BOOKS FOR PROFESSIONALS BY PROFESSIONALS® Layka Learn Java for Web Development RELATED Web development is still one of today’s most popular, active, and important programming and development activities. From a single web page to an e-commerce-enabled web site to a fully-fledged web application, the Java programming language and its frameworks allow you great flexibility and productivity for your web application development. Learn Java for Web Development teaches web developers who are new to Java key skills, Java-based languages, and frameworks to build simple or complex web sites and applications. As soon as you pick up this book, Vishal Layka’s experience guides you on a very practical learning and building journey. You will learn the Java nuts and bolts necessary to build a simple “HelloWorld” application, as well as a “HelloWorld” Java-based web application using servlets and JavaServer Pages (JSPs). Using a real-word case study (a bookstore e-commerce application), you next will learn more about servlets and JSPs, add JavaServer Faces (JSFs), and explore the JSP and JSF expression languages. Then you’ll build your web application using Apache Struts2 and the Spring MVC framework. The book concludes by examining industry best practices and how these might fit with your bookstore web application, as well as covering alternative Java Web frameworks like Groovy/Grails and Scala/Play 2. You also can explore the basics of Java, Groovy, and Scala in the book’s appendices. With Learn Java for Web Development, you will see all these key technologies in action and form a solid foundation for web development with Java and Java-based technologies. Shelve in ISBN 978-1-4302-5983-1 53999 Programming Languages/Java User level: Beginning–Intermediate SOURCE CODE ONLINE 9781430259831 www.apress.com For your convenience Apress has placed some of the front matter material after the index. Please use the Bookmarks and Contents at a Glance links to access them. Contents at a Glance About the Author ����������������������������������������������������������������������������������������������������������������xv About the Technical Reviewer ������������������������������������������������������������������������������������������xvii Introduction �����������������������������������������������������������������������������������������������������������������������xix ■ Chapter 1: Introducing Java Web Development�����������������������������������������������������������������1 ■ Chapter 2: Building Web Applications Using Servlets and JSP ���������������������������������������43 ■ Chapter 3: Best Practices in Java EE Web Development �����������������������������������������������105 ■ Chapter 4: Building a Web Application Using Struts 2 ��������������������������������������������������161 ■ Chapter 5: Building Java Web Applications with Spring Web MVC �������������������������������203 ■ Chapter 6: Component-Based Web Development Using JSF 2 ��������������������������������������263 ■ Chapter 7: Rapid Web Development with Grails ������������������������������������������������������������299 ■ Chapter 8: Play with Java and Scala �����������������������������������������������������������������������������355 ■ Appendix A: Introduction to Java ����������������������������������������������������������������������������������383 ■ Appendix B: Introduction to Groovy �������������������������������������������������������������������������������399 ■ Appendix C: Introduction to Scala ���������������������������������������������������������������������������������423 Index ���������������������������������������������������������������������������������������������������������������������������������435 v Introduction This book is for a large cross section of modern Java web developers, with various levels of experience. Learning the Java programming language is a noble cause, but learning merely the Java language is not enough in the real world. Java developers have to learn Java EE, a collection of related server-side technologies, to put their Java skills to any real use. But learning Java EE is not enough either. The Java language along with Java EE may suffice to develop web applications for projects in the same organization, as a means to reusability, but the diverse landscape of Java on the Web is permeated with several web frameworks, such as Spring Web MVC, that make development much easier; thus, a Java web developer has to have the knowledge of these web frameworks. But this is not enough still. In the very first line of this introduction, I mentioned that this book is for a modern Java web developer. Modern Java is more than just a language; it is now a fully optimized platform because several other languages such as Groovy and Scala, called the JVM languages, now run on the Java Virtual Machine (JVM). All such JVM languages, especially Groovy, have a close association with Java, and you will come across web applications before long where Java and these other JVM languages work in tandem. The most ambitious projects will require you to build web applications using these JVM languages. This book addresses all the needs of a modern Java web developer. It is designed for beginners up to intermediate developers and explains the specifics of Java on the Web. For example, this book is perfect for developers who are aware of technologies like MVC but do not yet understand how and why they have changed the way web applications are built. This book is also for developers who want to learn frameworks other than JSF 2 (which is bundled with Java EE). This book covers four types of web frameworks: request based, component based, rapid, and reactive. Among these four types, the book covers five proven web frameworks: Struts 2, Spring Web MVC, JSF 2, Grails 2, and Play 2. In addition, this book is for developers who have no experience in the Java, Groovy, and Scala programming languages but who yearn to create web applications. This book provides the essentials of these three languages in the appendixes. xix xx Introduction Instead of simply pronouncing one web framework the best, Learn Java for Web Development shows the strengths of the most popular web frameworks by means of a real-world bookstore application. Developing a complete real application necessitates a seamless collaboration of dynamic functionalities, and the code for building such components is contrived and too involved. Instead of focusing on developing such moving parts, this book confines its attention on leveraging the strengths of each web framework. How the Book Is Structured The book consists of eight chapters, which I’ll describe next, plus the three previously mentioned appendixes that introduce the Java, Groovy, and Scala languages. Chapter 1: Introducing Java Web Development Chapter 1 explains the main objective that shapes this book and highlights what appears in the subsequent chapters. This chapter begins with a discussion of a significant change in the Java landscape, its implication, and what Java exactly means today. The chapter then discusses the three key players that join forces in building modern Java web applications: the JVM languages, Java EE, and the Java web frameworks. This chapter introduces the key features of a modern Java web application such as Ajax and REST, WebSocket for real-time web application, the Typesafe stack for a reactive web application, and client-side MVC frameworks for responsive and single-page web applications. Finally, the chapter introduces some important aspects of modern web development that are beyond the scope of this book, such as Java information retrieval on the Web, and briefly introduces the central component of Web 3.0, which is still an open subject of research, the Semantic Web. Chapter 2: Building Web Applications Using Servlets and JSP Chapter 2 begins with a discussion of the evolution and architecture of web applications. The chapter then highlights how to use the standard web API. The first pass at the sample application uses only servlets and JSP. Then the chapter shows you how to build the same application as a Model 2 application. Chapter 3: Best Practices in Java EE Web Development Chapter 3 examines the chain of causality that leads to the need for following best practices. The chapter explains the need to evolve projects and introduces Expression Language and JSTL. The chapter then discusses the Java EE web tier patterns. Chapter 4: Building a Web Application Using Struts 2 In Chapter 4, you’ll learn about Struts 2. Not as popular as it used to be, Struts 2 is introduced in this book for developers who have to maintain legacy applications. This chapter first introduces the key architectural components of Struts 2. Then you will learn to develop your first application using Struts 2 and Maven 4. Moving forward, you will learn to develop the bookstore application and integrate with Tiles 3. Introduction xxi Chapter 5: Building Java Web Applications with Spring Web MVC Chapter 5 explains three key objectives of the Spring Framework: loose coupling using dependency injection, dealing with cross-cutting concerns using AOP, and removing boilerplate code using Spring templates. Elucidating how Spring 3 works, the chapter introduces the Spring Web MVC architecture. Then you will learn to build your first web application using Spring 3 Web MVC. This chapter also shows you how to build the bookstore application. You will learn to use the latest version of the SpringSource tool suite. Chapter 6: Component-Based Web Development Using JSF Chapter 6 introduces you to a component-based framework called JSF 2 that is bundled with Java EE. After you have familiarized yourself with the request-based framework presented in Chapter 4 and Chapter 5, understanding JSF 2 will be much easier. This chapter shows you how JSF 2 represents a paradigm shift in web development and introduces you to key components of the JSF 2 architecture. After you have a firm grasp of the architecture components, this chapter shows you how to develop your first JSF 2 application, and along with this you will learn the life-cycle phases of a JSF 2 application. Then the chapter shows you how to integrate JSF 2 with the Spring Framework so that you can access the database via Spring templates from the JSF 2 web layer. Finally, the chapter shows you how to develop the bookstore application. Chapter 7: Rapid Web Development with Grails Grails is a rapid application development framework that lets you create web applications in record time. Chapter 7 introduces you to two techniques of generating web applications with Grails: static and dynamic scaffolding. The chapter then takes you through the code generated and explains step-by-step how the code works. Having presented the code generated, this chapter shows you how to develop the bookstore application with Grails 2. This chapter also covers unit testing, an oft-neglected task in application development. This chapter shows you how to build tests for your web applications using the JUnit testing framework. Then this chapter shows you how to use the in-memory database H2. In this chapter, you will also learn to use the latest version of the Groovy-Grails tool suite. Chapter 8: Play with Java and Scala Chapter 8 introduces the key web player of the Typesafe stack, the Play 2 framework, and explains how the Typesafe stack provides an alternative to Java EE to build Java- and Scala-based applications. First you will learn to develop a Java-based web application using Play 2. Then you will learn to develop a Scala-based web application using Play 2. Subsequently, this chapter shows how to use the model and access a database in Play 2. 1 Chapter Introducing Java Web Development The mind, once stretched by a new idea, never returns to its original dimensions. —Ralph Waldo Emerson An intelligent machine is that which extends the very imagination with which it was built. An example of this is the instruction called invokeDynamic,1 which was introduced with Java 7 to optimize the performance of dynamically typed languages on the Java Virtual Machine (JVM). The JVM, originally intended for Java, can now host a myriad of programming languages, including Groovy2 and Scala.3 This has led to a renaissance of Java web development. This new paradigm of cross-pollination and diverse, well-founded options carves out a number of niches in the Java ecosystem, resulting in a richer web landscape than ever before. The open source community has capitalized on the multiparadigm capabilities offered by the languages that run on the JVM, by means of web frameworks, to dramatically enhance the productivity in web development. Java EE4 advanced this momentum, pioneered by Java frameworks such as Spring,5 by standardizing and improving the API and runtime environment. Further, functional programming constructs, in the form of lambdas, have been added to Java 8. As a result, Java is on the rebound to become an übersolution. This chapter sets the stage for the book by introducing the three key players that join forces in building modern Java web applications: the JVM languages, Java EE, and the Java web frameworks. 1http://cr.openjdk.java.net/~jrose/pres/200910-VMIL.pdf 2http://groovy.codehaus.org/ 3www.scala-lang.org/ 4www.oracle.com/technetwork/java/javaee/overview/index.html 5http://spring.io/ 1 2 CHAPTER 1: Introducing Java Web Development Note The JVM languages represent a new category of languages that run on the JVM. With the latest version, Java 8, Java is no longer a privileged JVM language and is now simply one of the many languages that run on the JVM. The chapter begins by introducing the JVM languages and then introduces Java EE. The Java EE platform is the set of API specifications that act as the building blocks for developing web applications. The chapter then highlights the Java web frameworks, which will be the subject of the book from Chapter 4 onward. JVM Languages The JVM is the runtime environment that provides you with the ability to use different programming languages for building web applications. The JVM languages can be largely classified into two types: languages that are designed for the JVM and existing languages that are ported to JVM. Languages Designed for the JVM Plenty of languages are specifically designed for the JVM; Table 1-1 describes a few of them. All but Clojure are discussed in this book. Table 1-1. Languages Designed for the JVM Language Designed for JVM Description Clojure6 Clojure is a dynamically typed, functional language. Groovy Groovy is a dynamic, compiled language with syntax similar to Java but is more flexible. Java Java is a statically typed, imperative language. The latest release of Java, Java 8, supports aspects of functional programming. Scala Scala is a statically typed, compiled language that supports aspects of functional programming and performs a large amount of type inference, much like a dynamic language. Here are some important definitions:  Dynamic typing: Dynamic typing keeps track of information about what sort of values the variables contain by carrying the type information on the values held in variables.  Static typing: In static typing, the type information is all about the variables, not the values in them. 6http://clojure.org/ CHAPTER 1: Introducing Java Web Development 3  Imperative languages: These are languages in which the state can be mutated by the instructions in the language.  Functional languages: In functional languages, the functions operate on values as in procedural languages, but instead of mutating the state, the functions are purely mathematical functions that return new values. Figure 1-1 shows where Java 8, Groovy, Scala, and Clojure fall on the functional language continuum. Java 8 introduces lambdas, which makes it slightly functional, Groovy has had functional constructs since its inception and is even more functional with Groovy 2.0, and Scala is the most functional of the three object-oriented (OO) languages. Clojure, on the other hand, is a purely functional, non-OO language. Figure 1-1. Functional gradation of JVM languages Note In Figure 1-1, no version number is mentioned for Groovy, Scala, and Clojure because Java supports aspects of functional programming starting from Java 8 only. Languages Ported to the JVM JRuby, Jython, and Rhino are a few of the mainstream JVM implementations of existing languages. Table 1-2 describes them. 4 CHAPTER 1: Introducing Java Web Development Table 1-2. Languages Ported to the JVM Languages Ported to JVM Description JRuby7 JRuby is a JVM reimplementation of the Ruby programming language. Ruby is a dynamically typed OO language with some functional features. Jython8 Jython is a reimplementation of Python on the JVM, so it is a dynamic language. Rhino9 Rhino provides an implementation of JavaScript on the JVM. JavaScript is a dynamically typed OO language. This book is based on some of the mainstream object-oriented JVM languages that were specifically designed for the JVM, namely, Java, Groovy, and Scala. Java EE Java began life as a programming language designed for building stand-alone applications and grew rapidly into other spheres. A large part of Java’s popularity can be attributed to its usage in creating web applications. A web application consists of static and dynamic (interactive) web pages. Static web pages contain various types of markup languages (HTML, XHTML, and so on) and are used, in general, to provide information; dynamic web pages, on the other hand, are capable of generating content with the aid of additional web components (covered in Chapter 2). Thus, a web application is a collection of web pages and is capable of generating dynamic content in response to requests. Unlike a web page used merely to provide information, a web application lets you perform some activity and save the result. Developing a web application, however, is fundamentally different from building stand-alone applications and requires you to understand the following three key elements:  The Java EE platform: This is the set of API specifications that are the building blocks of the web application.  The web container: The web container implements the API specifications of the Java EE platform. Specifically, the web container provides the services for managing and executing web components such as servlets, JSPs, filters, listeners, and render responses to the client. The web containers are covered in Chapter 2. Note There are several types of containers, but this book will focus on the web container primarily used for web applications. You have to choose the container based on the kind of application you want to develop.  Web components: These are hosted by the container. These web components, such as servlets, JSPs, filters, and listeners, are covered in Chapter 2. 7http://jruby.org/ 8www.jython.org/ 9https://developer.mozilla.org/en-US/docs/Rhino_documentation