字符过滤器 用于在将字符流传递给 分词器 之前对其进行预处理。

字符过滤器将原始文本作为字符流接收，并可以通过添加、删除或更改字符来转换流。例如，字符过滤器可用于将 印度数字 (٠١٢٣٤٥٦٧٨٩) 转换为 阿拉伯-拉丁数字 (0123456789) ，或从流中去除 HTML 元素<b>。

Elasticsearch 有许多内置的 字符过滤器，可用于构建 自定义分析器。

• HTML 带字符过滤器
html_strip字符过滤器 去除 HTML 元素，例如 <b>。 解码HTML 实体，例如 &。

  GET /_analyze
  {
    "tokenizer": "keyword",
    "char_filter": [
      "html_strip"
    ],
    "text": "<p>I&apos;m so <b>happy</b>!</p>"
  }
  
  [ \nI'm so happy!\n ]
  

  PUT my-index-000001
  {
    "settings": {
      "analysis": {
        "analyzer": {
          "my_analyzer": {
            "tokenizer": "keyword",
            "char_filter": [
              "my_custom_html_strip_char_filter"
            ]
          }
        },
        "char_filter": {
          "my_custom_html_strip_char_filter": {
            "type": "html_strip",
            "escaped_tags": [
              "b"
            ]
          }
        }
      }
    }
  }
  

• 映射字符过滤器
  字符过滤器用指定的mapping替换替换任何出现的指定字符串。

    GET /_analyze
    {
      "tokenizer": "keyword",
      "char_filter": [
        {
          "type": "mapping",
          "mappings": [
            "٠ => 0",
            "١ => 1",
            "٢ => 2",
            "٣ => 3",
            "٤ => 4",
            "٥ => 5",
            "٦ => 6",
            "٧ => 7",
            "٨ => 8",
            "٩ => 9"
          ]
        }
      ],
      "text": "My license plate is ٢٥٠١٥"
    }
  
    [ My license plate is 25015 ]
  

    PUT /my-index-000001
    {
      "settings": {
        "analysis": {
          "analyzer": {
            "my_analyzer": {
              "tokenizer": "standard",
              "char_filter": [
                "my_mappings_char_filter"
              ]
            }
          },
          "char_filter": {
            "my_mappings_char_filter": {
              "type": "mapping",
              "mappings": [
                ":) => _happy_",
                ":( => _sad_"
              ]
            }
          }
        }
      }
    }
  

  GET /my-index-000001/_analyze
  {
    "tokenizer": "keyword",
    "char_filter": [ "my_mappings_char_filter" ],
    "text": "I'm delighted about it :("
  }
  
  [ I'm delighted about it _sad_ ]
  

• 模式替换字符过滤器
  字符过滤器将匹配正则表达式的pattern_replace任何字符替换为指定的替换。

  PUT my-index-000001
  {
    "settings": {
      "analysis": {
        "analyzer": {
          "my_analyzer": {
            "tokenizer": "standard",
            "char_filter": [
              "my_char_filter"
            ]
          }
        },
        "char_filter": {
          "my_char_filter": {
            "type": "pattern_replace",
            "pattern": "(\\d+)-(?=\\d)",
            "replacement": "$1_"
          }
        }
      }
    }
  }
  
  POST my-index-000001/_analyze
  {
    "analyzer": "my_analyzer",
    "text": "My credit card is 123-456-789"
  }
  
  [ My, credit, card, is, 123_456_789 ]