How to implement modularization and Jigsaw of Java underlying technology

For Java developers, modularization is a very important technology. It can help us better organize code, reduce coupling, and improve code maintainability and readability. Java 9 introduces the Jigsaw module system, which provides a new modular approach that makes it easier for developers to create, manage, and use modular code. This article will introduce how to implement modularization and Jigsaw of Java's underlying technology, and provide specific code examples.

1. What is modularity?

Modularization refers to dividing the entire application into a series of modules (or components). Each module has its own functions and responsibilities, and they are independent of each other. In Java, a module can contain classes, interfaces and other resource files, and can also specify externally provided APIs and other dependent modules.

2. Introduction to Jigsaw

Jigsaw is a major feature introduced in Java 9. It provides a new modular approach that makes it easier for developers to create, manage and use Modular code. Jigsaw mainly includes the following functions:

1. Define module: Developers can define a module through the module-info.java file, which contains the module's name, API, dependencies and other information.
2. Module path: Modules can reference other modules in a more intuitive way, without the need to reference them through the class path.
3. Restrict access: Modules can restrict the access rights of other modules through export and exposure to improve code security.
4. jlink tool: You can use the jlink tool to package a runtime image that contains only the application modules and their dependencies.

3. Implementing modularization and Jigsaw

Below we use a specific example to demonstrate how to use Jigsaw to implement modular Java applications. We will create a simple application that contains two modules: a Hello module for printing Hello World, and a Greeting module for providing services for printing Hello World.

1. Create module

First, we need to create a module called Hello, which will depend on the Greeting module. Create the following structure in the root directory of the project:

hello-module
|--src
   |--hello
      |--module-info.java
      |--com
         |--example
            |--hello
               |--Hello.java
|--greeting-module
   |--src
      |--greeting
         |--module-info.java
         |--com
            |--example
               |--greeting
                  |--GreetingService.java

2. Define module information

Define module information in module-info.java of Hello module and Greeting module respectively:

Hello module module-info.java:

module hello {
    requires greeting;
}

Greeting module module-info.java:

module greeting {
    exports com.example.greeting;
}

3. Implementation code

Next, let’s implement the code of the Hello module and the Greeting module.

Hello.java of Hello module:

package com.example.hello;

import com.example.greeting.GreetingService;

public class Hello {
    public static void main(String[] args) {
        GreetingService greetingService = new GreetingService();
        System.out.println(greetingService.getGreeting());
    }
}

GreetingService.java of Greeting module:

package com.example.greeting;

public class GreetingService {
    public String getGreeting() {
        return "Hello, World!";
    }
}

4. Compilation and operation

Complete After writing the code, we can use the javac command to compile the Hello module and the Greeting module respectively:

javac -d out/hello --module-source-path hello-module/src hello-module/src/hello/module-info.java hello-module/src/com/example/hello/Hello.java

javac -d out/greeting --module-source-path greeting-module/src greeting-module/src/greeting/module-info.java greeting-module/src/com/example/greeting/GreetingService.java

Then, we can use the java command to run the Hello module:

java --module-path out/hello --module hello/com.example.hello.Hello

Summary

Through the above examples, we can see that the Jigsaw modular system provides us with a more structured and standardized way to organize and manage code. It can help us reduce the coupling between modules and improve the maintainability and readability of the code. By carefully studying Jigsaw, we can better leverage it to build more robust, maintainable, and scalable Java applications. I hope this article will be helpful for everyone to understand and use the modularization and Jigsaw of Java's underlying technology.

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