Spring's UriComponentsBuilder -- get it encode optional characters is not quite trivial

UriComponentsBuilderEncodingTest.kt

import org.assertj.core.api.Assertions.assertThat
import org.assertj.core.api.Assertions.assertThatExceptionOfType
import org.junit.Test
import org.springframework.web.util.UriComponentsBuilder
import org.springframework.web.util.UriUtils
import java.nio.charset.StandardCharsets.UTF_8

class UrlTests {
    @Test
    fun weakEncode() {
        val uri = UriComponentsBuilder.newInstance()
            .host("server.dev")
            .queryParam("date", "12:35+01:00")
            .queryParam("name", "Süß")
            .build()
            .toUri()
        assertThat(uri.toString()).isEqualTo("//server.dev?date=12:35+01:00&name=Süß")
        assertThat(uri.toASCIIString()).isEqualTo("//server.dev?date=12:35+01:00&name=S%C3%BC%C3%9F")
        // "works", but causes problems when the receiver decides to read '+' as
        // the traditional encoding for ' '.
    }

    @Test
    fun manualEncodeFail() {
        // so, we can try to encode our Date manually, but then ...
        val encodedDate = UriUtils.encode("12:35+01:00", UTF_8)
        val uri = UriComponentsBuilder.newInstance()
            .host("server.dev")
            .queryParam("date", encodedDate)
            .queryParam("name", "Süß")
            .build()
            .toUri()
        // ... it will encode the % sign again and that will definitely not 
        // yield a good reading on the receiver side.
        assertThat(uri.toString()).isEqualTo("//server.dev?date=12%253A35%252B01%253A00&name=Süß")
        assertThat(uri.toASCIIString()).isEqualTo("//server.dev?date=12%253A35%252B01%253A00&name=S%C3%BC%C3%9F")
    }

    @Test
    fun manualEncode() {
        // This solves the above, but now need to encode all parameters manually...
        val encodedDate = UriUtils.encode("12:35+01:00", UTF_8)
        val uri = UriComponentsBuilder.newInstance()
            .host("server.dev")
            .queryParam("date", encodedDate)
            .build(true)
            .toUri()
        assertThat(uri.toString()).isEqualTo("//server.dev?date=12%3A35%2B01%3A00")
        assertThat(uri.toASCIIString()).isEqualTo("//server.dev?date=12%3A35%2B01%3A00")
    }

    @Test
    fun manualEncodeOtherFail() {
        // for example, will fail here:
        val encodedDate = UriUtils.encode("12:35+01:00", UTF_8)
        val uriBuilder = UriComponentsBuilder.newInstance()
            .host("server.dev")
            .queryParam("date", encodedDate)
            .queryParam("name", "Süß")
        assertThatExceptionOfType(IllegalArgumentException::class.java).isThrownBy {
            uriBuilder.build(true)
        }
    }

    @Test
    fun easyEncode() {
        val uri = UriComponentsBuilder.newInstance()
            .host("server.dev")
            .queryParam("date", "12:35+01:00")
            .queryParam("name", "Süß")
            .encode()
            .build()
            .toUri()
        // doesn't solve the problem!
        // Strong encoding does not apply to parameters passed via 'queryParam'.
        assertThat(uri.toString()).isEqualTo("//server.dev?date=12:35+01:00&name=S%C3%BC%C3%9F")
        assertThat(uri.toASCIIString()).isEqualTo("//server.dev?date=12:35+01:00&name=S%C3%BC%C3%9F")
    }

    @Test
    fun useVariables() {
        val uri = UriComponentsBuilder.newInstance()
            .host("server.dev")
            .queryParam("date", "{date}")
            .queryParam("name", "{name}")
            .build()
            .expand(mapOf("date" to "12:35+01:00", "name" to "Süß"))
            .toUri()
        // Also doesn't solve the problem!
        // Strong encoding does not apply to parameters passed via 'queryParam'.
        assertThat(uri.toString()).isEqualTo("//server.dev?date=12:35+01:00&name=Süß")
        assertThat(uri.toASCIIString()).isEqualTo("//server.dev?date=12:35+01:00&name=S%C3%BC%C3%9F")
    }

    @Test
    fun encodeVariables() {
        // this is the only way which does the desired thing!
        // must use 'expand' **and** 'encode'!
        val uri = UriComponentsBuilder.newInstance()
            .host("server.dev")
            .queryParam("date", "{date}")
            .queryParam("name", "{name}")
            .encode()
            .build()
            .expand(mapOf("date" to "12:35+01:00", "name" to "Süß"))
            .toUri()
        assertThat(uri.toString()).isEqualTo("//server.dev?date=12%3A35%2B01%3A00&name=S%C3%BC%C3%9F")
    }

    /*
    Side-note: the difference between toString() and toASCIIString() is not important in our case.
    Ascii-String will always be used for making the actual HTTP-Requests.
    toString() is just for information and is different from the "unencoded" form as you can see from 
    % being encoded again when passed in as a parameter, but not encoded when going from toString() to 
    the Ascii version.
     */
}