获取适用于 Java 中特定 HTML 类的 CSS 规则列表

Question

我正在使用CSS Parser 来获取属于一组 HTML 类的特定 CSS 规则。目前我在网站上有一个 CSS 规则列表，但是我不知道如何获得我正在寻找的规则。

当前代码：

InputSource inputSource = new InputSource("example.com");
CSSOMParser parser = new CSSOMParser(new SACParserCSS3());

ErrorHandler errorHandler = new CSSErrorHandler();
parser.setErrorHandler(errorHandler);

CSSStyleSheet sheet = parser.parseStyleSheet(inputSource, null, null);

CSSRuleList rules = sheet.getCssRules();

我的一个选择是执行 for 循环，但我不愿意这样做，因为
一个。如果一个页面中有数百条规则，它会很慢。
乙。似乎没有获取规则类名的方法。

任何帮助将不胜感激

Answer 1

添加：CSS 已经被您的代码解析，因此您只需要查看在性能方面可能可以接受的选择器。

添加 b：CSSStyleRule 接口缺少方法 getSelectors() 但 CSSStyleRuleImpl 有。所以你可以尝试一下：

scanRules(rules, name -> name.contains("e"), 
    (names, rule) -> System.out.println(
            new TreeSet<>(names) + " --> " + rule.getCssText()));

使用递归辅助方法

// scan CSS rules including rules contained in media rules 
void scanRules(CSSRuleList rules, Predicate<String> classNameTest,
        BiConsumer<Set<String>, CSSStyleRule> ruleAction) {
    for (int ri = 0; ri < rules.getLength(); ri++) {
        CSSRule rule = rules.item(ri);
        if (rule.getType() == CSSRule.MEDIA_RULE) {
            CSSMediaRule mr = (CSSMediaRule) rule;
            scanRules(mr.getCssRules(), classNameTest, ruleAction);
        } else if (rule.getType() == CSSRule.STYLE_RULE) {
            CSSStyleRuleImpl styleRule = (CSSStyleRuleImpl) rule;
            SelectorList selectors = styleRule.getSelectors();
            // if (!styleRule.getSelectorText().contains(".name"))
            //  continue; // selector text test might cause speed up...
            for (int si = 0; si < selectors.getLength(); si++) {
                Selector selector = selectors.item(si);
                Set<String> classNames = classNamesInSelectorMatching(selector, classNameTest);
                if (!classNames.isEmpty()) 
                    ruleAction.accept(classNames, styleRule);
            }
        }
    }
}

// find matching class names in given (potentially complex) selector
Set<String> classNamesInSelectorMatching(Selector selector,
        Predicate<String> nameMatches) {
    switch (selector.getSelectorType()) {
        case Selector.SAC_CHILD_SELECTOR:
        case Selector.SAC_DESCENDANT_SELECTOR:
        case Selector.SAC_DIRECT_ADJACENT_SELECTOR: {
            DescendantSelector ds = (DescendantSelector) selector;
            Set<String> set = new HashSet<>();
            set.addAll(classNamesInSelectorMatching(ds.getAncestorSelector(), nameMatches));
            set.addAll(classNamesInSelectorMatching(ds.getSimpleSelector(), nameMatches));
            return set;
        }
        case Selector.SAC_NEGATIVE_SELECTOR: {
            NegativeSelector ns = (NegativeSelector) selector;
            return classNamesInSelectorMatching(ns.getSimpleSelector(), nameMatches);
        }
        case Selector.SAC_CONDITIONAL_SELECTOR: {
            ConditionalSelector ns = (ConditionalSelector) selector;
            return classNamesInConditionMatching(ns.getCondition(), nameMatches);
        }
        default:
            return Collections.emptySet();
    }
}

// find matching class names in given (potentially complex) condition
Set<String> classNamesInConditionMatching(Condition condition,
        Predicate<String> nameMatches) {
    switch (condition.getConditionType()) {
        case Condition.SAC_CLASS_CONDITION: {
            AttributeCondition ac = (AttributeCondition) condition;
            if (nameMatches.test(ac.getValue()))
                return Collections.singleton(ac.getValue());
            else
                return Collections.emptySet();
        }
        case Condition.SAC_AND_CONDITION:
        case Condition.SAC_OR_CONDITION: {
            CombinatorCondition cc = (CombinatorCondition) condition;
            Set<String> set = new HashSet<>();
            set.addAll(classNamesInConditionMatching(cc.getFirstCondition(), nameMatches));
            set.addAll(classNamesInConditionMatching(cc.getSecondCondition(), nameMatches));
            return set;
        }
        case Condition.SAC_NEGATIVE_CONDITION: {
            NegativeCondition nc = (NegativeCondition) condition;
            return classNamesInConditionMatching(nc.getCondition(), nameMatches);
        }
        default:
            return Collections.emptySet();
    }
}

我已经尝试过输入 https://www.w3.org/2008/site/css/minimum-src.css，它似乎对我有用。