Migrating to Java 9 modules

The folder reservation-system contains a Maven project consisting of just one module. (it's similar to the one on first exercise). You'll separate this app in three different modules.

Maven modules (managed by pom.xml files) and modules descriptor (module-info.java) complement each other. But, they play different roles. Maven brings the functionality of automatic, centralized dependency management. And the module descriptors handle the modularity at Java platform level. Let's see how they work together.

Running mvn clean package generates just one jar that can be run with java -jar target/reservation-system-1.0-SNAPSHOT.jar

On the pom.xml change the Java version from 1.8 to 11.
Change the packaging from jar to pom to allow maven submodules.
Under the reservation-system folder we need to add three different folders, each of them will contain a moduel.
1. flightmodule
2. hotelmodule
3. packagemodule

For each of the modules we need to declare a pom.xml referencing the parent module. Here's what's needed for flightmodule.

<parent>
    <groupId>com.udacity.flight</groupId>
    <artifactId>reservation-system</artifactId>
    <version>1.0-SNAPSHOT</version>
</parent>
 
<artifactId>flightmodule</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<name>flightmodule</name>

Add similar pom.xmls for the other modules

Add a modules section to the parent pom.xml

<modules>
    <module>flightmodule</module>
    <module>hotelmodule</module>
    <module>packagemodule</module>
</modules>

Move the classes from parent module to each submodule (from package com.udacity.fligth to flightmodule, com.udacity.hotel to hotelmodule, and com.udacity.packagesearch to packagemodule). Each submodule should have the structure of a Maven project (with the directory src/main/java).

After doing this, the classes on packagemodule will lose some visibility on classes, so let's add the required dependencies to its pom.xml to recover that visibility.

<dependencies>
    <dependency>
        <groupId>com.udacity.flight</groupId>
        <artifactId>hotelmodule</artifactId>
        <version>1.0-SNAPSHOT</version>
        <scope>compile</scope>
    </dependency>
    <dependency>
        <groupId>com.udacity.flight</groupId>
        <artifactId>flightmodule</artifactId>
        <version>1.0-SNAPSHOT</version>
        <scope>compile</scope>
    </dependency>
</dependencies>

Move the declaration of maven-jar-plugin to packagemodule since it's the one that contains the mainClass.
Now the project is modularized at Maven level, to convert it in a Java modularized project we need to add the module-info.java, they will be in the src/main/java directory of each of them. These files are similar to what we did on exercise one.
The project should build with mvn clean package but now it will create three different jars, to run them you need specify the dependencies like this: java -cp flightmodule/target/flightmodule-1.0-SNAPSHOT.jar:hotelmodule/target/hotelmodule-1.0-SNAPSHOT.jar:packagemodule/target/packagemodule-1.0-SNAPSHOT.jar com.udacity.packagesearch.search.Main

haohao1-12/Java_Module_Exercise

Migrating to Java 9 modules