# Pattern Analyzer（模式分析器）

pattern analyzer 使用正则表达式将文本拆分为词语。 正则表达式应该不是**token**本身匹配 **token separators**。 正则表达式默认为`\ W +`（或所有非字符字符）。

> ## B**eware of Pathological 正则表达式**
>
> pattern analyzer 使用java正则表达式
>
> 一个严重的正则表达式可能会运行得非常慢，甚至会抛出一个StackOverflowError，并导致它正在运行的节点突然退出。
>
> 阅读更多关于pathological正则表达式和如何避免它们。

## **定义**

它包括：

Tokenizer(分词器)

* [Pattern Tokenizer](https://www.elastic.co/guide/en/elasticsearch/reference/5.3/analysis-pattern-tokenizer.html) 模式分词器

Token filters(词语过滤器)

* [Lower Case Token Filter](https://www.elastic.co/guide/en/elasticsearch/reference/5.3/analysis-lowercase-tokenfilter.html) 小写过滤器
* [Stop Token Filter](https://www.elastic.co/guide/en/elasticsearch/reference/5.3/analysis-stop-tokenfilter.html)  停用词过滤器 (默认禁用)

## **输出实例**

```
POST _analyze
{
  "analyzer": "pattern",
  "text": "The 2 QUICK Brown-Foxes jumped over the lazy dog's bone."
}
```

上述的句子将产生以下的词语：

```
[ the, 2, quick, brown, foxes, jumped, over, the, lazy, dog, s, bone ]
```

## **配置**

pattern analyzer 接受以下参数：

| pattern         | Java正则表达式默认为`\ W +`。                                    |
| --------------- | ------------------------------------------------------- |
| flags           | Java正则表达式标志。 标志应分开管道，例如“CASE\_INSENSITIVE \| COMMENTS”。 |
| lowercase       | 是否应该降低条件？ 默认为true。                                      |
| stopwords       | 预定义的 stop 词列表，如\_english\_或包含停止词列表的数组。 默认为 \_none\_。    |
| stopwords\_path | 包含停止词的文件的路径。                                            |

有关stop word配置的更多信息，请参阅[Stop Token Filter](https://www.elastic.co/guide/en/elasticsearch/reference/5.2/analysis-stop-tokenfilter.html)


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