The image contains a title of the article- Top 50 Java interview questions, and a Java logo as well.
The image contains a title of the article- Top 50 Java interview questions, and a Java logo as well.

Hello, my name is Piotr and I am the author of Codersee- a blog focused on learning Kotlin/Java/Cloud solutions through practical tutorials.

In my previous post, I have created a list of 50 Kotlin interview questions, which in my opinion, everyone should know, before heading to the interview.

This time, I would like to present to you the list of 50 Java interview questions, knowledge of which might increase your chances to get a dream job. …


The image contains a title of the article- Top 50 Kotlin interview questions, and a Kotlin logo as well.
The image contains a title of the article- Top 50 Kotlin interview questions, and a Kotlin logo as well.

This article on Kotlin interview questions has been created as inaugural post for my blog- Codersee.

The main purpose of it’s creation was to help you understand the basic concepts of Kotlin programming language for interview purposes. Whether you are a beginner or a highly experienced developer, core Kotlin plays a very crucial role in any Kotlin-related interview.

Given below you’ll find 50 interview questions with detailed answers which will help you build a solid foundation before you head to the interview.

1. What is Kotlin?

Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference developed by…


1. Introduction

Hello dear readers. In this article, I would like to teach you how to create a Micronaut project with MongoDB and Kotlin.

Micronaut is a modern, JVM-based framework for building modular, easily testable microservice and serverless applications. If you have any prior experience with reflection-based frameworks, like Spring or Spring Boot, you probably noticed that the startup time and memory consumption are bound to the size of the codebase. With Micronaut, these problems have been solved using Java’s annotation processors, making it a really great choice for low memory-footprint environments, like microservices.

Moreover, the creators took a lot of inspiration…


1. Introduction

In today’s article, I would like to walk you step by step through the process of creating a reactive MongoDB REST API CRUD with Spring Boot and Kotlin.

Reactive programming is becoming more and more popular nowadays and plenty of projects incorporated the Spring WebFlux framework, which provides support for creating non-blocking web applications. The reactive approach has plenty of advantages and I personally believe every programmer should know it, at least at a basic level. …


1. Introduction

This time, I would like to show you how to create a simple Spring Boot MongoDB REST API CRUD with Kotlin.

After finishing this article, you will have a fundamental understanding of the process of building Spring Boot applications utilizing Spring Data MongoDB to connect with MongoDB.

2. Run MongoDB Server

Before we start coding, we need to make sure, that our MongoDB server is up and running. In this article, I would like to focus on the Spring Boot part, so we will deploy it as a docker container. …


1. Introduction

Hello and welcome to the second article in a series showing how to secure Spring Boot applications with Keycloak. In the previous tutorial, we’ve learned how to set up the Keycloak server and secure Spring Boot REST API endpoints with it. I highly encourage you to check it out before starting this guide.

In today’s article, I would like to show you how to set up the Keycloak admin client with Spring Boot and Kotlin. I will walk you step by step through the process of setting roles, groups, and users with the Keycloak Admin REST Client.

2. Run Keycloak Server

Just like in…


1. Introduction

In one of my previous articles, I’ve shown you how to create a simple GraphQL Spring Boot project using GraphQL schema files. This time, I would like to teach you another approach- the GraphQL SPQR (GraphQL Schema Publisher & Query Resolver).

To put it simply, GraphQL SPQR dynamically generates a schema from the source code. With this approach, we don’t need to define *.graphqls files anymore, but it will require us to add some additional configuration to the project.

2. Imports

Just like in the previous article, we will start with the imports. …


1. Introduction

Hello and welcome to the first article in a series showing how to use Keycloak with Spring Boot applications.

In this step by step guide, I will show you how to set up a Keycloak server and connect to it using Spring Boot and Kotlin. Additionally, you will learn how to secure REST endpoints with Keycloak combined with the @PreAuthorize annotation.

2. What is Keycloak?

According to the documentation, Keycloak is the Open Source Identity and Access Management solution. In simple terms, it allows us to add authentication and secure our applications with minimum effort. …


1. Introduction

In this step by step tutorial, I would like to show you how to use GraphQL with Spring Boot and Kotlin. Additionally, we will learn how to test with GraphiQL– a dedicated GUI for editing and testing GraphQL queries and mutations.

In simple words, GraphQL is a query language for APIs that provides a more flexible alternative to REST. It allows clients to define the structure of the desired data, and the same structure of the data is returned from the server, therefore preventing large amounts of data from being returned. …


1. Introduction

In one of the previous articles, we’ve learned how to upload CSV files in Spring Boot REST API. I’ve also mentioned, that conversion of CSV files is almost always an important part of any application.

In this guide, I will teach you how to implement Spring Boot CSV export functionality using OpenCSV library and Kotlin.

2. Imports

But before we will start coding, let’s add the necessary dependencies:

implementation("com.opencsv:opencsv:5.2")
implementation("org.springframework.boot:spring-boot-starter-web")

Technically, we do not need web dependency to work with the CSV export, but in this tutorial, I will show you also the two ways in which we can create REST endpoints.

3. Create a User Class

Piotr Wolak

Hi, my name is Piotr and I am the founder of Codersee- a technical blog, where I am teaching programming by practical step by step tutorials.

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