The content of this book are divided into distinct sections which cover the bare basics, core components and some of the advanced framework features as well. Here is a snapshot

• JAX-RS 2.1 (latest addition) - Server Sent Events, JSON-B integration, Reactive Client API etc.
• Core: resources, annotations, HTTP method dispatch, injection
• Providers: message body readers & writers, filters, interceptors, exception mappers
• Advanced: request processing pipeline, method matching, caching, content negotiation
• Other topics: Asynchronous processing, Client API, Security

The book is what it says it is - a handbook, a quick reference, a fast track guide. It covers the nitty gritty of the Java WebSocket API which is a standard (specification) for building WebSocket applications. It is targeted (primarily) towards Java/Java EE developers and can be used in various capacities

• As a getting started with the Java WebSocket API guide
• You are already well versed with this API and its constructs, but need a quick peek/reference to a specific API, it's usage, nuances etc.
• Maybe you're just curious about what Java has to offer in terms of WebSocket support - feel free to check this out

The first three lessons are meant to get your feet wet

• Warm up
• API Overview
• Programming Model

Then comes the core part which is important from a API usage perspective

• Sending Messages
• Receiving Messages
• WebSocket Client API

The default conventions offered by the WebSocket API can actually hide the details related to Configuration & Deployment, but you should know them anyway ! 

• Configuration
• Deployment

The book ends with a exploration of how the API integrates with other Java EE specifications as well as a quick peek into the threading details of some of the API constructs

• Tying in with the Java EE Platform: Part I (EJB, CDI) and II (Servlet, Security)
• Lifecycle and Concurrency semantics

It is not meant to be ...

• a generic discourse on WebSocket: it deals with the Java implementation of the WebSocket specification (JSR-356 to be specific)
• a deep dive into the WebSocket RFC
• exploration of other Java based WebSocket APIs/frameworks (e.g. Atmosphere etc.) is not the goal of this book