class Spans {
    private static Tracer tracer;

    static {
        Solon.context().getBeanAsync(Tracer.class, bean -> {
            tracer = bean;
        });
    }

    /**
     * 活动中的Span（可能为Null；不推荐用）
     */
    public static Span active() {<FILL_FUNCTION_BODY>}

    /**
     * 活动中的Span
     */
    public static void active(Consumer<Span> consumer) {
        if (tracer != null) {
            consumer.accept(tracer.activeSpan());
        }
    }
}

        if (tracer == null) {
            //避免出现 NullPointerException
            return SpanSimulate.getInstance();
        } else {
            return tracer.activeSpan();
        }
    
<no_super_class>