Java 9 Revealed. For Early Adoption and Migration. Kishori Sharan

Transcription

1 Java 9 Revealed For Early Adoption and Migration Kishori Sharan

2 Java 9 Revealed: For Early Adoption and Migration Kishori Sharan Montgomery, Alabama, USA ISBN-13 (pbk): ISBN-13 (electronic): Library of Congress Control Number: Copyright Kishori Sharan 2017, corrected publication 2018 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. Trademarked names, logos, and images may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, logo, or image we use the names, logos, and images only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Managing Director, Apress Media LLC: Welmoed Spahr Acquisitions Editor: Steve Anglin Development Editor: Matthew Moodie Coordinating Editor: Mark Powers Cover designed by estudiocalamar Cover image designed by Freepik ( Distributed to the book trade worldwide by Springer Science+Business Media New York, 233 Spring Street, 6th Floor, New York, NY Phone SPRINGER, fax (201) , orders-ny@springer-sbm.com, or visit Apress Media, LLC is a California LLC and the sole member (owner) is Springer Science + Business Media Finance Inc (SSBM Finance Inc). SSBM Finance Inc is a Delaware corporation. For information on translations, please rights@apress.com, or visit rights-permissions. Apress titles may be purchased in bulk for academic, corporate, or promotional use. ebook versions and licenses are also available for most titles. For more information, reference our Print and ebook Bulk Sales web page at Any source code or other supplementary material referenced by the author in this book is available to readers on GitHub via the book's product page, located at For more detailed information, please visit Printed on acid-free paper

3 To my friend Richard Castillo, who has been incredible in helping me in my journey of writing books. Without his help, I could not have published my three-book Harnessing Java 7 series. Thank you, my friend, for all your help.

4 Contents About the Author...xvii About the Technical Reviewer...xix Acknowledgments...xxi Introduction...xxiii Chapter 1: Introduction... 1 Introduction to JDK How to Read This Book... 2 System Requirements... 3 Installing the NetBeans IDE... 4 Downloading the Source Code... 5 Chapter 2: The Module System... 7 Life Before Java The New Module System... 9 What Is a Module? Module Dependencies Module Graph Aggregator Modules Declaring Modules Module Names Controlling Access to Modules Declaring Dependency Configuring Services v

5 Module Descriptors Compiling Module Declarations Module Version Module Source Files Structure Packaging Modules A Module in a Directory A Module in a Modular JAR A Module in a JMOD File...25 Module Path Observable Modules Summary Chapter 3: Creating Your First Module Using the Command Prompt Setting Up the Directories Writing the Source Code Compiling the Source Code Packaging the Module Code Running the Program Using the NetBeans IDE Configuring the IDE Creating the Java Project Setting the Project Properties Adding the Module Declaration Viewing Module Graph Writing the Source Code Compiling the Source Code Packaging the Module Code Running the Program Summary vi

6 Chapter 4: Module Dependency Declaring Module Dependency Troubleshooting the Example Empty Package Error Module Not Found Error...66 Package Does Not Exist Error Module Resolution Exception Implicit Readability Qualified Exports Optional Dependency Accessing Modules Using Reflection Open Modules Opening Packages Using Deep Reflection Type Accessibility Splitting Packages Across Modules Restrictions in Module Declarations Types of Modules Normal Modules Open Modules Automatic Modules Unnamed Modules Migration Path to JDK Disassembling Module Definitions Summary Chapter 5: Implementing Services What Is a Service? Discovering Services vii

7 Providing Service Implementations Defining the Service Interface Defining Service Providers Defining a Generic Prime Service Provider Defining a Faster Prime Service Provider Defining a Fastest Prime Service Provider Testing the Prime Service Selecting and Filtering Providers Testing Prime Service in Legacy Mode Summary Chapter 6: Packaging Modules The JAR Format What Is a Multi-Release JAR? Creating Multi-Release JARs Rules for Multi-Release JARs Multi-Release JARs and JAR URL Multi-Release Manifest Attribute The JMOD Format Using the jmod Tool Summary Chapter 7: Creating Custom Runtime Images What Is a Custom Runtime Image? Creating Custom Runtime Images Binding Services Using Plugins with the jlink Tool The jimage Tool Summary viii

8 Chapter 8: Breaking Changes in JDK The New JDK Versioning Scheme Version Number Prerelease Information Build Information Additional Information Parsing Old and New Version Strings Version Changes to System Properties Using the Runtime.Version Class Changes to the JDK and JRE Layout Changes in JDK and JRE Behavioral Changes Changes in Class Loaders Accessing Resources Accessing Resources Before JDK Accessing Resources in JDK Using JDK Internal APIs Patching Module Contents Summary Chapter 9: Breaking Module Encapsulation What Is Breaking Module Encapsulation? Command-Line Options The --add-exports Option The --add-opens Option The --add-reads Option The --illegal-access Option An Example Using Manifest Attributes of a JAR Summary ix

9 Chapter 10: The Module API What Is the Module API? Representing Modules Describing Modules Representing Module Statements Representing a Module Version Other Properties of Modules Knowing Module Basic Info Querying Modules Updating Modules Accessing Module Resources Annotation on Modules Loading Classes Working with Module Layers Finding Modules Reading Module Contents Creating Configurations Creating Module Layers Summary Chapter 11: The Java Shell What Is the Java Shell? The JShell Architecture Starting the JShell Tool Exiting the JShell Tool What Are Snippets and Commands? Evaluating Expressions Listing Snippets Editing Snippets Rerunning Previous Snippets x

10 Declaring Variables Import Statements Method Declarations Type Declarations Setting Execution Environment No Checked Exceptions Auto-Completion Snippets and Commands History Reading JShell Stack Trace Reusing JShell Sessions Resetting the JShell State Reloading the JShell State Configuring JShell Setting the Snippet Editor Setting Feedback Mode Creating Custom feedback Modes Setting Up Startup Snippets Using JShell Documentation The JShell API Creating a JShell Working with Snippets Handling Snippet Events An Example Summary Chapter 12: Process API Updates What Is the Process API? The Current Process Querying Process State Comparing Processes xi

11 xii Creating a Process Obtaining a Process Handle Terminating Processes Managing Process Permissions Summary Chapter 13: Collection API Updates The Background Unmodifiable Lists Unmodifiable Sets Unmodifiable Maps Summary Chapter 14: The HTTP/2 Client API What Is the HTTP/2 Client API? Setting Up Examples Creating HTTP Clients Processing HTTP Requests Obtaining an HTTP Request Builder Setting HTTP Request Parameters Setting the Request Redirection Policy Using the WebSocket Protocol Creating a Server Endpoint Creating a Client Endpoint Running the WebSocket Program Troubleshooting the WebSocket Application Summary Chapter 15: Enhanced Deprecation What Is Deprecation? How to Deprecate an API Updates in JDK

12 Suppressing Deprecation Warnings A Deprecated API Example Static Analysis of Deprecated APIs Dynamic Analysis of Deprecated APIs No Deprecation Warnings on Imports Summary Chapter 16: Stack Walking What Is a Stack? What Is Stack Walking? Stack Walking in JDK Drawbacks to Stack Walking Stack Walking in JDK Specifying Stack-Walking Options Representing a Stack Frame Obtaining a StackWalker Walking the Stack Knowing the Caller s Class Stack-Walking Permissions Summary Chapter 17: Reactive Streams What Is a Stream? What Is Reactive Streams? The Reactive Streams API in JDK Publisher-Subscriber Interactions Creating Publishers Publishing Items A Quick Example Creating Subscribers Using Processors Summary xiii

13 Chapter 18: Streams API Updates New Stream Operations New Collectors Summary Chapter 19: Platform and JVM Logging Platform Logging API Setting up Log4j Libraries Setting Up a NetBeans Project Defining a Module Adding a Log4j Configuration File Creating a System Logger Creating a Logger Finder Testing the Platform Logger Unified JVM Logging Message Tags Message Levels Message Decorations Message Output Destination The -Xlog Syntax Summary Chapter 20: Other Changes in JDK The Underscore Is a Keyword Improved try-with-resources Blocks Diamond Operator in Anonymous Classes Private Methods in Interfaces... on Private Methods Discarding Process Outputs New Methods in the StrictMath Class Changes to the ClassLoader Class xiv

14 New Methods in the Optional<T> Class Additions to the CompletableFuture<T> Class Spin-Wait Hints Enhancements to the Time API The Clock Class The Duration Class The ofinstant() Factory Method Obtaining Epoch Seconds Stream of LocalDate New Formatting Options Stream Operations with Scanner Enhancement to the Matcher Class Enhancement to the Objects Class Comparing Arrays The Applet API Is Deprecated Javadoc Enhancements Native Desktop Features Object Deserialization Filters Additions to Java I/O API Summary Erratum... E1 Index xv

15 About the Author Kishori Sharan works as a senior software engineer lead at IndraSoft, Inc. He earned a master s of science degree in computer information systems from Troy State University, Alabama. He is a Sun-certified Java 2 programmer and has over 20 years of experience in developing enterprise applications and providing training to professional developers using the Java platform. xvii

16 About the Technical Reviewer Manuel Jordan Elera is an autodidactic developer and researcher who enjoys learning new technologies for his own experiments and creating new integrations. Manuel won the 2010 Springy Award Community Champion and Spring Champion In his little free time, he reads the Bible and composes music on his guitar. Manuel is known as dr_pompeii. He has tech reviewed numerous books for Apress, including Pro Spring, 4th Edition (2014), Practical Spring LDAP (2013), Pro JPA 2, Second Edition (2013), and Pro Spring Security (2013). Read his 13 detailed tutorials about many Spring technologies and contact him through his blog at blogspot.com. You can also follow him on xix

17 Acknowledgments My wife Ellen was patient when I spent long hours at my computer working on this book. I want to thank her for all of her support in writing this book. I want to thank my family members and friends for their encouragement and support: my mom Pratima Devi; my elder brothers, Janki Sharan and Dr. Sita Sharan; my nephews, Gaurav and Saurav; my sister Ratna; my friends, Karthikeya Venkatesan, Preethi Vasudev, Rahul Nagpal, Ravi Datla; and many more friends not mentioned here. I would like to thank my coworkers, Forrest Corky Butts, Antonio Mathews, and Yolanda Robinson, for their support. My sincere thanks are due to the wonderful team at Apress for their support during the publication of this book. Thanks to Mark Powers, the Editorial Operations Manager, for providing excellent support and for being exceptionally patient with me when I was slow in producing manuscript. My special thanks to Manuel Jordan Elera, the technical reviewer, whose thorough approach reviewing the book helped weed out many technical errors. Last but not least, my sincere thanks to Steve Anglin, the Lead Editor at Apress, for taking the initiative for the publication of this book. The original version of chapters 2, 4, 9, 11, 12 and 14 was revised. An erratum to all these chapters can be found at xxi

18 Introduction How This Book Came About The Java community is excited to see the module system and Java shell finally added to the Java platform in JDK 9, and so am I. After all, we had to wait over 10 years to see this module system in action. Several previous JDK releases saw prototypes of the module system, which were later dropped. The introduction of the module system in JDK 9 has also been a bumpy ride. It went through several iterations of proposals and prototypes. I started writing this book in early I have to admit that this was a difficult book to write. I had to race against the JDK release date and the changes the Java team was making to the module system. I would write about a topic to find a few months later that the final release date for JDK 9 had moved and whatever I had written was no longer valid. Today is the last day of February 2016 and it seems that the dust has finally settled the Java team and the Java community are happy with the module system and you are going to get this book as it exists today. JDK 9 is scheduled to be released in late July JDK 9 is feature complete at the time of this writing. It is very unlikely that you will see many instances where something covered in this book does not work. However, five months is a long time in terms of software releases, so don t be surprised if a piece of code does not work and you have to tweak it a bit to make it work when you read this book. In the beginning, this book was supposed to be 140 pages. As my writing progressed, I thought it would be a disservice to readers to write a book so short covering one of the biggest additions to the Java platform. I thank my publisher who never complained about me adding hundreds of pages to the book. I devoted nine chapters (Chapter 2 to Chapter 10) solely to describing the new module system. Chapter 11 covers the Java shell (JShell) with unmatched details. I spent countless hours researching this topic. I was writing on topics that were under development. There were no materials on the Internet or in books that I could find to learn about these topics. One of the biggest challenges was the fast-changing JDK implementation during the development phase. My main sources of research were the Java source code, Java Enhancement Processes (JEPs), and Java Specification Requests (JSRs). I also spent quite a bit of time reading the Java source code to learn more about some of the new topics in JDK 9. It was always fun to play with Java programs, sometimes for hours, and then add them to the book. Sometimes, it was frustrating to see that the code worked a week ago and then did not work anymore. Subscribing to the mailing lists for all JDK 9 projects helped me to stay in sync with the JDK development team. A few times I had to go through all the bugs on a JDK topic to verify that there was a bug that had not been fixed yet. All s well that ends well. Finally, I am happy that I was able to include everything that matters to readers interested in learning Java SE 9. I hope you enjoy reading the book and benefit from it. xxiii

19 Introduction The Structure of the Book This book contains 20 chapters. Chapter 1 is an introduction to JDK 9 and how to work with the book and its source code. Chapters 2 through 10 cover the module system. These chapters are designed to be read sequentially. Chapter 11 covers the Java Shell (JShell) in detail. For the most part, you can read Chapter 11 without reading the first 10 chapters. However, I recommend you read them sequentially for a complete understanding. You can read Chapters 12 through Chapter 20 in any order. They cover independent topics. The last chapter is a catch-all chapter. If a topic was small enough not to require a chapter of its own, I stuffed it into this final chapter. The Audience This book is designed for experienced Java developers who are familiar with Java SE 8. Parts of the book use Streams API, Time API, and Lambdas introduced in Java SE 8. If you know Java SE 7 or earlier versions, you can certainly benefit reading Chapters 1 through 11 of this book. These chapters teach you the module system and the Java shell. Readers are advised to use the API documentation for the Java programming language as much as possible while using this book. The Java API documentation is where you will find a complete list of everything available in the Java class library. You can download (or view) the Java API documentation from Oracle s official web site at While you read this book, you need to practice writing Java programs yourself. You can also practice by tweaking the programs provided in the book. It does not help much in your learning process if you just read this book and do not practice writing your own programs. Remember that practice makes perfect, which is also true in learning how to program using JDK 9. Source Code and Errata Source code and errata for this book can be accessed via Questions and Comments Please direct all your questions and comments to the author at ksharan@jdojo.com. xxiv