使用lucene建立索引的问题

IndexFiles indexFiles=new IndexFiles();
File file = new File(request.getRealPath("1"));
IndexWriter writer= new IndexWriter(request.getRealPath("myindex"), new StandardAnalyzer(), true);
indexFiles.addIndex(writer,file);
writer.optimize();
writer.close();我每次尽力新索引的时候会覆盖掉旧的索引库但覆盖时就出错了?_r.cfs我自己手动删也删不掉除非把TOMCAT关闭才可以删 索引库应该是被Lock 请问怎么解锁?
java.io.IOException: Cannot delete _r.cfs
        at org.apache.lucene.store.FSDirectory.create(FSDirectory.java:144)
        at org.apache.lucene.store.FSDirectory.getDirectory(FSDirectory.java:105
)
        at org.apache.lucene.store.FSDirectory.getDirectory(FSDirectory.java:83)        at org.apache.lucene.index.IndexWriter.<init>(IndexWriter.java:173)
        at essp.SearcheServlet.doGet(SearcheServlet.java:75)
        at essp.SearcheServlet.doPost(SearcheServlet.java:110)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:763)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl
icationFilterChain.java:284)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF
ilterChain.java:204)