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License: MIT License

Kotlin 97.11% Java 2.60% HTML 0.29%

kotlin-tutorials's Introduction

Kotlin Tutorials

This project is a collection of small and focused tutorials - each covering a single and well defined area of development in the Kotlin ecosystem. All the tutorials can be found on https://www.baeldung.com/kotlin

Building the project

To build the entire repository with only Unit Tests enabled run:

mvn clean install -Pdefault

or if we want to build the entire repository with Integration Tests enabled, we can do:

mvn clean install -Pintegration

This should not be needed often as we are usually concerned with a specific module.

Building a single module

To build a specific module run the command: mvn clean install in the module directory.

Working with the IDE

This repo contains a large number of modules. When you're working with an individual module, there's no need to import all of them (or build all of them) - you can simply import that particular module in either Eclipse or IntelliJ.

Running Tests

The command mvn clean install from within a module will run the unit tests in that module. For Spring modules this will also run the SpringContextTest if present.

To run the integration tests, use the command:

mvn clean install -Pintegration

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kotlin-tutorials's Issues

JacksonUnitTest.kt very fragile, hard/impossible to get working

Reported in FasterXML/jackson-module-kotlin#437

I have been trying to reproduce examples in https://github.com/Baeldung/kotlin-tutorials/blob/master/kotlin-libraries-2/src/test/kotlin/com/baeldung/kotlin/jackson/JacksonUnitTest.kt

In particular, when compiling under Gradle/IntelliJ the Kotlin compiler rejects the syntax used

import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.kotlin.KotlinModule
. . .
val mapper = jacksonObjectMapper()
. . .
data class KmsCmkSecret(val cmkIdentifier: String, val dataKeyCiphertext: String)
. . .
val kmsCmkSecret1 = mapper.readValue<KmsCmkSecret>(secretJson)
val kmsCmkSecret2: KmsCmkSecret = mapper.readValue(secretJson)

kmsCmkSecret1

e: /Users/ekolotyluk/dev/crypto/common/src/main/kotlin/com/fispan/crypto/Aws.kt: (87, 35): None of the following functions can be called with the arguments supplied: 
public inline fun <reified T> ObjectMapper.readValue(jp: JsonParser): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: File): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: InputStream): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: Reader): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: URL): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: ByteArray): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(content: String): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin

kmsCmkSecret2

e: /Users/ekolotyluk/dev/crypto/common/src/main/kotlin/com/fispan/crypto/Aws.kt: (88, 51): None of the following functions can be called with the arguments supplied: 
public inline fun <reified T> ObjectMapper.readValue(jp: JsonParser): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: File): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: InputStream): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: Reader): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: URL): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(src: ByteArray): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin
public inline fun <reified T> ObjectMapper.readValue(content: String): TypeVariable(T) defined in com.fasterxml.jackson.module.kotlin

Interestingly enough, in my code if I use

val kmsCmkSecret = mapper.readValue(secretJson, KmsCmkSecret::class.java)

this does not fail. In my build.gradle I am using

    implementation("com.fasterxml.jackson.module:jackson-module-kotlin:latest.release")

I am using kotlin_version = "1.5.0-RC"

I've already wasted many hours fussing around with this, and this is very frustrating because the experience does not at all follow the simplicity of the examples. It seems the entire mechanism is very fragile and unpredictable... Having used Jackson for many years with success, I am astonished at this difficulty...

As an aside, I have completely given up on Kotlin Serialization, as it is even more pathological...

I may be reporting this in the wrong place, but it's where I started...

Kotlin Sealed Class is package level now

Hey, I think this line is wrong as Kotlin allows for package-level inheritance now.

The compiler guarantees that only classes defined in the same source file as the sealed class are able to inherit from it

Flow is intended to return a single value that changes over time, not as a replacement of list.

The Kotlin Flow concept is intended to return a reference that notifies observers of changes to its value (which may be a list/collection) but here it is used as a replacement for list. It will kind of work but the way to return a list as flow is Flow<List<T>>.

There is no example usage of the config

A sample class which uses constructor injection of the config should be provided to show how to use it

Which license governs the kotlin-tutorials?

Hi Team,

May you please advise which license governs the kotlin-tutorials repo/project?

Thanks,
Radi

Guide to Spring Boot Testing

Hey @SmartyAnsh,

Thanks for the great article about Spring Boot Testing. I am working with gradle / kotlin setup and could not get your test setup working. I always got the error:

kotlin.UninitializedPropertyAccessException: lateinit property mockMvc has not been initialized

I don't know if this is just gradle specific, but in order to get kotest / funspec working with spring boot, I had to add:

override fun extensions() = listOf(io.kotest.extensions.spring.SpringExtension)

to my test. Than everything worked. Here is my demo controller test as an example:

@WebMvcTest
@ContextConfiguration
class DemoControllerTest : FunSpec() {
    override fun extensions() = listOf(io.kotest.extensions.spring.SpringExtension)

    @Autowired
    private lateinit var mockMvc: MockMvc

    init {
        test("index") {
            mockMvc.get("/hello").andReturn().response.contentAsString shouldBe "hello"
        }
    }
}

Person entity default constructor

I see that in your example for JPA the person object is created using an ID of 0. I thought that with the jpa plugin we can create person using no-arg constructor Person() and then set the other properties except for ID. Please clarify if providing default ID's at object creation time is the only way to work with Kotlin & JPA?

Current implementation of LoggingResponseDecorator may log uninitialized headers

During instantiation of the LoggingResponseDecorator, you are logging the headers of the response.

kotlin-tutorials/spring-reactive-kotlin/src/main/kotlin/com/baeldung/logfilter/decorator/LoggingResponseDecorator.kt

Line 29 in 5368ede

log.debug("{}", delegate.headers.asString())

At that point the headers may not be initialized or fully committed. Besides, if I wanted to log the status code of the response, that would also be undefined at that stage. I have only tested this on the Java version of this code, but invoking the beforeCommit delegate method worked for me:

public LoggingResponseDecorator(ServerHttpResponse delegate) {
    super(delegate);
    beforeCommit(() -> Mono.fromRunnable(() -> {
        if (log.isDebugEnabled()) {
            log.debug("{} {}", getStatusCode(), getHeaders());
        }
    }));
}

Sorry to create an issue of this, but the blog entry has the comments disabled.