Post on 28-Jun-2020
JVM Survival Guide Hadi Hariri
This talk
❖ For What
❖ For Who
20 years of Java
❖ The Sun and The Oracle
❖ Java The Language
❖ Java The Virtual Machine
❖ Java The Ecosystem
The Community
❖ Community Driven
❖ Not Vendor-Driven
❖ Large and Open Ecosystem
It’s an Open Platform
❖ Languages
❖ Java, Clojure, Scala, Kotlin, Frege, Groovy, JRuby, Ceylon
❖ Frameworks
❖ JavaEE, Spring, Spark, Play Framework
What to Install
Java SE
Java FX
Java EE
Java ME
JDK
JRE
Versioning
❖ Language - 1.X where X is the version
❖ Java XY - X where X is the version
❖ Usually aligned major versioning in Language and VM
Installing Java
❖ Oracle Web Site (includes Ask Toolbar)
❖ Package Managers
❖ Brew, Chocolatey
JAVA_HOME
❖ Defines where Java Virtual Machine is located
❖ On Linux/OSX if undefined
export JAVA_HOME=$(/usr/libexec/java_home)
A First Java App
Create a Java AppUse javac to compile itUse java to run itExample - firstApp
Decompiling
Decompiling exampleshow byte code and also decompiling
Multiple Classes and Files
usingClass example
Java ARchives
❖ Archive classes files into single jar file
❖ Provide metadata with METAINF file
❖ jar command line to create jar files
❖ war is the web equivalent of jar
Creating Jar Files
createJar.sh samples
Conventions
❖ In Java
❖ Virtual by default
❖ Open by default
❖ In other languages
❖ It depends
Conventions
❖ Packages and Modules
❖ Accessibility and Visibility Modifiers
❖ In Java, single class per file is enforced
Conventions
❖ Java and Java-inspired languages
lowerCamelCaseNotation
Namespaces
❖ Or death by a hundred folders
ext.vendor.module.subsystem
❖ Individual imports has been widely adopted
Namespaces
namespaces demo
The Class Path
❖ Defines where Java Classes are located
❖ Set via command line java -cp
❖ Most common reason for NoClassDefFoundError
Class Loaders
❖ Responsible for loading classes
❖ Each class loader has a parent
❖ Delegates what it can to its parent
Class Loaders
Parent
Bootstrap Class Loader
Load java.lang and other key classes
Parent
ExtensionClass Loader
Load java.ext.dirs
Parent
SystemClass Loader
Load classpath
Other Common Errors
❖ NoSuchMethodError - wrong version of class loaded
❖ ClassCastException - casting to wrong type
❖ IllegalAccessError - wrong access modifier
Using ClassPath
usingClass Path example Compile and remove to show exception
Loading Classes
loadingClasses Example
Build Systems
❖ Ant
❖ IntelliJ IDEA
❖ Eclipse
Build and Dependency Management
❖ Maven
❖ Gradle
Maven
❖ XML-Based
❖ Extensible
❖ Supports templates
❖ Maven Central Repository for Packages (and custom)
Maven
mavenSamplemavenDependencymavenZipmavenTeamCity
Gradle
❖ Not XML a.k.a. a better DSL
❖ Based on Groovy
❖ Extensible
❖ Somewhat template support (gradle --init)
❖ Maven Central Repository for Packages (and custom)
Gradle
gradleSamplesampleApp - app plugin
Working with Resources
❖ Resource folder to ship contents along with your app
❖ Ability to define in Maven/Gradle
Resources
resourcesSampleresourcesSampleMaven
Garbage Collection
❖ Generational (Young, Old, Permanent)
❖ The “IDisposable” is Closeable
❖ The “using” is “try-with-resources”
Asynchronous Programming
❖ CompletableFuture
❖ RxJava and adapters
Generics
❖ Most languages support Generics
❖ Reified Generics on JVM
Genericsexample of genericsexample of call site and covarianceexample of reflection
Testing Frameworks
❖ JUnit - The Standard
❖ TestNg
❖ Spek
Testing
junitjunit from Java and Kotlinspek
JavaEE
❖ The Dreaded Java 2 EE Glorious Enterprise
❖ Application Servers
Web Frameworks
❖ Servlets and Application Containers
❖ Jetty, TomCat
Spring
Spring
❖ Application Framework
❖ Web, Security, Templating, SQL, AWS, Social
❖ start.spring.io as generator
Vert.x
Vert.x
vertx example
Other Interesting Libraries
❖ Mockito for mocking
❖ GSon and Jackson for JSON Serialisation
❖ JodaTime for Calendar and Time Management
❖ Netty a low-level network client and server library
Summary
❖ Java is a very vibrant ecosystem
❖ Many languages, many frameworks
❖ There is no single vendor driven strategy as such