Head over to Leanpub to grab a PDF version of this book
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 API for WebSocket: a Java based standard (specification) for building WebSocket based applications. As with most standard (Java) APIs, the WebSocket API has multiple (competing) implementations which comply with the specification. It is also a part of the Java EE Platform.
What it implies is that you can use this standard API in a standalone format as well as part of a larger platform in concert with other Java EE based APIs such as JAX-RS, CDI, JPA, EJB, JMS etc.
What's in the book ?
Let's look at a quick outline of book contents
The first three lessons are meant to get your feet wet