phax/ph-cssを使う

// parsing css and get CSSOM
final CascadingStyleSheet css = CSSReader.readFromString(
                ".index h1,
" +
                ".index h2,
" +
                ".index h3,
" +
                ".index h4,
" +
                ".index h5,
" +
                ".index h6 {
" +
                "    font-family: \"ヒラギノ明朝 ProN W3\", \"HiraMinProN-W3\", serif;
" +
                "    font-size: large;
" +
                "}", ECSSVersion.CSS30);

// writing css
final String writtenCss = new CSSWriter(ECSSVersion.CSS30).getCSSAsString(css);