Java中富文本转markdown

实现富文本即html语法转md，要求是尽可能展示效果一样，可以有少许误差，另外只实现了html中的body转md，其他标签如head等未实现。

大致思路是：通过jsoup工具获取html节点，再穷举替换。前提是熟悉html以及md语法

依赖如下：

        <dependency>
            <groupId>org.jsoup</groupId>
            <artifactId>jsoup</artifactId>
            <version>1.16.1</version>
        </dependency>

代码如下：

import lombok.Data;
import org.apache.commons.lang3.StringUtils;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import java.util.ArrayList;
import java.util.List;

public class Html2MarkdownUtil {

    public static void main(String[] args) {
        String html = "<p style=\"padding: 0; margin: 10px 0; line-height: 1.5; font-size: 16px;\"><b style=\"padding: 0; margin: 0;\">Hello<font color=\"#c24f4a\" style=\"padding: 0; margin: 0;\">world</font></b></p>";
        System.out.println(parseHtml2Markdown(html));
    }

    /**
     * 解析html2md
     *
     * @param html html
     * @return {@link String}
     */
    public static String parseHtml2Markdown(String html) {
        Document doc = Jsoup.parse(html);
        StringBuilder sb = new StringBuilder();
        for (Element element : doc.body().children()) {
            HtmlElement htmlElement = new HtmlElement(element);
            sb.append(htmlElement.getMarkdownText());
        }
        return sb.toString();
    }

    /**
     * 标记文本
     *
     * @param element 要素
     * @return {@link String}
     */
    public static String toMarkdownText(Element element) {
        StringBuilder sb = new StringBuilder();
        String tagName = element.tagName().toLowerCase();
        String text = element.ownText();
        switch (tagName) {
            case "h1":
                sb.append("# ").append(text);
                break;
            case "h2":
                sb.append("## ").append(text);
                break;
            case "h3":
                sb.append("### ").append(text);
                break;
            case "h4":
                sb.append("#### ").append(text);
                break;
            case "h5":
                sb.append("##### ").append(text);
                break;
            case "h6":
                sb.append("###### ").append(text);
                break;
            case "p":
            case "font":
            case "b":
            case "span":
                sb.append(text);
                break;
            case "ul":
                for (Element child : element.children()) {
                    sb.append("* ").append(child.text().trim()).append("\n");
                }
                break;
            case "ol":
                int index = 1;
                for (Element child : element.children()) {
                    sb.append(index).append(". ").append(child.text().trim()).append("\n");
                    index++;
                }
                break;
            case "a":
                sb.append("[").append(text).append("](").append(element.attr("href")).append(")");
                break;
            case "strong":
                sb.append("**").append(text).append("**");
                break;
            case "em":
                sb.append("_").append(text).append("_");
                break;
            case "blockquote":
                sb.append("> ").append(text);
                break;
            case "img":
                sb.append("![");
                if (element.hasAttr("alt")) {
                    sb.append(element.attr("alt"));
                }
                sb.append("](").append(element.attr("src")).append(")");
                break;
            default:
                break;
        }
        return sb.toString();
    }

    @Data
    public static class HtmlElement {

        private Element element;
        private String tagName;
        private String ownText;
        private boolean isNewline;
        private List<HtmlElement> children;

        public HtmlElement(Element element) {
            this.element = element;
            this.tagName = element.tagName().toLowerCase();
            this.ownText = element.ownText();
            this.isNewline = isNewline();
            if (!StringUtils.equalsAny(this.tagName, "ul", "ol")) {
                Elements children = element.children();
                if (children.size() > 0) {
                    this.children = new ArrayList<>();
                    for (Element child : children) {
                        this.children.add(new HtmlElement(child));
                    }
                }
            }
        }

        public boolean isNewline() {
            return StringUtils.equalsAny(tagName, "h1", "h2", "h3", "h4", "h5", "h6", "p", "ul", "ol", "blockquote");
        }

        public String getMarkdownText() {
            StringBuilder sb = new StringBuilder();
            sb.append(toMarkdownText(element));
            if (children != null && children.size() > 0) {
                for (HtmlElement child : children) {
                    sb.append(child.getMarkdownText());
                }
            }
            if (isNewline) {
                sb.append("\n");
            }
            return sb.toString();
        }
    }
}