Crawler4j

Extending the WebCrawler class allows setup in minutes, as shown in the quickstart example with minimal boilerplate code for URL filtering and page processing.

Built-in politeness delays prevent server overload, with adjustable settings like setPolitenessDelay() to balance crawling speed and ethical behavior.

Supports interrupted crawls to be resumed via setResumableCrawling(true), useful for long-running tasks, though it may slightly reduce performance.

Automatically respects robots.txt rules through RobotstxtServer, ensuring ethical crawling out of the box without extra implementation.