Lucene7 的加权检索（Boost）

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总体来说，lucene可以设置两个阶段的权重：

• 建立索引时对文档设置权重：

然而，在lucene 7.0发布时移除了索引时boost:

LUCENE-6819: Index-time boosts are not supported anymore. As a replacement, index-time scoring factors should be indexed into a doc value field and combined at query time using eg. FunctionScoreQuery.

http://archive.apache.org/dist/lucene/java/7.0.0/changes/Changes.html#v7.0.0.api_changes

• 检索时，对检索词设置权重：

而网上一大堆的答案都是 Query.setBoost() 或者 Query.createWeight() 然而：

LUCENE-6590: Query.setBoost(), Query.getBoost() and Query.clone() are gone. In order to apply boosts, you now need to wrap queries in a BoostQuery.
(Adrien Grand)

http://archive.apache.org/dist/lucene/java/6.6.0/changes/Changes.html

所以使用 BoostQuery 进行一下包装就好了：

TermQuery termQuery = new TermQuery(term);
BoostQuery query =new BoostQuery(termQuery, 0.5f);
// 若使用 BooleanQuery 进行查询时：
booleanQueryBuilder.add(query, BooleanClause.Occur.SHOULD);
BooleanQuery booleanQuery = booleanQueryBuilder.build();
log.info("lucene search terms：{}", booleanQuery.toString("question"));

这时候日志应该记录如下：