1484207149 {100DEFF6} Scripting in Java_ Integrating with Groovy and JavaScript [Sharan 2014-12-04].pdf

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Contents at a Glance

About the Author �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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About the Technical Reviewers �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Acknowledgments �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Introduction �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 1: Getting Started �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 2: Executing Scripts �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 3: Passing Parameters to Scripts�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 4: Writing Scripts in Nashorn �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 5: Procedures and Compiled Scripts �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 6: Using Java in Scripting Languages �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 7: Collections �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 8: Implementing a Script Engine �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 9: The jrunscript Command-Line Shell�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 10: The jjs Command-Line Tool �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 11: Using JavaFX in Nashorn �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 12: Java APIs for Nashorn �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Chapter 13: Debugging, Tracing, and Profiling Scripts �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Index �½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½�½

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Introduction

When I wrote the three volumes of

Harnessing Java 7

in 2012, I did not include a chapter

on the Java Scripting API because of the limited space that I had for each volume. Note

the phrase “Java Scripting,” which uses two separate words: “Java” and “Scripting.”

“JavaScript” is the name of a scripting language, which has nothing to do with the Java

programming language, whereas the phrase “Java Scripting API” is the Java API that lets

Java applications interact with scripting languages.

In the first release, I had titled this book

Harnessing Scripting in Java,

and it covered

only the Java Scripting API and Rhino script engine. The release did not cover the

JavaScript language. JDK 8 ships with a lightweight high-performance JavaScript engine

called Nashorn, which replaces the Rhino engine that shipped with JDK7. This book

covers the JavaScript language completely with comprehensive coverage of the

Nashorn engine.

Learning the Java Scripting API, which was introduced in Java 6, is not essential

for all Java developers, although it is important and very useful if you are familiar with

scripting languages such as Rhino JavaScript, Groovy, Jython, JRuby, and so on and want

to take advantage of those scripting languages in Java applications.

I started learning the Java Scripting API by reading some online blogs and articles;

they were helpful, but not quite comprehensive in giving me a clear and complete picture

of how the Java Scripting API helps Java applications interact with scripting languages.

My next step in the learning process was reading the specification for JSR-223, Scripting

for the Java Platform Specification, along with the Java API documentation for the

javax.script

package. Reading the JSR-233 specification gave me a complete picture of

the Java Scripting API; however, I was not ready to write this book. I was still missing some

pieces of the puzzle. Therefore, I decided to read the source code for the classes in the

javax.script

package. I also read the source code for some scripting languages. Finally,

in the process of learning the API, I developed a simple scripting engine, which I named

JKScript. Finally, I read the ECMAScript 5.1 specification to get a complete picture of the

JavaScript language itself. The main difficulty that I faced in writing this book was getting

the information on the Nashorn engine and its features. A Wiki is maintained at

https://wiki.openjdk.java.net/display/Nashorn/Main,

which provides information

about the Nashorn engine in bits and pieces. Tying them together in this book with

cohesive examples was a challenge.

It is my sincere hope that readers will enjoy this book and benefit from it.

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IntroduCtIon

Structure of the Book

This book contains 13 chapters: Each chapter introduces a new topic from the Java

Scripting API and the JavaScript language. Each chapter makes use of the material

covered in the previous chapters.

Chapter 1, Getting Started, introduces you to the Java Scripting API and

demonstrates how to write your first Java program to execute a script written in Nashorn.

It walks through the steps that are needed to download and install other scripting

languages such as Groovy, Jython, and JRuby. Finally, this chapter takes a brief tour of the

classes and interfaces contained in the

javax.script

package, describing their usages

and relationship with other classes.

Chapter 2, Executing Scripts, shows how to execute a script, which is stored in a file.

It also demonstrates how to pass parameters from a Java application to a scripting engine,

and vice versa.

Chapter 3, Passing Parameter to Scripts, discusses advanced techniques and all the

internal setups that are involved in passing parameters between a Java application and

a scripting engine. It starts with a detailed description of the terms binding, scope, and

script context. Later, it explains in detail with several illustrations how bindings, scope,

and script context work together in the Java Scripting API. Each explanation is paired with

a snippet of code, a complete program, or both. The chapter ends with a program that

shows how to redirect outputs from a script to a file.

Chapter 4, Writing Scripts in Nashorn, covers the JavaScript language in great detail

as described in the ECMAScript 5.1 specification that is supported by the Nashorn engine.

Chapter 5, Procedures and Compiled Scripts, explains how to invoke top-level

procedures, functions, and object-level methods written in a scripting language from a

Java application. It explains how to compile scripts in intermediate form, if supported by

the scripting engine, and execute them repeatedly.

Chapter 6, Using Java in Nashorn, explains how to use features and constructs of

the Java programming language inside scripting languages. The Java features discussed

are importing Java classes, creating Java objects, using Java overloaded methods,

implementing Java interfaces, and so on.

Chapter 7, Collections, explains untyped and typed arrays in Nashorn. It also

explains how to use Java collection classes such as

java.util.Set

and

java.util.Map

in Nashorn.

Chapter 8, Implementing a Script Engine, discusses the steps needed to implement

a new script engine. It explains all classes and interfaces in the Java Scripting API that

are involved in creating a new script engine. It walks through the deployment setup that

makes a script engine autodiscoverable by a script engine manager. In the process, it

creates a simple script engine, which we call JKScript, which is capable of executing an

arithmetic expression.

Chapter 9, The jrunscript Command-Line Shell, explains how to use the

jrunscript

command-line shell to execute script using different scripting engines.

Chapter 10, The jjs Command-Line Tool, explains how to use the

jjs

command-line

tool to execute Nashorn scripts in different modes. It walks through the syntax and the

options for the command-line tool. Several examples are provided to illustrate the usage

of the shell.

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