CORINTHIA  HOTELBUDAPEST,  HUNGARY– OCTOBER  1-­‐2,  2015  –

Java is evolving rapidly: Maven helps you staying on track

Hervé Boutemy - @hboutemyArnaud Héritier - @aheritier

Goal

With Apache Maven, learn how to manage Java evolutions quietly

Menu

• Appetizer– Java duke and maven owl cocktail

• Starter– Bytecode soup with its enforcer zest

• Main dish– A piece of Animal Sniffer and its accompaniments

• Dessert– The toolchain and its diligence of JDKs

Who are we?

Hervé Boutemy

• Maven Committer since 2007,• Maven PMC Member since 2009, • Apache Foundation Member since 2011, • Maven PMC Chair since July 2014, • Gave a hand on practically every Apache

Maven code, but more in depth on...• Encoding, Maven Ant Tasks, Modello, maven-site-plugin,

Doxia,• Archetype, Plugin Tools,• maven-checkstyle-plugin,Toolchains, …

Arnaud Héritier

• Maven Committer since 2004, • Maven PMC Member since 2005, • Apache Foundation Member since 2011, • I’m trying to not touch to the code... – But I’m talking a lot about Apache Maven !

http://git.io/jEFs

Support  Engineer

What is it about?

Apache Maven and you

• Who is using Maven?• Which version in general?– 3.3? – 3.2? – 3.1?– 3.0? – < 3.0?

We’ll learn you how to juggle

Juggle with different Java versions (JDKs, JREs)

To be able to use new features from recent tools

And ensure compatibilityagainst production target

Java is 20 years oldVersion First  publicationJDK  Alpha  and  Beta 1995JDK  1.0 January,  1996JDK  1.1 February,  1997J2SE  1.2  (playground) December,  1998J2SE  1.3  (kestrel) May,  2000J2SE  1.4  (merlin) February,  2002J2SE  5.0  (tiger) September,   2004Java  SE  6  (mustang) December,  2006Java  SE  7  (dolphin) July,  2011Java  SE  8 March,  2014Java  SE  9 Early  2016

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Java and you

• Who is mainly using– Version 9 to develop? – Version 8 to develop? – Version 7 to develop? – Version 6 to develop? – Version <6 to develop?

– In production?– In production?– In production?– In production?– In production?

Java and you

• Who is using many Java versions on his development workstation and switch on a regular basis?

• Who is using a different Java versionduring development and production?

The JDK choice dilemma

• Developer temptation: recent build tools, with more features, requiring recent JDK

• Manager requirement: ensure compatibility with target environment: often quite old JRE (and the same on whole landscape?)

• Miscellaneous strategies:– Conservatory: JDK = min( JRE<every apps> ) + old associated

tools…– Courageous: for each app, switch JDK & associated tools– Player (unaware?): recent JDK– Serious: recent JDK + CI and deep tests, with good coverage– Smart: Maven + a few configurations

Java & Apache Maven Roadmaps: 2009

Java & Apache Maven Roadmaps: 2009 …a little bit later…

Java & Apache Maven Roadmaps: early 2014

Java & Apache Maven Roadmaps: nowadays

Sources :http://www.oracle.com/technetwork/java/eol-­‐135779.htmlhttp://www.ibm.com/developerworks/java/jdk/lifecycle/http://maven.apache.org/docs/history.html

Bytecode Version

Bytecode Version

• Binary backward compatibility– JVM can execute old bytecode– but not newer bytecode, or…

• java.lang.UnsupportedClassVersionError

Java  8        =  52  (0x34)Java  7        =  51  (0x33)Java  6        =  50  (0x32)Java  5        =  49  (0x31)Java  1.4  =  48  (0x30)Java  1.3  =  47  (0x2F)Java  1.2  =  46  (0x2E)Java  1.1  =  45  (0x2D)

.class  file  format• 4  bytes:  magic  number• 2  bytes:  minor  version• 2  bytes:  major  version

Demo

javac & bytecode version

Javac– Default: bytecode version = JDK version– -target defines bytecode version

Maven & bytecode version

• Maven allows to easily control the version of the bytecode used in the project build– By default:

• maven-compiler-plugin sets –target 1.5• independent from JDK used

– maven-compiler-plugin’s target parameter• plugin or pluginManagement configuration• more compact: maven.compiler.target property

Maven & bytecode version

• Maven allows also to verify the version of the bytecode used in project dependencies– enforceBytecodeVersion rule from maven-enforcer-plugin

Animal Sniffer

Demo

Animal Sniffer – why?

• To check the classes and method signatures that your compiled code uses and verify that you have use only those classes and signatures available in the API you are targeting.

Even  if  its  main  known  usage  is  to  verify  the  compatibility  with  JDK  APIs,  Animal  Sniffer  is  generic and  can  be  used  to  verify  any  API  after  having  generated  its  signatures.

Animal Sniffer

Example– Using a JDK 8 to compile your code must use only APIs from

Java 7How?– Provided as 3 tools: a Maven plugin, an enforcer rule, an Ant

task.– Must be executed on compiled classes.

Limitation– Can verify only APIs signatures.– Doesn’t cover semantic

• when an exception is thrown, …– Detects the issue but doesn’t allow to fix it.

Toolchains & JDK

Maven Toolchains: The problem

• Nowadays JDK is chosen with build tools requirements in mind

Must  swap  JDK  choice  priorities:  application  over  build

JRE used by

Maven & plugins

JRE to execute

the application

JDK used in build tasks

(javac…)

Maven Toolchains: The ultimate weapon

• Allows to use a JDK to run “build” steps (compilation, tests execution, …) different from the JRE used to launch Maven and its plugins– You can use a recent JRE for Maven and its plugins– For each application, Maven uses the JDK version required

by your project

Allows  to  easily  jungle  between  various  JDKs  to  ensure  there  is  no  risk  for  the  targeted  application

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JRE used by

Maven & plugins

JRE to execute

the application

JDK used in build tasks

(javac…)

Demo

Maven Toolchains

• Available since Maven 2.0.9 (2008/04)1. Available tools are configured (path….) in the file

~/.m2/toolchains.xml2. pom.xml configures the maven-toolchains-

plugin to select the required tool with possibly some constraints (version,…)

3. “toolchain aware” plugins will automatically use the selected tool

• Tools are configured to match the current environment and are homogeneous across plugins

Maven Toolchains & JDK

• Toolchains is generic: can be used to manage any type of tool

• <type>jdk</type> toolchain is directly integrated in Maven

• “jdk-toolchain aware” plugins – m-compiler-p, m-javadoc-p, m-surefire-p, m-webstart-p, m-jarsigner-p,

exec-maven-plugin, keytool-maven-plugin, …

• Others toolchains are already existing– protobuf, netbeans, …

Toolchains recent news

• maven-toolchains-plugin 1.1 (2014/11)– More readable execution logs– Documentation to write new custom types

• Maven 3.3 (2015/3)– ${maven.home}/conf/toolchains.xml– A plugin can use another tool than the one

selected by the maven-toolchains-plugin• maven-jdeps-plugin (in progress)– uses jdeps from recent JDKs (JDK 8 or 9)

Summary

Summary

• With Java evolution going faster (Yeahhh) the need to mixup different versions of Java will be more important and will increase the risk of incompatibilities

• With Maven you are ready to– Automatically verify the compatibility by using

Animal Sniffer and the Enforcer– Use the right JDK targeted by your application

by configuring the Toolchains

Demo - Bonus● When JDK8 compiler optimizations are creating a

backward incompatibility

● New solution: JDK 9 javac -release option

● maven-jdeps-plugin

Resources

• Animal Sniffer– http://mojohaus.org/animal-sniffer/

• Enforcer plugin– https://maven.apache.org/enforcer/maven-

enforcer-plugin/• Toolchains– https://maven.apache.org/guides/mini/guide-

using-toolchains.html• Demos– https://github.com/MavenDemo/java-evolving-en

Q & A