Solr之检索建议。

        检索建议目前是各大搜索的标配应用，主要作用是避免用户输入错误的搜索词，同时将用户引导到相应的关键词搜索上。Solr内置了检索建议功能，他在Solr里叫做Suggest模块。该模块可选择基于提示词文本做检索建议，还支持针对索引的某个字段建立索引词库来检索建议。在诸多文档中都推荐使用基于索引来做做检索建议，因此我们目前的实现也是采取该方案。

        现在我们开始配置Suggest模块，首先在solrconfig.xml文件中配置Suggest依赖的SpellCheck模块，然后再配置Suggest模块，所以这两个都需要配置。

<searchComponent name = "suggest" class = "solr.SpellCheckComponent">

<str name = "queryAnalyzerFieldType">string</str>

<lst name = "spellchecker">

<str name = "name">suggest</str>

<str name = "classname">org.apache.solr.spelling.suggest.Suggester</str>

<str name = "lookupImpl">org.apache.solr.spelling.suggest.TSTLookup</str>

<str name = "field">text</str>

<float name = "threshold">0.0001</float>

<str name = "spellcheckIndexDir">spellchecker</str>

<str name = "comparatorClass">freq</str>

<str name = "buildOnOptimize">true</str>

<!-- <str name = "buildOnCommit">true</str> -->

</lst>

</searchComponent>

<requestHandler name = "/suggest" class = "solr.SearchHandler" startup = "lazy">

<lst name = "defaults">

<str name = "spellcheck">true</str>

<str name = "spellcheck.dictionary">suggest</str>

<str name = "spellcheck.onlyMorePopular">true</str>

<str name = "spellcheck.extendedResults">false</str>

<str name = "spellcheck.count">10</str>

<str name = "spellcheck.collate">true</str>

</lst>

<arr name = "compontents">

<str>suggest</str>

</arr>

</requestHandler>

          配置完成之后，我们进行一下测试，重启Solr后，访问如下链接：

http://localhost:8080/solr/collection1/suggest?wt=xml&indent=true&spellcheck=true&spellcheck.q=%E4%B8%AD%E5%9B%BD

<?xml version = "1,0" encoding = "UTF-8"?>

<response>

<lst name = "responseHeader">

<int name= "status">0</int>

<int name= "QTime">4</int>

<lst>

<lst name = "spellcheck">

<lst name = "suggestions">

<lst name = "中国">

<int name= "numFound">4</int>

<int name= "startOffset">0</int>

<int name= "endOffset">2</int>

<arr name = "suggestion">

<str>中国队</str>

<str>中国证监会</str>

<str>中国足协</str>

<str>中国银行</str>

</arr>

</lst>

</lst>

</lst>

</response>

          使用Solr时也同样加入参数就可以。

SolrQuery query = new SolrQuery();

query.set("q" , token);

query.set("qt" , "/suggest");

query.set("spellcheck.count" , "10");

QueryResponse response = server.query(query);

SpellCheckResponse spellCheckResponse = response.getSpellCheckResponse();

if (spellCheckResponse != null ) {

List<SpellCheckResponse.Suggestion> suggestionList = spellCheckResponse.getSuggestions();

for (SpellCheckResponse.Suggestion suggestion : suggestionList) {

List<String> suggestedWordList = suggestion.getAlternatives();

for(int i = 0 ; i < suggestedWordList.size(); i ++) {

String word = suggestedWordList.get(i);

}

}

return results;

}

        通过threshold参数来限制一些不常用的词不出现在智能提示列表中，当这个值设置过大时，可能导致结果太少，需要引起注意。目前主要存在的问题是使用freq排序算法，返回的结果完全基于索引中字符的出现次数，没有兼顾用户搜索词语的频率，因此无法将一些热门词排在更靠前的位置。这块可定制SuggestWordScoreComparator来实现，目前还没有着手做这件事情。