如何将 XSS 过滤后的转义字符还原？

string originalstring = "<script>alert('xss')</script>";
string escapedstring = stringescapeutils.escapehtml4(originalstring);
string unescapedstring = stringescapeutils.unescapehtml4(escapedstring);

@RestControllerAdvice
public class UnescapeResponseBodyAdvice implements ResponseBodyAdvice<Object> {

    @Override
    public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
        return true;
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
                                  Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
        if (body instanceof String) {
            return StringEscapeUtils.unescapeHtml4((String) body);
        }
        return body;
    }
}