在實際應用中，很多應用程式保持多個分離的Lucene索引，但有需要在搜尋過程中能夠將結果合併輸出，比如新聞網站每天都會建立不同索引，但是搜尋一個月的新聞時就需要合併輸出結果。這時可以使用如下方式：

mreader = new MultiReader(readera,readern);
        searcher = new IndexSearcher(mreader);//4.0以後的MultiSearcher替換成這樣

可以看到我們需要使用MultiReader這個類，將讀不同索引的reader封裝在一塊。
下面是實現程式碼

import java.io.IOException
 
;

import junit.framework.TestCase;

import org.apache.lucene.analysis.*;
import org.apache.lucene.analysis.core.*;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.StringField;
import org.apache.lucene.index.DirectoryReader;
import org.apache
 
.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.MultiReader;
import org.apache.lucene.search.*;
import org.apache.lucene.store.*;


public class MultiSearcherTest extends TestCase{
    private static IndexSearcher searcher;
 

    static IndexReader readera;
    static IndexReader readern;
    static MultiReader mreader;

    public static void testMulti() throws IOException{
        String[] animals = {
                "aardvark","beaver","coati","dog",
                "elephant","frog","gila monster",
                "horse","iguana","javelina","kangroo",
                "lemur","moose","rematode","orca",
                "python","quoka","rat","scorpion",
                "tarantula","uromastyx","vicuna",
                "walrus","xiphias","yak","zebra"
        };
        Analyzer analyzer = new WhitespaceAnalyzer();
        Directory aTOmDirectory = new RAMDirectory();//建立兩個目錄
        Directory nTOzDirectory = new RAMDirectory();
        IndexWriterConfig configa = new IndexWriterConfig(analyzer);
        IndexWriterConfig confign = new IndexWriterConfig(analyzer);
        IndexWriter aTOmWriter = new IndexWriter(aTOmDirectory,configa);
        IndexWriter nTOzWriter = new IndexWriter(nTOzDirectory,confign);

        for(int i = animals.length - 1;i >= 0;i--){
            Document doc = new Document();
            String animal  = animals[i];
            doc.add(new StringField("animal",animal,Field.Store.YES));
            if(animal.charAt(0) < 'n'){
                aTOmWriter.addDocument(doc);
            }else{ 
                nTOzWriter.addDocument(doc);
            }
        }


        readera = DirectoryReader.open(aTOmWriter,true);
        readern = DirectoryReader.open(nTOzWriter,true);
        aTOmWriter.close();
        nTOzWriter.close();
        mreader = new MultiReader(readera,readern);
        searcher = new IndexSearcher(mreader);//4.0以後的MultiSearcher替換成這樣
        TermRangeQuery query = TermRangeQuery.newStringRange("animal","h","t",true,true);
        TopDocs hits = searcher.search(query, 10);
        System.out.println("一共搜尋到結果："+hits.totalHits+"條");
        for(ScoreDoc s:hits.scoreDocs){
            Document doc = searcher.doc(s.doc);//通過序號得到檔案
            System.out.println("序號為"+s.doc+"   "+"animal:"+doc.get("animal"));
        }
        assertEquals("tarantula not included",12,hits.totalHits);
    }

    public static void main(String args[]) throws IOException{
        testMulti();
    }
}

TermRangeQuery類查詢包含從h到t開頭的動物名稱，匹配的文件來自於兩個不同的索引。結果如下：

當然上面程式是一個searcher單執行緒操作，也可以使用多執行緒的辦法，lucene5中提供了ParalleLeafReader類。