Modern web applications and the rise of mobile clients redefined what is expected from a web server. Node.js was the first technology that recognized the paradigm shift and offered a solution.
The application platform Vert.x takes some of the innovations from Node.js and makes them available on the JVM, combining fresh ideas with one of the most sophisticated and fastest runtime environments available. Vert.x comes with a set of exciting features that make it interesting for anybody developing web applications.
Non-blocking, event driven runtime
Vert.x provides a non-blocking, event-driven runtime. If a server has to do a task that requires waiting for a response (e.g. requesting data from a database) there are two possibilities how this can be implemented: blocking and non-blocking.
The traditional approach is a synchronous or blocking call. The program flow pauses and waits for the answer to return. To be able to handle more than one request in parallel, the server would execute each request in a different thread. The advantage is a relatively simple programming model, but the downside is a significant amount of overhead if the number of threads becomes large.
The second solution is a non-blocking call. Instead of waiting for the answer, the caller continues execution, but provides a callback that will be executed once data arrives. This approach requires a (slightly) more complex programming model, but has a lot less overhead. In general a non-blocking approach results in much better performance when a large number of requests need to be served in parallel.
Simple to use concurrency and scalability
Vert.x applications are written using an Actor-like concurrency model. An application consists of several components, the so-called Verticles, which run independently. A Verticle runs single-threaded and communicates with other Verticles by exchanging messages on the global event-bus.
Because they do not share state, Verticles can run in parallel. The result is an easy to use approach for writing multi-threaded applications. You can create several Verticles which are responsible for the same task and the runtime will distribute the workload among them, which means you can take full advantage of all CPU cores without much effort.
Verticles can also be distributed between several machines. This will be transparent to the application code. The Verticles use the same mechanisms to communicate as if they would run on the same machine. This makes it extremely easy to scale your application.
Polyglot
Unlike many other application platforms, Vert.x is polyglot. Applications can be written in several languages. It is even possible to use different languages in the same application. At this point Java, Python, Groovy, Ruby, and JavaScript can be used and support for Scala and Clojure is on the way.
Conclusion
Vert.x is a relatively young platform and subsequently the ecosystem is not as rich as that of the more established platforms. Nevertheless for the most common tasks, there are extensions available. The advantages of Vert.x are astonishing. Its non-blocking, event-driven nature is extremely well-suited for modern web applications. Vert.x makes it easy to write concurrent applications that scale effortless from a single low-end machine to a cluster with several high-end servers. Add the fact that you can use most popular languages for the JVM and you have a web developers dream come true!
