Similarity改变solr的打分机制；
solr本身已经提供了几种算法
代码语言：javascript复制org.apache.solr.search.similarities.BM25SimilarityFactory
org.apache.solr.search.similarities.DefaultSimilarityFactory
org.apache.solr.search.similarities.DFRSimilarityFactory
org.apache.solr.search.similarities.IBSimilarityFactory
org.apache.solr.search.similarities.LMDirichletSimilarityFactory
org.apache.solr.search.similarities.LMJelinekMercerSimilarityFactory
org.apache.solr.search.similarities.SchemaSimilarityFactory可以在managed-schema下面添加：
<similarity class="org.apache.solr.search.similarities.SchemaSimilarityFactory"/>
<similarity class="org.apache.solr.search.similarities.BM25SimilarityFactory"/>
<similarity class="org.apache.solr.search.similarities.DefaultSimilarityFactory"/>
.....
测试会发现不同相似度计算方法检索上的差异：
