Kotlin

Kotlin + Spring Boot CRUD examples:

Kotlin + Spring Boot with Template Engines CRUD examples:

Build REST APIs with Kotlin + Spring Boot:


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Learn Java 8 streams with an example - print odd/even numbers from Array and List

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Example 1: Java 8 program to print odd numbers from a List import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; /*Java 8 Program to find Odd Numbers from a List*/ public class DriverClass { public static void main( String [] args) { List < Integer > numbers = Arrays. asList( 1 , 4 , 8 , 40 , 11 , 22 , 33 , 99 ); List < Integer > oddNumbers = numbers.stream(). filter(o -> o % 2 != 0 ). collect(Collectors.toList()); System.out.println(oddNumbers); } } Spring Boot + Angular 10 + Mongo DB CRUD Example - click here Example 2: Java 8 program to print even numbers from a List import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; /*Java 8 Program to find Even Numbers from a List*/ public class DriverClass { public static void main( String [] args) { List &l
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Spring Boot + Mockito simple application with 100% code coverage

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In this article, we will show you a simple  Spring Boot example to demonstrate test methods for Controllers, Service, and Repository, And code coverage analysis using the EclEmma plugin. Technologies used: Spring Boot 2.6.4 Mockito 3.11.2 Maven 3+ EclEmma plugin Junit 5 Java 17 A quick overview of  Spring Boot, Mockito, and EclEmma plugin Spring boot: Spring boot to develop REST web services and microservices. Spring Boot has taken the Spring framework to the next level. It has drastically reduced the configuration and setup time required for spring projects. We can set up a project with almost zero configuration and start building the things that actually matter to your application. Mockito: Mockito is a mocking framework, a JAVA-predicated library that is utilized for efficacious unit testing of JAVA applications. Mockito is utilized to mock interfaces so that a dummy functionality can be integrated into a mock interface that can be utilized in unit testing. EclEmma : E
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Registration and Login with Spring Boot + Spring Security + Thymeleaf

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Hello everyone, I hope you all are well, today we will learn how to create user registration and login using Spring boot,  Spring security,  Thymeleaf, JPA, and H2DB . The  GitHub repository link is provided at the end of this tutorial. You can download the source code. Technologies used: Spring Boot 2.5.5  Spring Data JPA Spring Security  Thymeleaf  Maven 3+ Java 17  H2 Database User Interface User Registration Authentication Failed Authentication success Sign out Project Structure: Maven[pom.xml]: A Project Object Model or POM is the fundamental unit of work in Maven. It is an XML file that contains information about the project and configuration details utilized by Maven to build the project. It contains default values for most projects. Some of the configurations that can be designated in the POM is the project dependencies, the plugins or goals that can be executed, the build profiles, and so on. Other information such as the project version, description, developers, mailing lists
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Spring boot video streaming example-HTML5

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Hello everyone, Today we will learn how to stream MP4 video using Spring Boot and Spring Web Flux.  The Source code download link is provided at the end of this post. New, Quarkus Practice User Interface   Project Structure: G radle(build.gradle) plugins { id 'org.springframework.boot' version '2.5.4' id 'io.spring.dependency-management' version '1.0.11.RELEASE' id 'java' } group = 'com.knf.demo' version = '0.0.1-SNAPSHOT' sourceCompatibility = '11' repositories { mavenCentral() } dependencies { implementation 'org.springframework.boot:spring-boot-starter-webflux' testImplementation 'org.springframework.boot:spring-boot-starter-test' testImplementation 'io.projectreactor:reactor-test' } test { useJUnitPlatform() } Service (VideoStreamingService.java) package  com.knf.demo.service ; import org.springframework.beans.factory.annotation. Autowired ; import org.springframew
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Java Stream API - How to convert List of objects to another List of objects using Java streams?

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Hello everyone, here we will show you how to convert a List of objects to another List of objects in Java using the Java streams map(). The ‘map’ method maps each element to its corresponding result.   Java Stream API The Java Stream API provides a functional approach to processing collections of objects. The Stream in Java can be defined as a sequence of elements from a source Collection or Array. Most of the stream operations return a Stream. This helps create a chain of stream operations(stream pipe-lining). The streams also support the aggregate or terminal operations on the elements. for example, finding the minimum or maximum element or finding the average etc...Stream operations can either be executed sequentially or parallel. when performed parallelly, it is called a parallel stream. Stream map() Method The Java 8 Stream map() is an intermediate operation.It converts Stream<obj1> to Stream<obj2>. For each object of type obj1, a new object of type obj2 is created and
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Java, Spring Boot Mini Project - Library Management System - Download

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Hello everyone, Hope you are doing well. Here, we provide a Library Management System mini-project for beginners, it's free for download. Maybe you can build more on top of this project and create your own product, that's all about you. The source code download link is provided at the end of this post. 1. Benefit of this project You could cover the following technologies and features by learning and debugging this mini project. Java 17 Java Stream Java Lamda Expressions Java Records Functional programming Object-oriented programming var Keyword in Java Generics in Java Java Switch Spring boot 2.6.4 Spring Security Thymeleaf template engine OpenCSV Spring Data JPA Server Side Pagination H2 Database  Bootstrap HTML CSS and more... 2. Objective Of Spring Boot On Library Management System The main objective of this project is to manage the details of the books, author, category, and publisher. Only Admin/Librarian will manage all these activities. Also, they can export the data in
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ReactJS, Spring Boot JWT Authentication Example

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Hello everyone, In this tutorial, we’ll create a user registration & login example using ReactJS, Spring Boot, Spring Security, and JWT authentication. You could download the source code from our Github repository, the download link is provided at the end of this tutorial. Technologies used Backend Technologies: Java 17 Spring Boot 2.7.0 Spring Security Spring Data JPA JWT H2 Database Frontend Technologies: React 17.0.1 Axios 0.27.2 Redux 4.0.5 Bootstrap 4.5.2 ReactJS - SpringBoot - JWT - Flow Backend Project Directory: Frontend Project Directory: Following is the screenshot of our application - User Registration: User Signin: Profile View: Access Resource: We will build two projects:  1. Backend:   spring-boot-security-jwt 2. Frontend: react-redux-jwt Project 1: spring-boot-security-jwt Pom.xml <?xml version = "1.0" encoding = "UTF-8" ?> <project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns:xsi = "http://www.w3.org/2001/XMLSchem
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Custom Exception Handling in Quarkus REST API

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Hello everyone, In this article, we will learn how to handle exceptions in the Quarkus REST application using ExceptionMapper interface implementations. ExceptionMapper is a contract for a provider that will map a thrown application exception to a Response object. We will show you custom exception handling with the help of a simple application, Project Directory: application.properties knowledgefactory.custom.error.msg.usernotfound = User not found knowledgefactory.custom.error.msg.badrequest.numeric = User Id must be numeric Create Error Message package org.knf.dev.demo.exception; public class ErrorMessage { private String message; private Boolean status; public String getMessage() { return message; } public void setMessage( String message) { this .message = message; } public Boolean getStatus() { return status; } public void setStatus( Boolean status) { this .status = status; } public Erro
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Spring Boot + OpenCSV Export Data to CSV Example

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Hello everyone, today we will learn how to export and download the data as a CSV file in a Spring Boot project. CSV stands for Comma-Separated-Values and it's a common format for doing a bulk data transfer between systems. For creating and parsing CSV files, we will use OpenCSV 3rd-party library. A little bit of Background Spring Boot Spring Boot makes it easy to create stand-alone, production-grade Spring-based Applications that you can "just run".  More Info -  https://spring.io/projects/spring-boot OpenCSV OpenCSV is an easy-to-use CSV (comma-separated values) parser library for Java. It was developed because all the CSV parsers at the time didn’t have commercial-friendly licenses. Java 8 is currently the minimum supported version.   More Info -  http://opencsv.sourceforge.net/ Technologies used   Java 17 Spring Boot 2.7.0 OpenCSV 5.6 Spring Data JPA H2DB Maven Project directory Maven [pom.xml] A Project Object Model or POM is the fundamental unit of work in Maven. It
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Spring Webflux File Download Example

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Hello everyone, Here we will show you an example of how to download files in a Spring WebFlux application. More related topics: Spring Webflux File Upload (Single/Multiple)- REST API Example Kotlin + Spring Webflux File Upload (Single/Multiple)- REST API Example Kotlin + Spring Webflux File Download - REST API Example Reactive Rest CRUD APIs using Spring Boot, WebFlux, and Reactive Mongo Technologies Used: Spring Boot 2.5.4 Spring Webflux 2.5.4 Java 11 Maven 3 Project Structure: Project Dependency Management Spring boot dependencies, no need for the extra library for file upload. <? xml version ="1.0" encoding ="UTF-8" ?> < project xmlns ="http://maven.apache.org/POM/4.0.0" xmlns: xsi ="http://www.w3.org/2001/XMLSchema-instance" xsi :schemaLocation ="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" > < modelVersion >4.0.0</ modelVersion > < parent > &l
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