Load dynamic library java that inherit interface

Question

I want to load dynamic library where classes inherit from an interface/abstract class on my core project, so I can load my classes at runtime and use it. How can i do that ?

Example:

Core: ITrigger (interface)

Library: {MyTriggerOne extends ITrigger} {MyTriggerTwo extends ITrigger}

score 0 · Answer 1 · answered Dec 08 '16 at 09:41

0

If you want to load a class/library dynamically use Class.forName('class name') method to load.

answered Dec 08 '16 at 09:41

Upesh M

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Yes, but the class name are not the same, so how could i load classes dynamically without the classname known – liege30 Dec 08 '16 at 09:47
Without knowing the classname it will be difficult. One solution is to load the entire library/jar using Class.forName and then using reflection identify the class which implements your interface, then create an instance of that class. – Upesh M Dec 08 '16 at 09:55
If i load the entire jar using Class.forName, my jar become a "class" and my classes inside the jar becomer "inner classes" ? – liege30 Dec 08 '16 at 10:00
use this solution to load your class from jar http://stackoverflow.com/questions/11016092/how-to-load-classes-at-runtime-from-a-folder-or-jar – Upesh M Dec 08 '16 at 10:40

mohan rathour · Answer 2 · 2016-12-08T10:44:45.557

0

Java's SPI(Service Provider Interface) libraries allow you to load classes dynamically based on the interfaces they implement, that can be done with the help of META-INF/services.

You can create a interface like

package com.test.dynamic;
public interface ITrigger {
    String getData();
    String setData();
}

you can use the ServiceLoader class to load the interface like below code

ServiceLoader<ITrigger> loader = ServiceLoader.load(ITrigger.class);

then you can perform all the operation on it. If you have some other implementing classes on your classpath, they register themselves in META-INF/services. you need to create a file in META-INF/services in your classpath with the following properties

The name of the file is the fully qualified class name of the interface, in this case, it's com.test.dynamic.ITrigger
The file contains a newline-separated list of implementations, so for the example implementation, it would contain one line: com.test.dynamic.impl.SomeITriggerImplementation class.

edited Dec 08 '16 at 10:44

answered Dec 08 '16 at 09:48

mohan rathour

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I must register the implementing classes in the main JAR program or on the library JAR ? – liege30 Dec 08 '16 at 10:06
you need to create a file in META-INF/services in your classpath with some property like – mohan rathour Dec 08 '16 at 10:22
I must create my META-INF here ? -> src/main/resources/META_INF/ – liege30 Dec 08 '16 at 10:29
ya or you can use some build tolls like Maven, Ant, etc – mohan rathour Dec 08 '16 at 10:45

score 0 · Answer 3 · answered Dec 08 '16 at 10:31

I had the same requirement and I used the library Reflections.

Very simple code snippet:

public Set<Class<? extends ITrigger>> getITriggerClasses() {
    final Reflections reflections = new Reflections("package.where.to.find.implementations");
    return reflections.getSubTypesOf(ITrigger.class);
}

Then you can use the method Class::newInstance to create the ITrigger(s). This is a very simple example, there are several options to initialize the Reflections class (not only with one package name).

Load dynamic library java that inherit interface

3 Answers3