Spring WebFlux framework introduces a new functional web framework built using reactive principles. This is commonly referred to as URI Templating. Because of its popularity, interview questions from 2.
DispatcherServlet in web. Reference Documentation for one of the best frameworks in Java. Spring Framework Version 1. Logging in the GAC, you will need to specify the fully qualified name of the assembly, i. Proxying interfaces 9. Proxying classes 9. Using global advisors 9. Concise proxy definitions 9. The question is now, where does your UserDao get its dataSource dependency from? The naive approach would be to simply create a new DataSource through a constructor, every time you need one.
Unfortunately, that method also needs a DataSource to work with. You would then have another similar method or extract a helper class that contains your DataSource. Consider that a DataSource opens up a real, socket connection from your Java program to your database. This takes time and is rather expensive.
It would be much nicer if we opened just one DataSource and re-used it, instead of opening and closing tons of them. One way of doing this could be by saving the DataSource in a private field in our UserDao, so it can be reused between methods - but that does not help with the duplication between multiple DAOs. To accommodate these issues, you could think about writing a global Application class, that looks something like this:.
Your UserDAO does not have to construct its own DataSource dependency anymore, instead it can ask the Application class to give it a fully-functioning one. Same for all your other DAOs. If your program gets bigger, and you get more and more dependencies, you will have one monster Application.
Instead of actively calling Application. Whenever a caller creates a new UserDao through its constructor, the caller also has to pass in a valid DataSource. From the UserDao perspective this reads much nicer. It only announces to the world "if you want to construct i. But imagine you now want to run your application. Hence, the issue is that you, as a programmer are still actively constructing UserDAOs through their constructor and thus setting the DataSource dependency manually.
That someone is a dependency injection container and is exactly what Spring framework is all about. The Confident Spring Professional. If you want to easily get a deep and practical understanding of the entire Spring Ecosystem or simply refresh your Spring knowledge: I have written a course for you.
As already mentioned at the very beginning, Spring Framework, at its core, is a dependency injection container that manages the classes you wrote and their dependencies for you see the previous section.
That someone , who has control over all your classes and can manage them appropriately read: create them with the necessary dependencies , is called ApplicationContext in the Spring universe. What we want to achieve is the following code I described the UserDao and DataSource in the previous section, go skim it if you came right here and skipped it :.
Here we are constructing our Spring ApplicationContext. The ApplicationContext can give us a fully configured UserDao, i.
What you really want to pass into the ApplicationContext constructor, is a reference to a configuration class, which should look like this:. You have a dedicated ApplicationContext configuration class, annotated with the Configuration annotation, that looks a bit like the Application. You have a method that returns a DataSource and is annotated with the Spring-specific Bean annotation.
You have another method, which returns a UserDao and constructs said UserDao by calling the dataSource bean method. There are many ways to construct a Spring ApplicationContext, for example through XML files, annotated Java configuration classes or even programmatically. To the outside world, this is represented through the single ApplicationContext interface. Look at the MyApplicationContextConfiguration class from above.
It is a Java class that contains Spring-specific annotations. That is why you would need to create an Annotation ConfigApplicationContext. There are also many others, but in a modern Spring application, you will usually start out with an annotation-based application context. For now, there is one method that knows how to construct UserDao instances and one method that constructs DataSource instances.
These instances that those factory methods create are called beans. It is a fancy word for saying: I the Spring container created them and they are under my control.
But this leads to the question: How many instances of a specific bean should Spring create? How many instances of our DAOs should Spring create?
To answer that question, you need to learn about bean scopes. Or per HttpSession? Or per WebSocket? You can read up on a full list of available bean scopes here , but for now it is suffice to know that you can influence the scope with yet another annotation. The scope annotation controls how many instances Spring will create. The gist: Most Spring applications almost entirely consist of singleton beans, with the occasional other bean scope prototype, request, session, websocket etc.
So far, you explicitly configured your beans in your ApplicationContext configuration, with the help of Bean annotated Java methods. Just a quick recap of what this looks like:. One question: Why do you have to explicitly call new UserDao with a manual call to dataSource? Cannot Spring figure all of this out itself?
What this ComponentScan annotation does, is tell Spring: Have a look at all Java classes in the same package as the context configuration if they look like a Spring Bean! This means if your MyApplicationContextConfiguration lives in package com.
How does Spring know if something is a Spring bean? Easy: Your classes need to be annotated with a marker annotation, called Component. This tells Spring, similarly to that Bean method you wrote before: Hey, if you find me annotated with Component through your ComponentScan, then I want to be a Spring bean, managed by you, the dependency injection container!
Should there be no DataSources configured in any of your Spring configurations, you will receive a NoSuchBeanDefinition exception at runtime.
I have been lying to you a tiny bit in the previous section. AOP aims to provide more modularity to the cross-cutting concerns, which are functions that span across the application, such as:. Moreover, AOP complements object-oriented programming by providing a different way to structure the program, where OOP modularity is based on classes. In AOP, the main unit of modularity is an aspect cross-cutting concern. This enables users to use AOP to create custom aspects and declarative enterprise services.
The IoC container does not depend on AOP, offering further freedom for developers to select their preferred programming method. Database communication issues are one of the common issues developers face when developing applications. Additionally, it offers features such as resource management, exception handling, and resource wrapping for all the supported data access frameworks, further simplifying the development process.
Spring offers an abstraction mechanism for Java that enables users to:. This enables developers to create feature-rich transactional systems that span across the applications without depending on EJB or JTA. It is a request-based framework that allows developers to easily create customized MVC implementations that exactly suit their needs.
The core component of Spring MVC is the DispatcherServlet class which handles user requests and then forwards them to the correct controller. This allows the controller to process the request, create the model and then provide the information to the end-user via a specified view. This Spring Web Service component provides a streamlined way to create and manage web service endpoints in the application.
It offers a layered approach that can be managed using XML and can be used to provide mapping for web requests to a specific object. Testing is a core part of any development. Spring simplifies testing within the framework with components like:. Read about test automation frameworks. The above diagram represents the basic components of the Spring architecture.
As you can see, Spring is built using different modules that enable different functionality. This includes the modules that are used to handle data access and transaction processing in an application. First, we need Java installed on our PC.
Spring Boot is an extension of the Spring framework that enables users to create standalone Spring-based applications with minimal dependencies. I was able to stream line this by using the built in support in Spring with it's ResourceHttpMessageConverter. This will set the content-length and content-type if it can determine the mime-type.
Remember to do response. With Spring 3. If you use this, then your controller does not need a HttpServletResponse object, and therefore it is easier to test.
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