How do Java regular expressions efficiently extract specific URLs in HTML text?

Java regular expressions efficiently extract HTML URLs: a practical guide

This article will demonstrate how to extract specific URLs from HTML text using Java regular expressions. We will use an example to illustrate how to accomplish this task efficiently.

Question: Extract all URLs starting with "www." and ending with ".com" or ".cn" from HTML text.

Sample HTML (including URL):

<a>www.baidu.com</a> <a>www.qq.com</a> <a>www.aaa.cn</a> www.eee.cn

Java code and regular expressions:

We use the regular expression www\.\w (\.com|\.cn) to match the URL. \w matches one or more alphanumeric characters, \. matches dot numbers (requires escape), ( ) is used to group match ".com" or ".cn".

String html = " <a>www.baidu.com</a> <a>www.qq.com</a> <a>www.aaa.cn</a> www.eee.cn";
String reg = "www\\.\\w (\\.com|\\.cn)"; // Note that you need to escape the backslash Pattern pattern = Pattern.compile(reg, Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(html);

while (matcher.find()) {
    System.out.println(matcher.group());
}

Running results:

<code>www.baidu.com www.qq.com www.aaa.cn www.eee.cn</code>

Code description:

1. Pattern.compile(reg, Pattern.CASE_INSENSITIVE) : Compile regular expressions, the CASE_INSENSITIVE flag makes the match case-insensitive.
2. pattern.matcher(html) : Creates a Matcher object to find matches in HTML text.
3. matcher.find() : Find the next match.
4. matcher.group() : Returns the matching substring.

Important tips:

For complex HTML structures, parsing using regular expressions may not be reliable enough and errors are prone to occur. For more complex HTML parsing, it is recommended to use a professional HTML parser library, such as Jsoup, to ensure parsing accuracy and stability. This example is only used to demonstrate the basic usage of regular expressions.

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