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A Guide to Crawler4j 1. Introduction We see web crawlers in use every time we use our favorite search engine. They’re also commonly used to scrape and analyze data from websites. In this tutorial, we’re going to learn how to use crawler4j to set up and run our own web… Continue Reading crawler4j
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Throw Exception in Optional in Java 8 1. Introduction In this tutorial, we’re going to show how to throw a custom exception when an Optional is empty. If you want to go deeper into Optional, take a look at our full guide, here. 2. Optional.orElseThrow Simply put, if the value is present, then isPresent() would return… Continue Reading java-optional-throw-exception
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Guide to Java Instrumentation 1. Introduction In this tutorial, we’re going to talk about Java Instrumentation API. It provides the ability to add byte-code to existing compiled Java classes. We’ll also talk about java agents and how we use them to instrument our code. 2. Setup Throughout the article, we’ll build an… Continue Reading java-instrumentation
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Jersey Filters and Interceptors 1. Introduction In this article, we’re going to explain how filters and interceptors work in the Jersey framework, as well as the main differences between these. We’ll use Jersey 2 here, and we’ll test our application using a Tomcat 9 server. 2. Application Setup Let’s first… Continue Reading jersey-filters-interceptors
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Finding Min/Max in an Array with Java 1. Introduction In this short tutorial, we’re going to see how to find the maximum and the minimum values in an array, using Java 8’s Stream API. We’ll start by finding the minimum in an array of integers, and then we’ll find the… Continue Reading java-array-min-max
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Visibility Modifiers in Kotlin 1. Introduction The Kotlin programming language is built upon the Java Virtual Machine (JVM). As such, it has to follow all of the rules that the JVM imposes – including visibility modifiers. However, there are some subtle nuances in how the language implements these modifiers with… Continue Reading kotlin-visibility-modifiers
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Calculate the Area of a Circle in Java 1. Overview In this quick tutorial, we’ll illustrate how to calculate the area of a circle in Java. We’ll be using the well-known math formula: r^2 * PI. 2. A Circle Area Calculation Method Let’s first create a method that will perform the… Continue Reading java-calculate-circle-area
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Java Weekly, Issue 266 Here we go… 1. Spring and Java ===== >> Testing CDI Beans and the Persistence Layer Under Java SE [in.relation.to] A good write-up on using Weld to test interactions between the JPA layer and the business logic layer without incurring the overhead of container deployments. >> Adding Input… Continue Reading java-weekly-266
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Spring Security Authentication Provider 1. Overview This tutorial will show how to set up an Authentication Provider in Spring Security to allow for additional flexibility compared to the standard scenario using a simple UserDetailsService. 2. The Authentication Provider Spring Security provides a variety of options for performing authentication. These follow… Continue Reading spring-security-authentication-provider
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Hibernate Inheritance Mapping 1. Overview Relational databases don’t have a straightforward way to map class hierarchies onto database tables. To address this, the JPA specification provides several strategies: MappedSuperclass – the parent classes, can’t be entities Single Table – the entities from different classes with a common ancestor are placed… Continue Reading hibernate-inheritance
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