ElasticSearch自定义分析器-集成结巴分词插件

关于结巴分词 ElasticSearch 插件：

https://github.com/huaban/elasticsearch-analysis-jieba

该插件由huaban开发。支持Elastic Search 版本<=2.3.5。

结巴分词分析器

结巴分词插件提供3个分析器：jieba_index、jieba_search和jieba_other。

1. jieba_index: 用于索引分词，分词粒度较细；
2. jieba_search: 用于查询分词，分词粒度较粗；
3. jieba_other: 全角转半角、大写转小写、字符分词；

使用jieba_index或jieba_search分析器，能够实现基本的分词效果。

如下是最小配置示例：

{
    "mappings": {
        "test": {
            "_all": {
                "enabled": false
            },
            "properties": {
                "name": {
                    "type": "string",
                    "analyzer": "jieba_index",
                    "search_analyzer": "jieba_index"
                }
            }
        }
    }
}

在生产化境中，由于业务的须要，须要考虑实现如下功能：

1. 支持同义词；
2. 支持字符过滤器；

结巴插件提供的分析器jieba_index、jieba_search没法实现以上功能。

自定义分析器

当jieba_index、jieba_search分析器不知足生成环境的需求时，咱们能够使用自定义分析器来解决以上问题。

分析器是由字符过滤器，分词器，词元过滤器组成的。

一个分词器容许包含多个字符过滤器+一个分词器+多个词元过滤器。

因业务的需求，咱们须要使用映射字符过滤器来实现分词前某些字符串的替换操做。如将用户输入的c#替换为csharp，c++替换为cplus。

下面逐一介绍分析器各个组成部分。

1. 映射字符过滤器Mapping Char Filter

这个是Elastic Search内置的映射字符过滤器，位于settings –> analysis -> char_filter下：

PUT /my_index
{
    "settings": {
        "analysis": {
            "char_filter": {
                "mapping_filter": {
                    "type": "mapping",
                    "mappings": [
                      "c# => csharp",
                      "c++ => cplus"
                  ]
                }
            }
        }
    }
}

也能够经过文件载入字符映射表。

PUT /my_index
{
    "settings": {
        "analysis": {
            "char_filter": {
                "mapping_filter": {
                    "type": "mapping",
                    "mappings_path": "mappings.txt"
                }
            }
        }
    }
}

文件默认存放config目录下，即config/ mappings.txt。

2. 结巴分词词元过滤器JiebaTokenFilter

JiebaTokenFilter接受一个SegMode参数，该参数有两个可选值：Index和Search。

咱们预先定义两个词元过滤器：jieba_index_filter和jieba_search_filter。

PUT /my_index
{
    "settings": {
        "analysis": {
            "filter": {
                "jieba_index_filter": {
                    "type": "jieba",
                    "seg_mode": "index"
                },
                "jieba_search_filter": {
                    "type": "jieba",
                    "seg_mode": "search"
                }
            }
        }
    }
}

 这两个词元过滤器将分别用于索引分析器和查询分析器。

3. stop 停用词词元过滤器

因分词词元过滤器JiebaTokenFilter并不处理停用词。所以咱们在自定义分析器时，须要定义停用词词元过滤器来处理停用词。 

Elastic Search提供了停用词词元过滤器，咱们能够这样来定义：

PUT /my_index
{
    "settings": {
        "analysis": {
            "filter": {
                "stop_filter": {
                    "type":       "stop",
                    "stopwords": ["and", "is", "the"]
                }
            }
        }
    }
}

也能够经过文件载入停用词列表 

PUT /my_index
{
    "settings": {
        "analysis": {
            "filter": {
                "stop_filter": {
                    "type": "stop",
                    "stopwords_path": "stopwords.txt"
                }
            }
        }
    }
}

文件默认存放config目录下，即config/ stopwords.txt。

4. synonym 同义词词元过滤器

咱们使用ElasticSearch内置同义词词元过滤器来实现同义词的功能。

PUT /my_index
{
    "settings": {
        "analysis": {
            "filter": {
                "synonym_filter": {
                    "type": "synonym",
                    "stopwords": [
                      "中文,汉语,汉字"
                  ]
                }
            }
        }
    }
}

若是同义词量比较大时，推荐使用文件的方式载入同义词库。

PUT /my_index
{
    "settings": {
        "analysis": {
            "filter": {
                "synonym_filter ": {
                    "type": "synonym",
                    "stopwords_path": "synonyms.txt"
                }
            }
        }
    }
}

5. 从新定义分析器jieba_index和jieba_search

Elastic Search支持多级分词，咱们使用whitespace分词做为分词器；并在词元过滤器加入定义好的Jiebie分词词元过滤器：jieba_index_filter和jieba_search_filter。 

PUT /my_index
{
    "settings": {
        "analysis": {
            "analyzer": {
                "jieba_index": {
                    "char_filter": [
                      "mapping_filter"
                  ],
                    "tokenizer": "whitespace",
                    "filter": [
                      "jieba_index_filter",
                      "stop_filter",
                      "synonym_filter"
                  ]
                },
                "jieba_search": {
                    "char_filter": [
                      "mapping_filter"
                  ],
                    "tokenizer": "whitespace",
                    "filter": [
                      "jieba_search_filter",
                      "stop_filter",
                      "synonym_filter"
                  ]
                }
            }
        }
    }
}

注意，上面分析器的命名依然使用jieba_index和jieba_search，以便覆盖结巴分词插件提供的分析器。

当存在多个同名的分析器时，Elastic Search会优先使用索引配置中定义的分析器。

这样在代码调用层面便无需再更改。 

下面是完整的配置：

PUT /my_index
{
    "settings": {
        "analysis": {
            "char_filter": {
                "mapping_filter": {
                    "type": "mapping",
                  "mappings_path": "mappings.txt"
                }
            }
            "filter": {
                "synonym_filter ": {
                    "type": "synonym",
                    "stopwords_path": "synonyms.txt"
                },
                "stop_filter": {
                    "type": "stop",
                    "stopwords_path": "stopwords.txt"
                },
                "jieba_index_filter": {
                    "type": "jieba",
                    "seg_mode": "index"
                },
                "jieba_search_filter": {
                    "type": "jieba",
                    "seg_mode": "search"
                }
            }
            "analyzer": {
                "jieba_index": {
                    "char_filter": [
                      "mapping_filter"
                  ],
                    "tokenizer": "whitespace",
                    "filter": [
                      "jieba_index_filter",
                      "stop_filter",
                      "synonym_filter"
                  ]
                },
                "jieba_search": {
                    "char_filter": [
                      "mapping_filter"
                  ],
                    "tokenizer": "whitespace",
                    "filter": [
                      "jieba_search_filter",
                      "stop_filter",
                      "synonym_filter"
                  ]
                }
            }
        }
    }
}

 参考资料：

https://www.elastic.co/guide/en/elasticsearch/reference/2.3/index.html

http://www.tuicool.com/articles/eUJJ3qF