Spring Overview
Spring is an application framework. Its inversion of control containers let you create any type of Java application. Spring also has extensions that allow you to build web applications. You can use any Java application that uses the framework, but you can also use it for web applications. Here is an overview of its features. It is easy to learn and use.
Abstract Objects (AOP)
Abstract objects, as the name implies, are classes that provide interfaces that allow you to perform operations on objects. These classes can be of two types: static or dynamic. These types provide similar functionality and can be used in a similar way. The difference between abstract and concrete objects is that the latter cannot access methods that are outside of the interface.
The Factory Pattern
The Factory pattern is an example of this design pattern. Spring already includes an implementation of this design pattern in the framework's BeanFactory class. This pattern allows developers to reuse an interface, reduce copy-paste bugs, and avoid the need to create a class in several places.
Data Access Layer
When developing a Spring application, you should pay attention to the Data Access Layer, or DAO. This is the part of the application that stores data. Most applications are backed by a data store, and the more complex your application is, the more code will need to be placed in the Data Access Layer.
The DAO Pattern
The DAO pattern is a design pattern for implementing persistence for a data-driven application. It describes the structure and behavior of the data access layer. Repositories implement this pattern. In Spring, this means that a repository is an abstraction layer between the database and client code. A repository is usually implemented by a repository, which is a class with an interface that defines the data access layer.
The JPA Framework
The JPA framework enables developers to reduce the amount of code in their data-access layer and simplify their development process. It uses a Query DSL to define a data-access contract. The framework then inspects this contract and builds the interface implementation for developers.
Application Availability State
The application availability state is an attribute of a Spring application. It determines whether the application is ready to receive and serve requests. It is necessary to set this attribute when an application starts. If the application is not ready, the manager should not route traffic to it. When an application is not ready, it can break. If this happens, the container manager should take appropriate action.
Bean Scopes
In addition to the default bean scope, Spring allows you to create custom scopes for your bean instances. For instance, if you want a bean instance to live for the lifetime of an HTTP request, you can use the request scope. But if you want a bean instance to live for the lifecycle of an entire ServletContext, you can use the session scope.
A container can have as many as 20 bean instances. The Singleton scope, on the other hand, forces Spring to produce only one bean instance per container. This means that any change in the state of one instance won't affect the other instances.
@ComponentScan Annotation
When writing Spring code, you need to include the @ComponentScan annotation. This annotation lets you specify which classes and packages Spring should scan. You can use it to specify a bean class or a package name for a component. However, you cannot use a class annotated with @Controller as a Spring controller.
To use the @ComponentScan annotation, annotate a class that contains the property "component" as well as any dependencies it contains. The annotation will automatically add the bean to the application context. Generally, there are four types of annotations for a Spring component. The first one, @Component, is a stereotype of a class. The second is @RequestMapping, which identifies a controller managed by Spring. Finally, there is the @RestController annotation, which merges the @Controller and @ResponseBody annotations to create a RESTful service.
Annotations in Spring
Annotations are popular concepts in Spring. In fact, you might find yourself answering questions about annotations on the Spring professional certification exam. For example, the @ComponentScan annotation has many uses and is useful for detecting bean instances. The annotation provides context-aware dependency injection, which means that Spring will automatically detect annotated classes. Annotation-driven dependency injection is a major feature of Spring 2.0. Spring will recognize a bean automatically if it has a classname containing an @ComponentScan annotation.
