How to use ServiceLoader to load modular components in Java 9

How to use ServiceLoader to load modular components in Java 9

With the release of Java 9, modularization has become an important feature of Java application development. Modularization can effectively solve dependency management and internal access control problems in Java applications. In this article, we will introduce how to use ServiceLoader to load modular components in Java 9.

1. Introduction to modularization

Java 9 introduces a modular system that splits the application into a set of modules. Each module has its own code and resources, and can specify other module dependencies. Modules can use export and import to access other modules. This modular design makes Java applications clearer and more maintainable.

2. Introduction to ServiceLoader

ServiceLoader is a mechanism provided by Java for loading and instantiating service interface implementation classes. This mechanism allows us to dynamically load any implementation class at runtime without explicitly calling the specific implementation class in the code. This mechanism is particularly important in modular applications, since dependencies between modules can be dynamically resolved and loaded at runtime.

3. Use ServiceLoader to load modular components

First, we need to define a service interface, and use the modular syntax of Java 9 to explicitly use the interface as a service interface when defining.

module com.example.myapp.services {
    exports com.example.myapp.services;
}

Next, in the implementation class of the service interface, we need to use the ServiceLoader.Provider annotation to mark the implementation class as the implementation class of the service interface.

import com.example.myapp.services.MyService;

public class MyServiceImpl implements MyService {

    @Override
    public void doSomething() {
        System.out.println("Doing something...");
    }

}

Then, in another module, we can use ServiceLoader to load and use the implementation class of the service interface.

import com.example.myapp.services.MyService;

public class MyApp {

    public static void main(String[] args) {
        ServiceLoader<MyService> serviceLoader = ServiceLoader.load(MyService.class);
        for (MyService myService : serviceLoader) {
            myService.doSomething();
        }
    }

}

In the above code, we load the implementation class of the service interface through the ServiceLoader.load method. We can then iterate through the ServiceLoader object to obtain instances of all implementation classes and call their methods.

4. Benefits of using ServiceLoader to load modular components

Using ServiceLoader to load modular components has the following benefits:

1. Dynamic loading: Through ServiceLoader, we can The implementation class of the service interface is dynamically loaded at runtime, which makes the code more flexible and extensible.
2. Decoupling: Using ServiceLoader to load components can decouple the dependencies between components. Components can be loaded at runtime by implementing a unified service interface without explicitly specifying the component's implementation class in the code.
3. Plugability: Using ServiceLoader, we can easily add new components to the application, even without downtime. This makes the application more scalable and maintainable.

5. Summary

This article briefly introduces the use of ServiceLoader to load modular components in Java 9. Through ServiceLoader, we can dynamically load the implementation class of the service interface, achieving dependency decoupling and pluggability between components. This feature makes Java 9 a more flexible and extensible development platform.

Reference:

1. Java 9 Modular System (https://openjdk.java.net/projects/jigsaw/)
2. ServiceLoader in Java 9 (https://docs.oracle.com/javase/9/docs/api/java/util/ServiceLoader.html)

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