Elastic Search 实现返回结果高亮

众所周知，Google、百度等搜索引擎在返回查询结果时都会有高亮处理，让用户能够方便地快速识别出内容相关性。

在 elastic search 中也提供了 highlight 高亮功能，可以返回与检索词相关的句子，以确认查询结果相关性。

JSON 接口实现高亮

查询条件增加一个新的 highlight 参数：

GET /megacorp/employee/_search
{
    "query" : {
        "match_phrase" : {
            "about" : "rock climbing"
        }
    },
    "highlight": {
        "fields" : {
            "about" : {}
        }
    }
}

当执行该查询时，返回结果与之前一样，与此同时结果中还多了一个叫做 highlight 的部分。这个部分包含了 about 属性匹配的文本片段，并以 HTML 标签 <em></em> 封装：

{
   ...
   "hits": {
      "total":      1,
      "max_score":  0.23013961,
      "hits": [
         {
            ...
            "_score":         0.23013961,
            "_source": {
               "first_name":  "John",
               "last_name":   "Smith",
               "age":         25,
               "about":       "I love to go rock climbing",
               "interests": [ "sports", "music" ]
            },
            "highlight": {
               "about": [
                  "I love to go <em>rock</em> <em>climbing</em>" 
               ]
            }
         }
      ]
   }
}

Java 客户端实现高亮

在 SearchSourceBuilder 中设置一个 HighlightBuilder，可以用于设置高亮的字段。

SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
HighlightBuilder highlightBuilder = new HighlightBuilder(); 
HighlightBuilder.Field highlightTitle = new HighlightBuilder.Field("title"); 
highlightTitle.highlighterType("unified");  
highlightBuilder.field(highlightTitle);  
HighlightBuilder.Field highlightUser = new HighlightBuilder.Field("user");
highlightBuilder.field(highlightUser);
searchSourceBuilder.highlighter(highlightBuilder);

在搜索返回结果中获取高亮字段的内容。

SearchHits hits = searchResponse.getHits();
for (SearchHit hit : hits.getHits()) {
    Map<String, HighlightField> highlightFields = hit.getHighlightFields();
    HighlightField highlight = highlightFields.get("title"); 
    Text[] fragments = highlight.fragments();  
    String fragmentString = fragments[0].string();
}

highlightBuilder.preTags("<span class=\"bg-danger text-white\">");
highlightBuilder.postTags("</span>");