Understanding Custom Classloaders in Java: Practical Use Cases and Examples

source: educba.com/

Introduction

When you run a Java program, you might not think about how your code gets loaded and run. But behind the scenes, Java’s classloaders are working hard to find and load your classes. The standard classloaders handle most basic needs, but sometimes you need more control. That’s where custom classloaders come in.

In this article, we’ll explore what classloaders are, how to create your own custom classloaders, and real-world cases where they solve common problems. We’ll keep things simple and include plenty of examples to make these concepts easy to understand.

What Are Classloaders?

At its core, a classloader is just what it sounds like — a part of the Java system that loads classes into memory. When your Java program needs to use a class, a classloader finds the class file (usually a .class file) and brings it into the Java Virtual Machine (JVM).

The Default Classloader System

Java uses three main classloaders by default:

1. Bootstrap Classloader: Loads core Java classes like those in the java.lang package.
2. Extension Classloader: Loads classes from extension directories.