What technologies should java crawlers master?

The technologies to master include: 1. HTTP protocol and network basics; 2. HTML parsing; 3. XPath and CSS selectors; 4. Regular expressions; 5. Network request libraries such as HttpClient or Jsoup; 6. , Cookie and Session management; 7. Multi-threading and asynchronous programming; 8. Anti-crawler and current limiting processing; 9. Database operation; 10. Logging and exception handling; 11. Robot protocol and crawler ethics; 12. Verification code identification, etc. . Detailed introduction: 1. Understand the HTTP protocol and network communication principles

Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Java crawlers involve many aspects of technology. To become a qualified Java crawler engineer, you need to master the following key technologies:

1. HTTP protocol and network basics : Understand the HTTP protocol and network communication principles, including the structure of requests and responses, the meaning of status codes, cookie and session processing, etc.

2. HTML parsing: The crawler needs to be able to parse HTML documents and extract the required information from them. Common HTML parsing libraries include Jsoup, HtmlUnit, etc.

3. XPath and CSS selectors: Understand that XPath and CSS selectors are commonly used methods for selecting elements in crawlers, and can easily locate elements in HTML documents.

4. Regular expressions: Regular expressions are useful in text matching and extraction. For some simple page parsing tasks, regular expressions are an effective tool.

5. Network request libraries such as HttpClient or Jsoup: Use libraries such as HttpClient or Jsoup to make network requests, simulate browser behavior, send HTTP requests, and obtain HTML pages.

6. Cookie and Session Management: Some websites require logging in to obtain data, so they need to be able to handle Cookie and Session and simulate the login state.

7. Multi-threading and asynchronous programming: When processing a large number of pages, multi-threading and asynchronous programming can improve crawling efficiency. Master multi-threaded programming and asynchronous frameworks in Java, such as CompletableFuture, Executor, etc.

8. Anti-crawling and current-limiting processing: Understand common anti-crawling strategies and current-limiting mechanisms, and take corresponding measures to avoid them, such as setting appropriate request headers, using proxy IPs, etc.

9. Database operation: The crawled data usually needs to be stored and managed. Learn to use database operations, such as JDBC, Hibernate, etc.

10. Logging and exception handling: During the crawler process, it is necessary to be able to effectively record logs and handle exceptions to ensure the stability and maintainability of the crawler.

11. Robot protocol and crawler ethics: Comply with the Robot protocol, respect the crawling rules of the website, avoid unnecessary burdens on the website, and maintain good crawler ethics.

12. Verification code identification: Some websites will use verification codes to prevent crawlers. To understand the verification code identification method, you can use a third-party library or implement verification code identification yourself.

These technologies will help you build a powerful, stable, and efficient Java crawler system. In actual applications, depending on the complexity of the specific task, you may need to learn in-depth knowledge in some other fields, such as distributed crawlers, natural language processing, etc.

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