ElasticSearch怎么搜索返回结果的时候，高亮显示关键词

json
{
      "query": {
        "match": {
          "content": "关键词"
        }
      },
      "highlight": {
        "fields": {
          "content": {}
        }
      }
    }

json
{
      "took": 10,
      "hits": {
        "total": 1,
        "max_score": 0.19178301,
        "hits": [
          {
            "_index": "my_index",
            "_type": "my_type",
            "_id": "1",
            "_score": 0.19178301,
            "_source": {
              "content": "这是一篇包含关键词的文章"
            },
            "highlight": {
              "content": [
                "这是一篇包含 \<em\>关键词\</em\> 的文章"
              ]
            }
          }
        ]
      }
    }