modular programming in java 9 pdf

In general, the option to add the named modules to the default set of root modules is –add-modules (,)* where is a module name. Rethinking Java development with packages. The canonical reference for building a production grade API with Spring. Having this information explicitly encoded into modules (with the dependencies) makes it much easier to create reliable applications, especially if you apply these same principles to your application development. An important organizational aspect of Java 9 is dividing the JDK into modules to support various configurations as is outlined in JEP 200. Focus on the new OAuth2 stack in Spring Security 5. Next, we have the with directive where we provide the implementation class name that either implements the interface or extends the abstract class. This file is known as the module descriptor and contains all of the data needed to build and use our new module. Wait, you say. This textbook is one of many collections And also introduces one other new component: the module descriptor module-info.java. By Mohamed Taman Published November 7, 2019. Java 9, a new kind of programming component called module has been introduced. 0000012298 00000 n For those who need a refresher, a Java SE 8 application: In Java 8 and earlier applications, the top-level component is the package. 0000013128 00000 n Let's see what this looks like: A service is an implementation of a specific interface or abstract class that can be consumed by other classes. The goal was to decrease the application startup time. The module has a unique name. A module is a collection of code, data, and resources. Now, create a new class file called MainApp.java. Here is where we put the interface or abstract class name. We'll be using the command line for our full example down below to help solidify how the entire system works in our minds. 0000008634 00000 n As of now, Java 9 Module System has 95 modules in Early Access JDK. We designate the services our module consumes with the uses directive. 0000007065 00000 n Create a file called compile-simple-modules.sh: There are two parts to this command, the javac and find commands. Any packages defined in a module and not exported are privately encapsulated and can never be accessed. For example, when we try to run Java 8 programs as-is with Java 9 compiler we may need to add modules. The main goal of the Java 9 module system is to support modular programming in Java. If all works, you should see: Now that we have a basic understanding of how to build a module, let's make it a little more complicated. A module descriptor is a Java file. Add the following to our module-info.java: As we can see, we declare the interface and which class implements it. 0000003297 00000 n A module can also be a service provider that other modules can consume. A lot of libraries depend on reflection to work their magic (JUnit and Spring come to mind). In a Java 9 module, the module descriptor is a resource that contains module metadata that describes the module. For example, when we try to run Java 8 programs as-is with Java 9 compiler we may need to add modules. Nothing was truly encapsulated, which can open up all kinds of problems for developers of the libraries. 0000002192 00000 n We will keep the code simple: And finally, in the hello.modules root directory, add in our module descriptor; module-info.java: To keep this example simple, all we are doing is exporting all public members of the com.baeldung.modules.hello package. Contents ; Bookmarks Introducing Java 9 Modularity. We need to list all packages we want to be public because by default all packages are module private. By the way, each Java 9 module can be only one module with one module descriptor. This is because it contains such foundational classes as Java objects, Integer, String, and so on. Next, we talked about how to discover which modules are included in the JDK. We can create multi-module projects comprised of a “main application” and several library modules. As you can see in the image, java.base is the module that every other module depends on. The default module for all JDK and user-defined modules is the base module java.base. We could put the implementation into a private package while exposing the interface in a public package.

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