Kotlin String url params

Question

I have a string url like this:

exampleUrl = www.example.com/test?item=param1=1&param2=11&param3=111&item=param1=2&param2=22&param3=222

and i want to extract from it a Map of key values using item as key.

I wrote the below function

fun String.getUrlParams(): Map<String, List<String>> {
    val params = HashMap<String, List<String>>()
    val urlParts = this.split("\\?".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
    if (urlParts.size > 1) {
        val query = urlParts[1]
        for (param in query.split("item=".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()) {
            System.out.println(param)
            val key = "item"
            var value = URLDecoder.decode(param, "UTF-8")
            var values: MutableList<String>? = params[key] as MutableList<String>?
            if (values == null) {
                values = ArrayList()
                params[key] = values as ArrayList<String>
            }
            values?.add(value)
        }

    }
    return params
}

But on printed data i am getting this -> {item=[, param1=1&param2=11&param3=111&, param1=2&param2=22&param3=222]}. It has an empty value on start and the & symbol on the end of second value.

The correct one should be -> {item=[param1=1&param2=11&param3=111, param1=2&param2=22&param3=222]}

What am i missing? Thanks in advance

Tenfour04 · Accepted Answer · 2021-02-18 15:59:13Z

Splitting on something that appears right at the start or end of a String will give you an empty String at the start or end of the results.

Instead of dropLastWhile you can filter all empty Strings.

You can use "&?item=" to avoid having the trailing & in your first block.

After removing the unnecessary toTypedArray() and Java-specific code you have:

fun String.getUrlParams(): Map<String, List<String>> {
    val params = HashMap<String, List<String>>()
    val urlParts = split("\\?".toRegex()).filter(String::isNotEmpty)
    if (urlParts.size > 1) {
        val query = urlParts[1]
        for (param in query.split("&?item=".toRegex()).filter(String::isNotEmpty)) {
            val key = "item"
            val value = URLDecoder.decode(param, "UTF-8")
            var values: MutableList<String>? = params[key] as MutableList<String>?
            if (values == null) {
                values = ArrayList()
                params[key] = values
            }
            values.add(value)
        }
    }
    return params
}

Cleaning it up a bit gives:

fun String.getUrlParams(): Map<String, List<String>> {
    val urlParts = split("\\?".toRegex()).filter(String::isNotEmpty)
    if (urlParts.size < 2) {
        return emptyMap()
    }
    val query = urlParts[1]
    return listOf("item").associateWith { key ->
        query.split("&?$key=".toRegex()).filter(String::isNotEmpty)
            .map { URLDecoder.decode(it, "UTF-8") }
    }
}

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