如何为 .attr("href") 添加前缀？

Question

I need to add prefix string to my link with is returned by attribute "href".

.getElementsByClass(CLASS_OFFER_NAME)
.firstOrNull()
?.attr("href") // Here need I add prefix to attr href
.orEmpty()

I getting now url eg: work/london/22 but I need add prefix with domain so I want to get www.offerlist.com/work/london/22

Answer 1

May be you can convert String? to Optional<T> and apply prefix concatenation though Optional.map method and finally extract the resulting value using orElse("") ...

This is a functional approach to the problem, but you can obviously solve it via if or ternary or elvis operator applied to the value returned by orEmpty .

If you like the functional approach, you can give a try to this example, which shows both Optional and T? --> Optional use cases:

fun <T> toOptional(value : T?) : Optional<T> {
    if(value == null) {
        return Optional.empty()
    }
    return Optional.of(value)
}

val opt:Optional<String> = Optional.empty()
println(opt.map { x -> "PREFIX/$x" }.orElse(""))
val opt2:Optional<String> = Optional.of("link")
println(opt2.map { x -> "PREFIX/$x" }.orElse(""))
var str : String? = null
println(toOptional(str).map { x -> "PREFIX/$x" }.orElse(""))
var str2  = "hrefValue"
println(toOptional(str2).map { x -> "PREFIX/$x" }.orElse(""))

I hope this can help!