Pattern Replace Character Filter使用正则表达式来匹配应替换为指定替换字符串的字符。替换字符串可以引用正则表达式中的捕获组。
小心"病态"正则表达式
Pattern Replace Character Filter使用Java正则表达式。
一个“病态”的正则表达式可能会运行得非常慢，甚至会抛出一个StackOverflowError，还会导致其运行的节点突然退出。
更多信息请查看pathological regular expressions and how to avoid them.
配置
Pattern Replace Character Filter会接收以下参数：
在下面例子中，我们使用Pattern Replace Character Filter实现用下划线替代任何嵌入的破折号，即123-456-789→123_456_789：
PUT my_index
{
"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/_analyze
{
"analyzer": "my_analyzer",
"text": "My credit card is 123-456-789"
}
上面案例将返回如下结果：
[ My, credit, card, is 123_456_789 ]
出于搜索目的使用替换字符串，会引起原始文本长度的更改，进而导致不正确的高亮显示。案例如下所示。
这个示例在遇到小写字母后跟大写字母（即fooBarBaz→foo Bar Baz）时插入空格，允许单独查询camelCase字词：
PUT my_index
{
"settings": {
"analysis": {
"analyzer": {
"my_analyzer": {
"tokenizer": "standard",
"char_filter": [
"my_char_filter"
],
"filter": [
"lowercase"
]
}
},
"char_filter": {
"my_char_filter": {
"type": "pattern_replace",
"pattern": "(?<=\\p{Lower})(?=\\p{Upper})",
"replacement": " "
}
}
}
},
"mappings": {
"my_type": {
"properties": {
"text": {
"type": "text",
"analyzer": "my_analyzer"
}
}
}
}
}
POST my_index/_analyze
{
"analyzer": "my_analyzer",
"text": "The fooBarBaz method"
}
示例返回的结果如下：
[ the, foo, bar, baz, method ]
查询bar可以正确找到文档，但突出显示结果将产生不正确的高光，因为我们的字符过滤器更改了原始文本的长度：
PUT my_index/my_doc/1?refresh
{
"text": "The fooBarBaz method"
}
GET my_index/_search
{
"query": {
"match": {
"text": "bar"
}
},
"highlight": {
"fields": {
"text": {}
}
}
}
以上的输出结果是：
{
"timed_out": false,
"took": $body.took,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 0.2824934,
"hits": [
{
"_index": "my_index",
"_type": "my_doc",
"_id": "1",
"_score": 0.2824934,
"_source": {
"text": "The fooBarBaz method"
},
"highlight": {
"text": [
"The foo<em>Ba</em>rBaz method"
]
}
}
]
}
}