Monday, November 24, 2014

Book Review: RESTful Java Patterns and Best Practices

Bhakti Mehta's RESTful Java Patterns and Best Practices was recently published by Packt Publishing. Consisting of six chapters and an appendix spanning approximately 125 substantive pages, its subtitle is, "Learn best practices to efficiently build scalable, reliable, and maintainable high performance RESTful services."


The Preface of RESTful Java Patterns and Best Practices begins with a description of why REST is important today. It includes several short summaries of each of the book's chapters. The Preface explains that Maven 3 and GlassFish 4 are required to build and run the book's examples and states that the book is designed as "a perfect reading source for application developers to get familiar with REST."

Chapter 1: REST – Where It Begins

RESTful Java Patterns and Best Practices's initial chapter provides a single paragraph on SOAP/WSDL-based web services before turning attention to REST-based web services. The basic characteristics of and increased "-ilities" provided by REST are described. The Richardson Maturity Model is also examined in some detail. I'm not sure that the Richardson Maturity Model clears things up or muddies them by encouraging interchangeable use of the terms HTTP and REST.

The first chapter includes brief descriptions of the characteristics of safe methods and of idempotent methods and describes which HTTP methods fit each category. The chapter then lists several "design principles for building RESTful services" before describing each in greater detail. This is section provides a brief and highly readable introduction to the basics of REST.

Chapter 1's introduction of the Java API for RESTful Web Services (JAX-RS) includes simple examples of turning POJOs into REST resources using JAX-RS annotations such as @GET, @POST, @Path, @Produces, @Consumes, and @ValidateOnExecution.

Chapter 1 provides a nice introduction to the Client API that is new to JAX-RS 2.0. It also briefly discusses some other approaches one can use to communicate and work with REST-based services: curl, Postman on Chrome, Advanced REST Client for Google Chrome, and JSONLint. Both curl and Postman get extra attention including a color screen snapshot of Postman in the electronic edition I reviewed.

The first chapter concludes with a bullet-format list of "best practices when designing resources," a list of related online resources, and a Summary. Overall, this first chapter is a nice high-level introduction to REST and to Java's approach to REST via JAX-RS. The code examples are simple and short and easy to understand. Just enough detail is provided to get a feel for REST and JAX-RS.

Chapter 2: Resource Design

Chapter 2 of RESTful Java Patterns and Best Practices delves more deeply into HTTP and REST concepts such as content negotiation (including contrasting use of HTTP headers versus URL patterns), alternative resource representation (MessageBodyReader and MessageBodyWriter, StreamingOutput, and ChunkedOutput), Jersey's JSON support (ObjectMapper, @XMLRootElement, JsonArray, and JsonObject), API versioning (comparing URI, request query parameter, and Accept header approaches), HTTP response codes, and the JAX-RS classes Response and ResponseBuilder.

The second chapter provides greater details regarding application of JAX-RS to REST-based application implementation. The examples are relatively short and clear and illustrate well the points being made.

Chapter 3: Security and Traceability

The third chapter opens up with two paragraphs explaining why security and traceability are important in today's REST-based applications. The specific security and traceability topics discussed in this chapter are logging in REST-based applications, exception handling in REST-based applications, validation patterns, and federated identity.

The section on logging from a REST-based application demonstrates writing of a servlet filter (annotated with @WebFilter and implementing Filter) that can log certain metadata about each request as each request occurs. This section also outlines some logging best practices that I'd say are general logging best practices rather than REST-specific logging best practices.

Chapter 3's section on validating services states, "JAX-RS supports the Bean Validation to verify JAX-RS resource classes." The text and accompanying code samples demonstrate use of bean validation with standard annotations such as @ValidateOnExecution, @Valid, and @NotNull and a custom annotation @VerifyValue. This section also demonstrates with code and explanation how to create a custom exception mapper (implementation of ExceptionMapper that "catch[es] thrown application exceptions and write[s] specific HTTP responses.").

Part of Chapter 3 focuses on authentication and authorization. This section introduces Security Assertion Markup Language (SAML) and SAML Web Browser Profile for authentication and OAuth (open authorization) for authorization. This section has some nice graphics (with a bit of color in the PDF version) depicting how authentication with SAML and authorization with OAuth work at a high level.

Chapter 3's coverage or authorization includes more details on characteristics of OAuth 2.0. Access and refresh tokens are covered as is the level of support for OAuth 2.0 provided by Jersey (the Jersey implementation supports client side only and Authorization Code Grant Flow).

The third chapter includes a section titled "Best practices for OAuth [2.0] in the REST API." Although these seem to be generally applicable to use of OAuth whether REST is involved or not, I liked the table presenting different situations and when SAML or OAuth is preferable. There is a very brief section in Chapter 3 that introduces OpenID Connect, which the author describes as "a simple REST- and JSON-based interoperable protocol built on top of OAuth 2.0."

Before concluding with the summary and recommended reading sections typical of chapters in RESTful Java Patterns and Best Practices, the third chapter briefly outlines "REST architectural components" to be covered in more detail later. One "recommended reading" that I found particularly interesting is OAuth 2.0 and the Road to Hell.

Chapter 4: Designing for Performance

RESTful Java Patterns and Best Practices's fourth chapter advertises itself as covering "advanced design principles related to performance that every developer must know when building RESTful services." Discussion of strong and weak HTTP caching headers is preceded by an overview of general caching principles. A code listing and accompanying explanation demonstrate how to specify HTTP caching headers in JAX-RS responses. Similarly, this section also looks at the ETag response-header field and how to apply it to a JAX-RS response. The section of Chapter 4 on caching concludes with a brief description of RESTEasy's extension to JAX-RS caching.

"Asynchronous and long-running jobs in REST" is the second major topic of Chapter 4. This section uses code listings, textual explanations, and sequence diagrams to demonstrate use of JAX-RS 2.0 support for asynchronous processing with constructs such as AsyncResponse, @Suspended, CompletionCallback, ConnectionCallback, InvocationCallback, and Java SE Future interface.

The "Asynchronous resources best practices" section of Chapter 4 briefly describes "best practices when working with asynchronous RESTful resources." These tend to be best practices for working with HTTP asynchronously whether in REST or not.

There is a section in Chapter 4 that discusses dealing with partial updates in a REST application using PATCH, PUT, or POST. This section demonstrates creation of an annotation called @PATCH to annotate JAX-RS methods to be used for patch functionality.

The final section of Chapter 4 of RESTful Java Patterns and Best Practices before its summary and recommended reading section is on JSON Patch. This section provides a brief overview of JSON Patch and provides code listing and explanations of how to use JSON Patch.

Chapter 5: Advanced Design Principles

The promise of RESTful Java Patterns and Best Practices's fifth chapter is to cover "advanced design principles that every developer must know when designing RESTful services." The covered topics are rate-limiting patterns, response pagination, internationalization and localization, REST pluggability and extensibility, and some miscellaneous topics. The section on rate-limiting pagination is relatively lengthy and includes code snippets and discussion as well as an outline of some best practices for reducing and avoiding rate-limiting pagination.

"Response pagination" is covered in the fifth chapter, which looks at three types of response pagination: Offset-based pagination, Time-based pagination, and Cursor-based pagination. The chapter then provides an example of implementing offset-based pagination with JAX-RS.

Chapter 5's section on internationalization and localization describes the setting of localization parameters on HTTP headers, on query parameters, and as part of REST responses. Discussion in this section on runtime content negotiation covers HTTP headers Accept-Language and Content-Language and application of the JAX-RS Variant class.

The "Miscellaneous topics" section of Chapter 5 discusses Hypermedia as the Engine of Application State (HATEOAS), which I believe is one of the most commonly misunderstood and under-appreciated features of REST for those new to REST. This chapter's introduction, which includes examples, is a relatively straightforward and concise introduction to the topic. After introducing HATEOAS, the chapter uses an example of PayPal's REST API support for HATEOAS to illustrate real-world application of HATEOAS.

Another Chapter 5 "Miscellaneous Topic" addresses REST extensibility. This is only covered very briefly (single paragraph) and makes assertions about REST being more maintainable and readable (presumably than SOAP-based web services) with lightly offered justification for these claims. Given how little concrete evidence (and no practical examples) is provided, this section is not very compelling.

Chapter 5 concludes with a brief discussions of topics related to documenting and testing REST-based applications. The most appealing part of this coverage for me was the reference to tools that can be used for testing and documenting REST-based applications. This section introduces REST Assured, which it describes as "the Java DSL for easy testing of RESTful services," and provides a simple illustrative example of this in action. The coverage of Swagger does not illustrate its use, but does describe it as "a language-agnostic framework implementation for describing, producing, consuming, and visualizing RESTful web services."

Chapter 6: Emerging Standards and the Future of REST

Although the Fielding dissertation that codified the REST concept was published in 2000, it continuing rising popularity has meant new developments in understanding and applying of the REST architectural style and in the available related tooling. This chapter begins by describing real-time APIs and describing polling and the disadvantages of polling.

Chapter 6 provides brief explanations of how PubSubHubbub and streaming can each be used to address the limitations of polling. Both of these approaches are explained with text and simple graphics. The section on streaming discusses server-sent events (SSE) and their nonstandard support in Jersey.

RESTful Java Patterns and Best Practices's final chapter also introduces WebHooks, which it defines as "a form of user-defined custom HTTP callbacks." This section uses text description, simple graphics, and coverage of implementing case studies to explain this topic. The WebSockets protocol is also covered in the sixth chapter and is described as "a protocol that provides full-duplex communication channels over a single TCP connection." WebSockets is explained with text descriptions, simple graphics, a table, and a code listing. A couple paragraphs each are also dedicated to introducing (at a conceptual level) XMPP and BOSH over XMPP.

Chapter 6 includes a section with text and a table that compares and constrasts WebHooks, WebSockets, and Server-Sent Events. Chapter 6's section "REST and Micro Services" briefly describes "different advantages of Micro Services as compared to monolithic services."

As is the case with the previous five chapters, Chapter 6 ends with a "Recommended Reading" section and a "Summary." The "Summary" is mostly a summary of the chapter rather than the book, though there is a reference to another book co-authored by this book's author: Developing RESTful Services with JAX-RS 2.0, WebSockets, and JSON. The summary for the overall book is left to the Appendix, which is really just another chapter and which I review later in this post.

The sixth and final chapter of RESTful Java Patterns and Best Practices is a high-level overview of trending considerations for REST-based applications. This chapter has very little Java-specific (or JAX-RS-specific) content.


Although RESTful Java Patterns and Best Practices's table of contents lists six chapters and an appendix, the Appendix feels just like the six chapters. It not only has "Recommended Reading" and "Summary" sections like its preceding chapters, but it even includes text that refers to "this chapter." The chapter/appendix introduces three REST APIs: REST API from GitHub, Open Graph API from Facebook, and REST API from Twitter. For me, the most interesting aspect of these introductions was how the author illustrated some of the patterns covered previously in the book from each covered API's perspective. This provides reinforcement with concrete APIs of some of the previously discussed concepts and patterns.

The Appendix's "Summary" summarizes the appendix and the entire book.

General Observations

  • The code listings in RESTful Java Patterns and Best Practices are black text on white background with no color syntax (even in the PDF version) and no line numbers. Most of the code listings are short enough that color syntax and line numbers are not as important as they otherwise might be.
  • I liked the approach taken in RESTful Java Patterns and Best Practices of presenting small snippets of code to illustrate points being made and referencing the code available for download for additional and context code.
  • There are several illustrative graphics in RESTful Java Patterns and Best Practices, a few of of them with multiple colors in the PDF edition and some of them in grayscale, and many of them black font on white background, even in the PDF edition.
  • There are some typos in RESTful Java Patterns and Best Practices. They're generally minor and I provide some examples here to demonstrate their nature:
    • One sentence states, "JAX-RS 2.0 had newer Client APIs for accessing RESTful resources."
    • The section introducing JAX-RS annotations discusses @PATH when it really should be @Path.
    • The section on JSON and Jersey references JSONArray and JSONObject when JsonArray and JsonObject are intended.
    • The acronym PPI when spelled out only has an opening parenthesis and not a closing parenthesis.
  • I liked how each chapter included a "Recommended Reading" section with several freely available online resources, most of which had been referenced earlier in the chapter.
  • I liked the Appendix's use of three popular REST APIs to illustrate some of the concepts and patterns introduced in the book's six chapters.
  • In some cases, I would have liked to see more Java/JAX-RS implementation details for certain patterns, especially in the sixth chapter.
  • Other reviews of RESTful Java Patterns and Best Practices are available and worth checking out for a more complete overall picture of the book based upon multiple perspectives:


RESTful Java Patterns and Best Practices introduces basic REST concepts, patterns, and practices and how to apply many of those patterns and concepts with JAX-RS. This book is probably best suited for those looking for introductory information on a broad set of considerations pertinent to REST applications and implementing those considerations with Java and JAX-RS. For those seeking more detailed coverage of REST principles and JAX-RS application of those principles, RESTful Java with JAX-RS 2.0 might be more appropriate.

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