A good way to answer the following Spring WebFlux interview questions is to be familiar with the platform itself. This reactive-stack web framework uses a small thread pool to prevent blocking and IOC inversion of control to provide asynchronous input and output message flows. The picture below depicts how the framework works. The questions are meant to challenge your knowledge of this technology. If you have no experience, you can also refer to the tutorials provided by the Spring WebFlux team.
Spring WebFlux is a reactive-stack web framework
If you’re looking for a new web framework, you might want to consider Spring WebFlux. This reactive-stack web framework supports the Reactive Stream API, a standardized method for processing asynchronous streams. Reactive-stack applications support non-blocking backpressure, which makes them well suited for streaming scenarios. The main difference between WebFlux and Spring MVC is that WebFlux supports a different concurrent programming model than Spring MVC.
Spring WebFlux supports a lambda-based functional programming model and is compatible with many reactive libraries. Annotation programming allows application developers to create flexible controller method signatures with a variety of return values and method arguments. Additionally, it supports multiple reactive libraries, including Reactor and RxJava. By allowing applications to plug in reactive libraries, Spring WebFlux can easily adapt to the way they’re used.
It provides asynchronous input and output message flows
Spring WebFlux provides asynchronous input and output message flow, and is relatively easy to use. It includes a passive HTTP request class, the WebClient, which provides a fluent API and reactive types. Unlike Spring MVC, which assumes threads will be blocked, WebFlux assumes that they never need to pass work off. Instead, WebFlux threads behave as event loop workers, cycling through incoming requests much more quickly than their counterparts in MVC.
Spring WebFlux supports both non-blocking and asynchronous push and pull modes, and it adopts the Java lambda method for writing code that is close to the natural language. The library works in both traditional Servlet and NIO containers, and it can adapt to different HTTP service containers. It also functions as a total controller for processing requests, with multiple configurable components handling the actual work.
It uses a small thread pool to avoid blocking
Spring WebFlux is a Java application framework that can easily adapt to a variety of server APIs, including the Servlet 3.1 API. Its small thread pool and HttpHandler API provide an abstraction over various server implementations, including Reactor Netty. Depending on the server implementation, worker threads are spawned by Netty, Reactor, and Undertow. These threads are typically not larger than the number of CPU cores that are available for processing requests. The thread pool is small enough to provide good performance in reactive scenarios, as it does not need to handle housekeeping threads.
WebFlux runs on Jetty or Tomcat containers, which can be configured to use either Servlet 3.1+ or non-Servlet runtimes. It defaults to Netty, which is an excellent choice for non-blocking designs. The implementation is easy to integrate with existing infrastructure, and WebFlux is based on a different concurrent programming model than Spring MVC.
It uses IOC inversion of control
To demonstrate IOC, consider a situation where a program needs to be configured by an external application. For example, if a client wants to upload files to a server, they need to use a multipart resolver to upload them to the container. In this scenario, a single request would only be allowed if the container did not have any pending requests. In this case, the program needs to use IOC inversion of control (IOC). During the execution, the join points are performed. In the picture below, you will see an example.
Inversion of control is the principle that allows programmers to isolate code from presentation in a view. IOC containers, such as BeanFactory, are used for this purpose. BeanFactory is a container that collects definitions and beans and instantiates them when required. A layer of abstraction, called ApplicationContext, is then placed on top of the bean factory. IOC also promotes a principle of least-intrusive coupling and a least-interfering mechanism. The JDBCTemplate helps to do this by converting regular SQL exceptions into run-time ones.
It uses LiveReload in Spring MVC
You may not have heard about LiveReload yet. The underlying technology behind it is called Spring Boot Developer Tools, which auto-reloads the application whenever it changes. LiveReload is not a standalone server, but it can be used in conjunction with Spring MVC to automatically refresh the browser on any changes made to the application. It is a technology that is still in development, so you may not be able to fully take advantage of it yet.
The Grails community has long used automatic class reloading to solve this issue. You simply need to save your Java application, and it automatically loads it in the Tomcat container. This feature has been missing from Spring MVC for quite some time. To get around this issue, you can use jRebel, a third-party tool that costs $475 annually. However, if you are not building an enterprise-class application, this option may not be affordable.
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