Utility method to convert HTML text to plain text while preserving newlines (using jsoup as main dependency)

HtmlToTextUtils.java

import org.apache.commons.lang3.StringUtils;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.nodes.Node;
import org.jsoup.nodes.TextNode;

import java.util.List;
import java.util.stream.Collectors;

public final class HtmlToTextUtils {

    public static String htmlToTextWhilePreservingNewlines(String htmlText) {
        final Document document = Jsoup.parse(StringUtils.trimToEmpty(htmlText));

        String plainText = buildTextFromNodeWhilePreservingNewlines(document.body()).toString().trim();

        plainText = plainText.replaceAll(" +", " ");

        plainText = plainText.lines().map(String::trim).collect(Collectors.joining("\n"));

        plainText = plainText.replaceAll("\n{2,}", "\n\n");

        return plainText;
    }

    private static StringBuilder buildTextFromNodeWhilePreservingNewlines(Node node) {
        final StringBuilder stringBuilder = new StringBuilder();

        if (node instanceof TextNode) {
            TextNode textNode = (TextNode) node;
            stringBuilder.append(textNode.text());
        }

        for (Node childNode : node.childNodes()) {
            stringBuilder.append(buildTextFromNodeWhilePreservingNewlines(childNode));
        }

        if (node instanceof Element) {
            final String tagName = ((Element) node).tagName();
            if (List.of("p", "br", "li", "h1", "h2", "h3", "h4", "h5", "h6").contains(tagName)) {
                stringBuilder.append("\n");
            }
        }

        return stringBuilder;
    }

}

HtmlToTextUtilsTests.java

import org.junit.jupiter.api.Test;

import static org.assertj.core.api.Assertions.assertThat;

class HtmlToTextUtilsTests {

    @Test
    void shouldCleanHtmlToTextWhilePreservingNewlines() {
        final String html = "<h5>Description</h5><ul><li>%100 cotton</li><li>Flat pattern</li></ul><p><br></p><p><br></p><h5>Model Information</h5><p><strong>Chest:</strong> 90cm <strong>Waist:</strong> 60cm <strong>Width:</strong> 90cm <strong>Length:</strong> 180cm </p><p> The model is wearing <strong>L</strong> sized product.</p>";

        assertThat(HtmlToTextUtils.htmlToTextWhilePreservingNewlines(html))
                .isEqualTo("Description\n" +
                        "%100 cotton\n" +
                        "Flat pattern\n" +
                        "\n" +
                        "Model Information\n" +
                        "Chest: 90cm Waist: 60cm Width: 90cm Length: 180cm\n" +
                        "The model is wearing L sized product.");
    }

    @Test
    void shouldCleanHtmlToTextWhilePreservingNewlinesWhenNullHtml() {
        final String html = null;

        assertThat(HtmlToTextUtils.htmlToTextWhilePreservingNewlines(html)).isEqualTo("");
    }

    @Test
    void shouldCleanHtmlToTextWhilePreservingNewlinesWhenEmptyHtml() {
        final String html = "";

        assertThat(HtmlToTextUtils.htmlToTextWhilePreservingNewlines(html)).isEqualTo("");
    }

    @Test
    void shouldCleanHtmlToTextWhilePreservingNewlinesWhenBlankHtml() {
        final String html = " ";

        assertThat(HtmlToTextUtils.htmlToTextWhilePreservingNewlines(html)).isEqualTo("");
    }

    @Test
    void shouldCleanHtmlToTextWhilePreservingNewlinesWhenInvalidHtml() {
        final String html = "<p>invalid<br>tags<p>";

        assertThat(HtmlToTextUtils.htmlToTextWhilePreservingNewlines(html))
                .isEqualTo("invalid\n" +
                        "tags");
    }

}