https://github.com/temikfart/java-classloading
Here are examples of loading classes and modules using custom class loaders in Java 8 and Java 9+.
https://github.com/temikfart/java-classloading
classloaders classpath guide habr java-8 java-9 java-9-modules module-api module-path module-system
Last synced: 3 months ago
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Here are examples of loading classes and modules using custom class loaders in Java 8 and Java 9+.
- Host: GitHub
- URL: https://github.com/temikfart/java-classloading
- Owner: temikfart
- License: mit
- Created: 2023-11-21T13:21:53.000Z (over 1 year ago)
- Default Branch: main
- Last Pushed: 2024-01-24T14:02:45.000Z (over 1 year ago)
- Last Synced: 2025-01-13T04:29:03.826Z (5 months ago)
- Topics: classloaders, classpath, guide, habr, java-8, java-9, java-9-modules, module-api, module-path, module-system
- Language: Java
- Homepage:
- Size: 1.46 MB
- Stars: 3
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
## Java Class Loading examples
---
This repository contains the code for all the examples from [the article on Habr](https://habr.com/ru/companies/isp_ras/articles/788618/).
Each example comes with its own README.md.
Each example demonstrates how class loaders are associated with `classpath`/`modulepath`. Examples using Java versions 8 and 17 are considered, where the main difference is the modular system that appeared in Java 9.
Examples:
- Java 8
- [Manual Loading](java-8/manual)
- [Auto Loading](java-8/auto)
- Java 17
- Manual
- One Module
- [Java 8 Style](java-17/manual/one-module/java8style)
- [Java 17 Style](java-17/manual/one-module/java17style)
- Few Modules
- [Together](java-17/manual/few-modules/together)
- Separately
- [No Dependencies](java-17/manual/few-modules/separately/no-deps)
- [No Dependencies (hack)](java-17/manual/few-modules/separately/no-deps-hack)
- [With Dependencies](java-17/manual/few-modules/separately/with-deps)
- Auto
- One Module
- [Java 8 Style](java-17/auto/one-module/java8style)
- [Java 17 Style](java-17/auto/one-module/java17style)
- Few Modules
- [Together](java-17/auto/few-modules/together)
### Used classes
---
Each example uses just a few classes for demonstration purposes. Below are the features of each of them.
#### class `Main`
---
A class with a `main` method, in which, depending on the example, either the simplest classes `Cat` or `Dog` are loaded, or instances of the simplest classes are created. At the end of the method, the `talk` method is called on an instance of the simplest class.
Between instantiation and calling the `talk` method, information about class loaders and/or the name of the modules to which the classes belong is printed.
#### class `CustomClassLoader`
---
A custom class loader that almost completely satisfies the [**delegation model**](https://docs.oracle.com/javase/tutorial/ext/basics/load.html), except that it first tries to load the class , and only then delegate to the parent loader.
Methods:
- `loadClass`:
1. First, an attempt is made to find a class among the loaded classes;
2. Then an attempt is made to load the class yourself, if it is from the application;
3. If the class is not from the application, then the loading is delegated to the ancestor.
- `findClass`: Loads the bytecode of a class (if found) and defines it as a class.
If you try to load a class from the `java.*` package, the JVM will throw `java.lang.SecurityException: Prohibited package name: java.*`. To determine that the class is from an application, it checks that [binary name](https://docs.oracle.com/javase/specs/jls/se17/html/jls-13.html#jls-13.1) begins with `ru.ispras`.
#### class `Cat`
---
The simplest class to load with a single `talk` method that prints the word *"Meow"* to `stdout`.
#### class `Dog`
---
The simplest class to load with a single `talk` method that prints the word *"Woof"* to `stdout`.