Fess is very powerful and easily deployable Enterprise Search Server.

Norconex Importer is a Java library and command-line application meant to "parse" and "extract" content out of a file as plain text, whatever its format (HTML, PDF, Word, etc). In addition, it allows you to perform any manipulation on the extracted text before using it in your own service or application.

Easy to use lightweight web crawler（易用的轻量化网络爬虫）

A set of reusable Java components that implement functionality common to any web crawler

Norconex HTTP Collector is a flexible web crawler for collecting, parsing, and manipulating data from the Internet (or Intranet) to various data repositories such as search engines.

An HTTP+HTTP/2 client for Android and Java applications.