The Java EE platform includes the Java API for WebSocket (JSR 356), which enables you to create, configure, and deploy WebSocket endpoints in web applications. The WebSocket client API specified in JSR 356 also enables you to access remote WebSocket endpoints from any Java application.
The Java API for WebSocket consists of the following packages.
The javax.websocket.server package contains annotations, classes, and interfaces to create and configure server endpoints.
The javax.websocket package contains annotations, classes, interfaces, and exceptions that are common to client and server endpoints.
WebSocket endpoints are instances of the javax.websocket.Endpoint class. The Java API for WebSocket enables you to create two kinds of endpoints: programmatic endpoints and annotated endpoints. To create a programmatic endpoint, you extend the Endpoint class and override its lifecycle methods. To create an annotated endpoint, you decorate a Java class and some of its methods with the annotations provided by the packages mentioned previously. After you have created an endpoint, you deploy it to an specific URI in the application so that remote clients can connect to it.
Note:
In most cases, it is easier to create and deploy an annotated endpoint than a programmatic endpoint. This chapter provides a simple example of a programmatic endpoint, but it focuses on annotated endpoints.
The process for creating and deploying a WebSocket endpoint follows.
Create an endpoint class.
Implement the lifecycle methods of the endpoint.
Add your business logic to the endpoint.
Deploy the endpoint inside a web application.
The process is slightly different for programmatic endpoints and annotated endpoints, and it is covered in detail in the following sections.
Note:
As opposed to servlets, WebSocket endpoints are instantiated multiple times. The container creates an instance of an endpoint per connection to its deployment URI. Each instance is associated with one and only one connection. This facilitates keeping user state for each connection and makes development easier, because there is only one thread executing the code of an endpoint instance at any given time.
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