cannot make any changes to the index (it was opened with readOnly = true)

本文介绍在使用Lucene 3.0及以上版本时,因IndexReader默认只读属性导致删除索引时报UnsupportedOperationException异常的问题。提供了解决方案,即通过修改IndexReader.open方法并传递一个布尔型参数以禁用只读模式。

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在调用IndexReader.open(final Directory directory)时候,在lucene3.0以上的版本中新增加属性中的readOnly默认为true(readOnly true if no changes (deletions, norms) will be made with this IndexReader),导致在删除索引的时候抛出UnsupportedOperationException。
解决方法为:
1、IndexReader源码中添加方法:
public static IndexReader open(final String path, Boolean readOnly) throws
CorruptIndexException, IOException {
return open(FSDirectory.open(new File(path)), null, null,
readOnly, DEFAULT_TERMS_INDEX_DIVISOR);
}

2、应用代码中传递一参数:
IndexReader indexReader = IndexReader.open(indexDir,false);


源码解释如下:
/** Expert: returns an IndexReader reading the index in
* the given Directory, using a specific commit and with
* a custom {@link IndexDeletionPolicy}. You should pass
* readOnly=true, since it gives much better concurrent
* performance, unless you intend to do write operations
* (delete documents or change norms) with the reader.
* @param commit the specific {@link IndexCommit} to open;
* see {@link IndexReader#listCommits} to list all commits
* in a directory
* @param deletionPolicy a custom deletion policy (only used
* if you use this reader to perform deletes or to set
* norms); see {@link IndexWriter} for details.
* @param readOnly true if no changes (deletions, norms) will be made with this IndexReader
* @param termInfosIndexDivisor Subsamples which indexed
* terms are loaded into RAM. This has the same effect as {@link
* IndexWriter#setTermIndexInterval} except that setting
* must be done at indexing time while this setting can be
* set per reader. When set to N, then one in every
* N*termIndexInterval terms in the index is loaded into
* memory. By setting this to a value > 1 you can reduce
* memory usage, at the expense of higher latency when
* loading a TermInfo. The default value is 1. Set this
* to -1 to skip loading the terms index entirely. This is only useful in
* advanced situations when you will only .next() through all terms;
* attempts to seek will hit an exception.
*
* @throws CorruptIndexException if the index is corrupt
* @throws IOException if there is a low-level IO error
*/
public static IndexReader open(final IndexCommit commit, IndexDeletionPolicy deletionPolicy, boolean readOnly, int termInfosIndexDivisor) throws CorruptIndexException, IOException {
return open(commit.getDirectory(), deletionPolicy, commit, readOnly, termInfosIndexDivisor);
}
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