@context in quarkus

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• 📋Contexts and Dependency Injection
• 📋Duplicated context, context locals, asynchronous processing and propagation
• 📋Overview of Bean Scopes in Quarkus

In this guide we’re going to describe the basic principles of the Quarkus programming model that is based on the Jakarta Contexts and Dependency Injection specification. The CDI . The CDI reference guide describes the bean discovery, non-standard features and configuration properties. The CDI integration guide has more detail on common CDI-related integration use cases, and example code for solutions. Well, a bean is a container-managed object that supports a set of basic services, such as injection of dependencies, lifecycle callbacks and interceptors. Instead, you can affect the lifecycle through declarative means, such as annotations, configuration, etc. The container is the environment where your application runs. It creates and destroys the instances of beans, associates the instances with a designated context, and injects them into other beans. An application developer can focus on the business logic rather than finding out "where and how" to obtain a fully initialized component with all of its dependencies. In CDI the process of matching a bean to an injection point is type-safe. Each bean declares a set of bean types. In our example above, the Translator bean has two bean types: Translator and java.

Duplicated context, context locals, asynchronous processing and propagation

Quarkus integrates JAX-RS so you can access the ServletContext instance by using JAX-RS @Context. // t. @Context. ServletContext servletContext; // OR. . In this article, we are going to see how to intercept requests and responses using filters in Quarkus. We will analyze how to implement them in traditional stack and in a reactive one. In this example, we'll create two rest endpoints, one using the traditional resteasy dependency and another one using web-vertex, in both cases we will build filers to be able to act on requests and responses. In particular, we are going to add headers to the response. In this section, we will look at the annotations and interfaces that will be used later in the code to achieve our goal. For the servelt container the interface ContainerResponseFilter is used to intercept the response and act on them before reaching the client. In case we want to deal with the request, we can implement the ContainerRequestFilter. For the reactive context, we will use RouteFilter annotation, which will be placed on a void method with a parameter of type RoutingContext. The method will contain the logic which will be applied to a certain route. It's a simple endpoint which returns a string, if you need to return a json you will have to add a json library to your pom.

Overview of Bean Scopes in Quarkus

From the routing context you can get the HttpServerRequest by using the t() function. Good thing about this is that you can inject this into the . In contrast to a classically POJO class instance, the instance of a bean is encapsulated and lives inside a container object. Therefore beans are called container-managed. The container takes care of the lifecycle from the dependency resolution, the instantiation to the destruction of the bean. This container is called client-proxy. A scope defines the behavior of a client-proxy. For example, this scope determines the exact times when the lifecycle of a bean starts and ends and when to reuse a bean instance or create a new one. Before we get into the scopes, we should first understand some of the essential terminologies for understanding the concepts around beans. It all starts with the understanding of dependency injection DI : A class that has a dependency on another class does not create an instance of that class itself. It just defines a dependency on the type of the class. The instance of the dependent class gets passed to the class at runtime from the outside.

Introduction to Contexts and Dependency Injection (CDI)

Vert.x duplicated context is a construct that provides the same kind of propagation but for asynchronous processing. It can also be used with synchronous code. This document explains . Traditional blocking code uses ThreadLocal variables to store contextual objects in order to avoid passing them as parameters everywhere. Many Quarkus extensions require those contextual objects to operate properly: Quarkus REST formerly RESTEasy Reactive , ArC and Transaction for example. It works by capturing those contextual values that used to be in thread-locals, and restoring them when your code is called. We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example. The solution is located in the context-propagation-quickstart directory. If you are using Mutiny the quarkus-mutiny extension , you just need to add the quarkus-smallrye-context-propagation extension to enable context propagation. With this, you will get context propagation for ArC, Quarkus REST and transactions, if you are using them. This section uses Mutiny reactive types.

Contexts and Dependency Injection

In this example, we will show how to use the ServletContext in a REST Application. One challenge is that you cannot @Inject the ServletContext directly as you would do it in a . .

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