When designing an enterprise solution, one of the primary tasks is to divide your application into separate components that interact with each other. To avoid all the hassle of managing our components, their dependencies, and their life cycles, the contexts and dependency API (CDI) has been developed to be the backbone of component and dependency management. By components, we mean objects that encapsulate your application's business logic. By dependencies, we mean commonly used application-shared resources such as a database connection, user sessions, web service endpoints, and such.

In Chapter 2, Dependency Injection Using CDI 2.0, we'll learn how to create and use CDI beans, how to use bean scopes, how to provide different implementations of the same bean, and how to inject beans into other beans. Moreover, we'll learn about some more advanced topics, such as producers, interceptors, and events.

The data access layer is the most fundamental part of any enterprise application. A common problem arises when dealing with a relational database from an object-oriented system—all runtime data are represented as objects, where the real data is stored as rows in tables. The Java Persistence API (JPA) provides Java developers with all the required operations, mappings, and techniques for mapping objects to the relational database.

In Chapter 3, Accessing the Database with JPA 2.1, we'll learn how to create and use JPA entities and map them to tables and columns. Moreover, we'll learn how to perform the four CRUD operations: mapping entity relationships, using the JPA Query Language and the Criteria API, and mapping inheritance relationships.

Validating your application's data is a required step before any of your business operations. Jakarta EE provides the Java Validation API, which integrates well with other APIs, like JPA and JAX-RS. With this API, you can declare all your validation rules to be processed automatically for you, whenever you receive new data from the user. It's as easy as annotating your domain objects with the appropriate annotation.

In Chapter 4, Validating Data with Bean Validation 2.0, we'll learn how to use the Java Validation API to perform programmatic and automatic bean validation, how to validate graphs of objects in a bean, and the different validation constraints available. Moreover, we'll learn how to validate bean method parameters and return values, and how to define custom validation constraints to handle more complex and recurrent validation scenarios.

The core composing components of an enterprise application in Jakarta EE are Enterprise JavaBeans. They are plain Java objects with embedded business logic, supported by different services from the business tier, such as remoting, transaction management, user session management, timer services, and more.

In this book, we'll learn what enterprise Java beans are, what are they used for, and what services they provide for your embedded business code. We'll study and practice the three available types of sessions bean: stateless, stateful, and singleton.

RESTful services are a key technology for making computer systems talk to each other and, more specifically, making application frontends talk to their backends, and sometimes to other third-party integrations. They are functions that are deployed on a server and can be called remotely from any other system. RESTful is not just another protocol for remoting with HTTP; it's a full architectural style used to build your enterprise applications and make them extensible by other modules or separate systems.

In Chapter 5,  Exposing Web Services with JAX-RS 2.1, we will learn what RESTful services are and how to create your own RESTful services using JAX-RS. Moreover, we'll learn how to use Postman to test your RESTful services. JAX-RS topics such as accepting and processing user parameters, producing JSON responses, and uploading files are all covered in this chapter. In the final section, we'll learn about the newly introduced support for server-sent events in JAX-RS and look at examples of how to use it to provide your clients with on-demand real-time notifications about different business events.

As JSON is a very common format for exchanging data in REST operations, the need for a native API in Java to perform advanced processing over JSON has arisen. Finally, Jakarta EE was introduced?

In this book, we'll get an introduction to the newly introduced API, the JSON Binding API, and see how we can use it to directly manipulate JSON in advanced contexts with practical examples.

Software-to-software messaging is another model of how software communicates with each other. In this model, a messaging middleware stands in the middle of a sender and a receiver to enable the reliable exchange of messages even if one of the two parties is out of service. Moreover, this model enables the application of scaling techniques such as load balancing and message broadcasting to subscribed components.

In this book, we'll learn the basic principles of messaging and how the JMS API provides a comprehensive framework to build a full-featured messaging system to realize the described messaging model. We'll also learn the difference between the two messaging models—Point-to-Point (P2P) and the Publish-Subscribe model—and how to implement both of them, with examples, using the JMS API.

Software-to-user communication is also essential in any enterprise application. Software needs to mail its users about notifications, updates, changes, password change confirmations, and so on. Although in a large-scale development, a separate third-party cloud mailing solution would be a good idea, it's still very common to directly use the mailing APIs to communicate with our users, especially in small-scale developments.

In Chapter 8, Sending Mails with JavaMail 1.6, we'll get a brief introduction to the main mailing protocols. After that, we'll learn and practice how to programmatically send plain text and HTML emails, in addition to optionally attaching files to your emails.

WebSockets is one of the major overall advancements in HTTP communication. It extends HTTP to allow it to handle one or more full-duplex communication channels over a single HTTP connection, enabling all kinds of applications with real-time communication requirements to appear on the web market, such as chatting, multi-player gaming, collaborative document editing, and many more.

In Chapter 8, Sending Mails with JavaMail 1.6, we'll learn what WebSockets are and when to use them. Moreover, we'll learn and practice how to create WebSockets endpoints in Java and how to create a client for them in JavaScript. In addition, we'll learn how to maintain and encode user state in our server. At the end of the chapter, we'll look at a complete example of using WebSockets to implement a cinema tickets booking interface for our book's project.

Authentication and authorization are the most important aspects of any middleware solution. Any enterprise application should provide a way to authenticate users before letting them in and should also check their authorization before availing any functionality to them.

Although JACC and JASPIC have existed since the early days of Java EE, they have gotten more complicated as a result of their continuous evolution. The need to restructure the Security API was a priority request by Java EE developers over the years and, therefore, the Java Security API 1.0 was introduced in Jakarta EE 8.

In Chapter 9, Securing an Application with Java Security 1.0, we'll learn the concepts and terminology related to this new API and how to get started with it by creating a simple login example. Moreover, we'll take a more in-depth look at basic concepts, such as identity stores, authentication context objects, and authentication mechanisms.