How to use the module system in Java 9 to separate and isolate code

How to use the module system in Java 9 to separate and isolate code

As the size of software continues to expand, the complexity of the code continues to increase. To better organize and manage code, Java 9 introduced the module system. The emergence of the module system solves the problem of traditional package dependencies, making the separation and isolation of code easier and more flexible. This article will introduce how to use the module system in Java 9 to achieve separation and isolation of code.

1. Definition of module

In Java 9, we can use the module keyword to define a module. A module consists of a set of packages, and the access rights of the packages in the module are controlled through the exports keyword. A module can depend on other modules, and the dependencies between modules are represented by the requires keyword.

The following is an example of a simple module definition:

module com.example.myapp {
    requires java.base;
    requires com.example.mylib;
    exports com.example.myapp;
}

In this example, com.example.myapp is a module that depends on the java.base module and the com.example.mylib module . It exposes the com.example.myapp package to the outside world through the exports keyword, and other modules can access the package.

2. The use of modules

When developing Java applications, we can organize the code into different modules, each module is responsible for different functions. The advantage of this is that it can better manage the code, reduce coupling, and improve the maintainability and reusability of the code.

We use a simple example to illustrate how to use the module system to separate and isolate code. Suppose we have a project called myapp, which consists of two modules: myapp and mylib.

First, we create a mylib module, which contains a Helper class:

module mylib {
    exports com.example.mylib;
}

Then, we create a myapp module, which depends on the mylib module and uses the Helper class in the mylib module :

module myapp {
    requires mylib;
    exports com.example.myapp;
}

In the myapp module, we can use the import keyword to introduce classes in the mylib module:

import com.example.mylib.Helper;

public class MyApp {
    public static void main(String[] args) {
        Helper helper = new Helper();
        helper.doSomething();
    }
}

By using the module system, we can clearly separate and isolate different code modules . During compilation and runtime, the Java virtual machine automatically resolves dependencies between modules and loads the required modules.

3. Module packaging and publishing

In Java 9, we can use the jlink command to create a self-contained runtime image. The runtime image contains all modules and dependencies required by the application and can be run directly in the target environment.

Suppose we have packaged myapp and mylib modules into jar files. We can use the following command to create a runtime image:

jlink --module-path modules --add-modules myapp --output image

Among them, the --module-path parameter specifies the directory where the module is located, the --add-modules parameter specifies the module to be packaged, and the --output parameter specifies the output. Table of contents.

After the creation is completed, we can directly run the self-contained runtime image:

./image/bin/java -m com.example.myapp/com.example.myapp.MyApp

By using the jlink command, we can easily package and publish a self-contained application, reducing the need for The need for external dependencies improves application portability.

Summary:

The module system in Java 9 provides us with better code organization and management solutions. By defining modules and using dependencies between modules, we can achieve separation and isolation of code. The emergence of the module system makes code maintenance more convenient, reduces coupling, and improves code reusability and maintainability. At the same time, by using the jlink command, we can create self-contained runtime images to package and publish applications, reducing the need for external dependencies and improving portability. Therefore, when developing Java applications, we should make full use of the module system in Java 9 to optimize code structure and modular development.

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