Java 9 Modularity: First Look

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The module system usually loads all the modules from the module path, but also all the jar files in the classpath, if present. First, you'll learn what modules are and how modular design using the Java module system increases the flexibility, maintainability, and security of your applications. This feature is intended to improve startup time of both small and large applications, with limited impact on peak performance.

This article uses simple names to avoid lengthy commands, making them easier to grasp. When this file is compiled, Java creates a file called module-info. Java 9, a new kind of programming component called module has been introduced.

Java 9, OSGi and the Future of Modularity (Part 1)

Since then, we've slowly started to do some discussions in this expert group. The module system consists of a dependency- and a service model. The dependency model is based on exported packages and required modules. It introduces a new namespace for modules so that it can require them. A module can limit the exports to friend modules and a module can re-export its dependencies. It is basically a Require-Bundle with re-exports but without any versions. This file is not extensible and does not support annotations. I just wish the dependency model was symmetric. That is, require should use package names instead of module names. Around 2004 when we worked with Eclipse and they insisted on a similar model. Over time we learned that a symmetric model prevents a lot of problems. For example, if you split a bundle into two bundles then the bundles that depended on the original model do not have to be changed, they will get the imported packages from the right bundle. The proposal introduces a brand new namespace for modules but making the model symmetric would make this complexity unnecessary. The most surprising part for me java 9 module system the proposal was the lack of versions. This seems to imply that the build system will generate the module-info. When we make module-path an artifact created by the build system we can probably make the module system even simpler, I think. It will be interesting to see how the industry reacts to this strong encapsulation. A module can 'use' a service by its interface name and 'provide' a service by specifying the interface and implementation class tuple. Service Loader services are like global variables and are created only on request without context. For example, in the we have a railway track with multiple trains. In the the train bundles run local and are represented by a Train Manager service. The number of instances depends on the bundles and the configuration of those bundles. In the real world the trains run on a Raspberry Pi. The static Service Loader model can of course not help in these scenarios. My concerns are that there are some implications in the current design that would make it possible to reduce the complexity of the module dependency model even further by reifying the module path. For the service model I find the Service Loader too simple. The trend to microservices makes it clear that modern applications must be able to transparently interact with local services as well remote java 9 module system and this cannot be modeled with Service Loader.

It only sends a new demand after collecting all the unfulfilled items. A modular application allows a team to more-safely approach large projects and produce cleaner code with superior run-time stability. Thus, nothing was truly encapsulated. Unfortunately, this situation leaves the chore of creating a modular environment up to proprietary framework conventions and configurations. Stopping at a frame that matches a given criteria avoids the cost of examining all the frames if the caller is interested only in the top frames on the stack. The introduction of Java 9 helped standardize the paradigm, which may speed up its adoption. Output It will print the following output on console. Before Java 9, reflection could be used to learn about all types in a package and all members of a type—even its private members—whether you wanted to allow this capability or not.