Java Modulus / Modulo operator – Examples and Uses

Java Modulus / Modulo operator – Examples and Uses

The Java modulus ‘%’ operator is one of numerous operators built into the Java programming language. The operator is used to calculate the remainder of the division between two numbers. First, let us discuss how the operator works.   How to use the ‘%’ operator:   The ‘%’ operator requires two operands. The first is […]

JPA / Hibernate – Mapping One-to-One relationships

JPA / Hibernate – Mapping One-to-One relationships

  In this tutorial, we will discuss how to map and configure One-to-One relationships in JPA and Hibernate.   What are One-To-One relationships? One to One relationships in databases define the relationship between two different entities, where the first entity can be related to zero or one of the second entity. For example, a user […]

How to manage JPA bidirectional relationships properly

How to manage JPA bidirectional relationships properly

In this troubleshooting guide, we will explore how to properly map bidirectional relationships and common mapping pitfalls that cause exceptions such as DataIntegrityViolationException, a ConstrainViolationException and a PropertyValueException. We will take an unusual approach in this guide by first building the faulty software, and then we will discuss how and why this should be fixed. […]

Configuring and mapping database tables to JPA entities

Configuring and mapping database tables to JPA entities

  In this post, we will explore how to map a database tables to JPA Entities. In our example, we will use a Spring Boot environment, JPA 2.2 and Hibernate 5.3.7 . However, the information presented here should apply to any environment with a JPA version of 2.1 or later.   Introduction   In our […]

org.hibernate.MappingException: Could not determine type for: java.util.List – Causes & Fixes

org.hibernate.MappingException: Could not determine type for: java.util.List – Causes & Fixes

The error In this post, we will explore a very common Hibernate error, namely a MappingException caused by missing annotations on the Entity getters and fields. Let us check the following stack trace as an example:  

  In the next section, we will display the faulty implementation that caused the error above. If you […]

Getting started with Spring boot 2 and JPA

Getting started with Spring boot 2 and JPA

  In this tutorial, we will build a simple Spring boot 2 application with access to a Postgres database using JPA.   Background:   Before we get started, let us get a couple of definitions out of the way.   What is JPA? JPA stands for the “Java Persistence API”. It is a java specification […]

Create, configure and test an MBean in Spring boot using Java config and Jolokia

Create, configure and test an MBean in Spring boot using Java config and Jolokia

Summary: In this article, we will create a new custom MBean. We will show how to configure this bean and then we will test it using Jolokia (JMX over HTTP).   Prerequisites: If you have not yet configured Jolokia, then we suggest that you go over this article https://nullbeans.com/how-to-configure-jolokia-on-a-spring-boot-server/ before you proceed.   Introduction: Managed beans (MBeans) […]

How to configure Jolokia on a Spring boot server

How to configure Jolokia on a Spring boot server

Summary:   In this article, we will find out how to configure Jolokia on a Spring Boot 2 server. We will also configure Jolokia on a different management port and a different base URL.   Background:   Jolokia is a JMX over HTTP bridge that allows system administrators to access their MBeans and JMX functionalities […]

The Java Comparable interface – Automatically sort collections

The Java Comparable interface – Automatically sort collections

Summary: In this post, we will explore how to use the Java comparable interface to automatically sort collections of any classes. We will use the Java Collections from the util library as an example.   Introduction: Java interfaces are one of the most powerful features of the object oriented programming language. When a class implements […]

How to squeeze more performance out of ArrayLists

How to squeeze more performance out of ArrayLists

In this post we will discuss how to improve the performance of Java programs that utilize ArrayLists by setting the list’s initial capacity.   ArrayLists and lists in general are great data structures for storing data. They are convenient for when we don’t know how large our data set. However, this comes with a performance […]