条件 * @return * @throws IOException */public static TopDocs getScoreDocsByPerPage(int page,int perPage,IndexSearcher searcher,Query query) throws IOException{TopDocs result = null;if(query == null){System.out.println(" Query is null return null ");return null;}ScoreDoc before = null;if(page != 1){TopDocs docsBefore = searcher.search(query, (page-1)*perPage);ScoreDoc[] scoreDocs = docsBefore.scoreDocs;if(scoreDocs.length > 0){before = scoreDocs[scoreDocs.length – 1];}}result = searcher.searchAfter(before, query, perPage);return result;}public static TopDocs getScoreDocs(IndexSearcher searcher,Query query) throws IOException{TopDocs docs = searcher.search(query, getMaxDocId(searcher));return docs;}/**统计document的数量,此方法等同于matchAllDocsQuery查询 * @param searcher * @return */public static int getMaxDocId(IndexSearcher searcher){return searcher.getIndexReader().maxDoc();}}
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