由于Lucene文件格式从2到3以及从3到4版本时都发生了重大的改变，造成了高版本无法读取低版本的数据，使用Lucene中的IndexUpgrader方法先将版本从2升到3，然后再从3升级到4。

import java.io.File;
import java.io.IOException;
import java.util.List;

import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexUpgrader;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.util.Version;


public class ConvertFromTwo {

    public static void main(String[] args) {
        ConvertFromTwo c = new ConvertFromTwo();
        c.upgrade();        
    }
    private final String INDEX_PATH = "C:/Users/rainystars/Desktop/index-synonym";  
    public void upgrade(){
        try {
            File dir = new File(INDEX_PATH);
            String path = "";
            String[] dirList = dir.list();
            for (String d:dirList){
                path = INDEX_PATH + "/" + d;
                IndexUpgrader t = new IndexUpgrader(FSDirectory.open(new File(path)),
        Version.LUCENE_36,null,true);
                t.upgrade();
                System.out.println(path+" Done.");
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println("All Done.");
    }
}

从版本2升级到版本3时，需要使用lucene3的jar包，我使用的lucene3.6的jar包，我需要处理的索引是在一个文件夹中所存在的一系列索引文件，所以需要循环来遍历每个目录。

import java.io.File;
import java.io.IOException;

import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexUpgrader;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.util.Version;

public class ConvertFromThree {

    public static void main(String[] args) {
        ConvertFromThree c = new ConvertFromThree();
        c.upgrade();        
    }
    private final String INDEX_PATH = "C:/Users/rainystars/Desktop/index-synonym";  
    public void upgrade(){
        try {
            File dir = new File(INDEX_PATH);
            String path = "";
            String[] dirList = dir.list();
            for (String d:dirList){
                path = INDEX_PATH + "/" + d;
                //System.out.println(path);
                IndexUpgrader t = new IndexUpgrader(FSDirectory.open(new File(path)),
                                                        Version.LUCENE_44,System.out,true);
                t.upgrade();
                System.out.println(path+" Done.");
            }       
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println("All Done.");
    }
}

在3到4版本的转化中使用的是lucene4.4的jar包