together

Java 17. Manual Loading (dependent and dependency)

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Task: load any application class using a custom class loader (CustomClassLoader) from another module (the modules are linked via module-info.java).

Solution

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Modules (declared via module-info.java):

• manual.fewmodules.together.dependent:
  • Main - a class containing the main method, where an instance of the CustomClassLoader class is created, the Cat class is loaded using it, creating an instance of the class Cat and calling the Cat::talk method;
  • CustomClassLoader - a class that is an implementation of a custom class loader;
• manual.fewmodules.together.dependency:
  • Cat - loadable class with the talk method, which prints the string "Meow" to stdout.

Run

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Using modulepath:

java17 -p dependent-1.0.jar:dependency-1.0.jar -m manual.fewmodules.together.dependent

Output:

Main Class Module is module manual.fewmodules.together.dependent
Cat Class Module is unnamed module @23fc625e
Main Class ClassLoader is jdk.internal.loader.ClassLoaders$AppClassLoader@42a57993
Cat Class ClassLoader is ru.ispras.j17.manual.fewmodules.together.dependent.CustomClassLoader@3fee733d
Meow

Explanation

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Same as in Java 17. Manual Loading (Java 17 style).

Notes

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Same as in Java 17. Manual Loading (Java 17 style).

• In module-info.java of the dependency module you need to export the package with the Cat class, and in module-info.java of the dependent module you need to specify the dependency on the dependency module:

// dependency/src/module-info.java
module manual.fewmodules.together.depedency {
    exports ru.ispras.j17.manual.fewmodules.together.dependency;
}

// dependent/src/module-info.java
module manual.fewmodules.together.dependent {
    requires manual.fewmodules.together.dependency;
}