IndexSearcher
搜索引擎的构建分为索引内容和查询索引两个大方面，这里要介绍的是lucene索引查询器即IndexSearcher的构建过程；
首先了解下IndexSearcher：
IndexSearcher提供了对单个IndexReader的查询实现；
我们对索引的查询，可以通过调用search(Query,n)或者search(Query,Filter,n)方法；
在索引内容变动不大的情况下，我们可以对索引的搜索采用单个IndexSearcher共享的方式来提升性能；
如果索引有变动，我们就需要使用DirectoryReader.openIfChanged(DirectoryReader)来获取新的reader，然后创建新的IndexSearcher对象；
为了使查询延迟率低，我们最好使用近实时搜索的方法（此时我们的DirectoryReader的构建就要采用DirectoryReader.open(IndexWriter, boolean)）
IndexSearcher实例是完全线程安全的,这意味着多个线程可以并发调用任何方法。如果需要外部同步,无需添加IndexSearcher的同步；
IndexSearcher的创建过程
Directory dir = FSDirectory.open(Paths.get(indexDir));
根据索引文件路径创建FSDirectory的实例，返回的FSDirectory实例跟系统或运行环境有关，对于Linux, MacOSX, Solaris, and Windows 64-bit JREs返回的是一个MMapDirectory实例，对于其他非windows JREs环境返回的是NIOFSDirectory，而对于其他Windows的JRE环境返回的是SimpleFSDirectory，其执行效率依次降低
// 通过dir得到的路径下的所有的文件
IndexReader reader = DirectoryReader.open(dir);
接着DirectoryReader根据获取到的FSDirectory实例读取索引文件并得到DirectoryReader对象；DirectoryReader的open方法返回实例的原理：
读取索引目录中的Segments文件内容，倒序遍历SegmentInfos并填充到SegmentReader（IndexReader的一种实现）数组，并构建StandardDirectoryReader的实例
/** called from DirectoryReader.open(...) methods */
static DirectoryReader open(final Directory directory, final IndexCommit commit) throws IOException {
return new SegmentInfos.FindSegmentsFile<DirectoryReader>(directory) {
@Override
protected DirectoryReader doBody(String segmentFileName) throws IOException {
SegmentInfos sis = SegmentInfos.readCommit(directory, segmentFileName);
final SegmentReader[] readers = new SegmentReader[sis.size()];
boolean success = false;
try {
for (int i = sis.size()-1; i >= 0; i--) {
readers[i] = new SegmentReader(sis.info(i), sis.getIndexCreatedVersionMajor(), IOContext.READ);
}
// This may throw CorruptIndexException if there are too many docs, so
// it must be inside try clause so we close readers in that case:
DirectoryReader reader = new StandardDirectoryReader(directory, readers, null, sis, false, false);
success = true;
return reader;
} finally {
if (success == false) {
IOUtils.closeWhileHandlingException(readers);
}
}
}
}.run(commit);
}
有了IndexReader，IndexSearcher对象实例化就手到拈来了，new IndexSearcher(DirectoryReader)就可以得到其实例；如果我们想提高IndexSearcher的执行效率可以new IndexSearcher(DirecotoryReader,ExcuterService)来创建IndexSearcher对象，这样做的好处为对每块segment采用了分工查询，但是要注意IndexSearcher并不维护ExcuterService的生命周期，我们还需要自行调用ExcuterService的close/awaitTermination
源码
以下是根据IndexSearcher相关的构建过程及其特性编写的一个搜索的工具类
ps: 因为版本的差异，实现也会有差异。下面的仅供参考，后续会进行统一的优化。
package com.github.houbb.lucene.learn.chap05;
import com.github.houbb.lucene.learn.chap04.IndexUtil;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.*;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.MultiReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.*;
import org.apache.lucene.search.SortField.Type;
import org.apache.lucene.store.FSDirectory;
import java.io.File;
import java.io.IOException;
import java.nio.file.Paths;
import java.util.concurrent.ExecutorService;
/**
* @author binbin.hou
* @since 1.0.0
*/
public class SearcherUtil {
public static final Analyzer analyzer = new StandardAnalyzer();
/**获取IndexSearcher对象（适合单索引目录查询使用）
* @param indexPath 索引目录
* @return
* @throws IOException
* @throws InterruptedException
*/
public static IndexSearcher getIndexSearcher(String indexPath, ExecutorService service, boolean realtime) throws IOException, InterruptedException{
DirectoryReader reader = DirectoryReader.open(IndexUtil.getIndexWriter(indexPath, true), realtime, realtime);
IndexSearcher searcher = new IndexSearcher(reader,service);
if(service != null){
service.shutdown();
}
return searcher;
}
/**多目录多线程查询
* @param parentPath 父级索引目录
* @param service 多线程查询
* @return
* @throws IOException
* @throws InterruptedException
*/
public static IndexSearcher getMultiSearcher(String parentPath,ExecutorService service,boolean realtime) throws IOException, InterruptedException{
MultiReader multiReader;
File file = new File(parentPath);
File[] files = file.listFiles();
IndexReader[] readers = new IndexReader[files.length];
if(!realtime){
for (int i = 0 ; i < files.length ; i ++) {
readers[i] = DirectoryReader.open(FSDirectory.open(Paths.get(files[i].getPath(), new String[0])));
}
}else{
for (int i = 0 ; i < files.length ; i ++) {
readers[i] = DirectoryReader.open(IndexUtil.getIndexWriter(files[i].getPath(), true), true, true);
}
}
multiReader = new MultiReader(readers);
IndexSearcher searcher = new IndexSearcher(multiReader,service);
if(service != null){
service.shutdown();
}
return searcher;
}
/**从指定配置项中查询
* @return
* @param field 字段
* @param fieldType 字段类型
* @param queryStr 查询条件
* @param range 是否区间查询
* @return
*/
public static Query getQuery(String field,String fieldType,String queryStr,boolean range){
Query q = null;
if(queryStr != null && !"".equals(queryStr)){
if(range){
String[] strs = queryStr.split("\\|");
if("int".equals(fieldType)){
int min = new Integer(strs[0]);
int max = new Integer(strs[1]);
q = IntPoint.newRangeQuery(field, min, max);
}else if("double".equals(fieldType)){
Double min = new Double(strs[0]);
Double max = new Double(strs[1]);
q = DoublePoint.newRangeQuery(field, min, max);
}else if("float".equals(fieldType)){
Float min = new Float(strs[0]);
Float max = new Float(strs[1]);
q = FloatPoint.newRangeQuery(field, min, max);
}else if("long".equals(fieldType)){
Long min = new Long(strs[0]);
Long max = new Long(strs[1]);
q = LongPoint.newRangeQuery(field, min, max);
}
}else{
if("int".equals(fieldType)){
q = IntPoint.newRangeQuery(field, new Integer(queryStr), new Integer(queryStr));
}else if("double".equals(fieldType)){
q = DoublePoint.newRangeQuery(field, new Double(queryStr), new Double(queryStr));
}else if("float".equals(fieldType)){
q = FloatPoint.newRangeQuery(field, new Float(queryStr), new Float(queryStr));
}else{
Term term = new Term(field, queryStr);
q = new TermQuery(term);
}
}
}else{
q= new MatchAllDocsQuery();
}
System.out.println(q);
return q;
}
/**对多个条件进行排序构建排序条件
* @param fields
* @param types
* @param reverses
* @return
*/
public static Sort getSortInfo(String[] fields,Type[] types,boolean[] reverses){
SortField[] sortFields = null;
int fieldLength = fields.length;
int typeLength = types.length;
int reverLength = reverses.length;
if(!(fieldLength == typeLength) || !(fieldLength == reverLength)){
return null;
}else{
sortFields = new SortField[fields.length];
for (int i = 0; i < fields.length; i++) {
sortFields[i] = new SortField(fields[i], types[i], reverses[i]);
}
}
return new Sort(sortFields);
}
/**根据查询器、查询条件、每页数、排序条件进行查询
* @param query 查询条件
* @param first 起始值
* @param max 最大值
* @param sort 排序条件
* @return
*/
public static TopDocs getScoreDocsByPerPageAndSortField(IndexSearcher searcher,Query query, int first,int max, Sort sort){
try {
if(query == null){
System.out.println(" Query is null return null ");
return null;
}
TopFieldCollector collector = null;
if(sort != null){
collector = TopFieldCollector.create(sort, first+max, false, false, false);
}else{
sort = new Sort(new SortField[]{new SortField("modified", SortField.Type.LONG)});
collector = TopFieldCollector.create(sort, first+max, false, false, false);
}
searcher.search(query, collector);
return collector.topDocs(first, max);
} catch (IOException e) {
// TODO Auto-generated catch block
}
return null;
}
/**获取上次索引的id,增量更新使用
* @return
*/
public static Integer getLastIndexBeanID(IndexReader multiReader){
Query query = new MatchAllDocsQuery();
IndexSearcher searcher = null;
searcher = new IndexSearcher(multiReader);
SortField sortField = new SortField("id", SortField.Type.INT,true);
Sort sort = new Sort(new SortField[]{sortField});
TopDocs docs = getScoreDocsByPerPageAndSortField(searcher,query, 0, 1, sort);
ScoreDoc[] scoreDocs = docs.scoreDocs;
int total = scoreDocs.length;
if(total > 0){
ScoreDoc scoreDoc = scoreDocs[0];
Document doc = null;
try {
doc = searcher.doc(scoreDoc.doc);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return new Integer(doc.get("id"));
}
return 0;
}
}
