Character filters are used to preprocess the stream of characters before it is passed to the tokenizer.
A character filter receives the original text as a stream of characters and
can transform the stream by adding, removing, or changing characters. For
instance, a character filter could be used to convert Hindu-Arabic numerals
(٠١٢٣٤٥٦٧٨٩) into their Arabic-Latin equivalents (0123456789), or to strip HTML
<b> from the stream.
Elasticsearch has a number of built in character filters which can be used to build custom analyzers.
- HTML Strip Character Filter
html_stripcharacter filter strips out HTML elements like
<b>and decodes HTML entities like
- Mapping Character Filter
mappingcharacter filter replaces any occurrences of the specified strings with the specified replacements.
- Pattern Replace Character Filter
pattern_replacecharacter filter replaces any characters matching a regular expression with the specified replacement.