Java is evolving rapidly: Maven helps you staying on track Hervé Boutemy - @hboutemy Arnaud Héritier - @aheritier CORINTHIA ¡HOTEL BUDAPEST, ¡HUNGARY – OCTOBER ¡1-‑2, ¡2015 ¡–
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, Support ¡Engineer • 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
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?
8 7 6 We’ll learn you how to juggle Java is 20 years old Juggle with different Java versions (JDKs, JREs) Version First ¡publication JDK ¡Alpha ¡and ¡Beta 1995 JDK ¡1.0 January, ¡1996 To be able to use new JDK ¡1.1 February, ¡1997 features from recent tools J2SE ¡1.2 ¡(playground) December, ¡1998 J2SE ¡1.3 ¡(kestrel) May, ¡2000 J2SE ¡1.4 ¡(merlin) February, ¡2002 And ensure compatibility J2SE ¡5.0 ¡(tiger) September, ¡ 2004 against production target Java ¡SE ¡6 ¡(mustang) December, ¡ 2006 Java ¡SE ¡7 ¡(dolphin) July, ¡ 2011 Java ¡SE ¡8 March, ¡ 2014 Java ¡SE ¡9 Early ¡ 2016
Java and you • Who is mainly using – In production? – Version 9 to develop? – In production? – Version 8 to develop? – In production? – Version 7 to develop? – In production? – Version 6 to develop? – In production? – Version <6 to develop?
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 version during 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.html http://www.ibm.com/developerworks/java/jdk/lifecycle/ http://maven.apache.org/docs/history.html
Bytecode Version
Bytecode Version Java ¡8 ¡ ¡ ¡ ¡= ¡52 ¡(0x34) Java ¡7 ¡ ¡ ¡ ¡= ¡51 ¡(0x33) Java ¡6 ¡ ¡ ¡ ¡= ¡50 ¡(0x32) .class ¡file ¡format Java ¡5 ¡ ¡ ¡ ¡= ¡49 ¡(0x31) Java ¡1.4 ¡= ¡48 ¡(0x30) • 4 ¡bytes: ¡magic ¡number Java ¡1.3 ¡= ¡47 ¡(0x2F) • 2 ¡bytes: ¡minor ¡version Java ¡1.2 ¡= ¡46 ¡(0x2E) • 2 ¡bytes: ¡major ¡version Java ¡1.1 ¡= ¡45 ¡(0x2D) • Binary backward compatibility – JVM can execute old bytecode – but not newer bytecode, or… • java.lang.UnsupportedClassVersionError
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 7 How? – 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 choose with build tools requirements in mind JDK used JRE used JRE to in build by execute tasks Maven & the (javac…) plugins application Must ¡swap ¡constraints: ¡application ¡over ¡build
Maven Toolchains: The ultimate weapon • Allows to use a JDK to run “build” steps (compilation, tests execution, …) different from the JRE used to 8 7 launch Maven and its plugins 6 – You can use a recent JRE for Maven and its plugins – For each application, Maven uses the JDK version required by your project JDK used JRE to JRE used in build execute by tasks the Maven & (javac…) application plugins Allows ¡to ¡easily ¡jungle ¡between ¡various ¡JDKs ¡to ¡ensure ¡there ¡is ¡no ¡ risk ¡for ¡the ¡targeted ¡application
Demo
Maven Toolchains • Available since Maven 2.0.9 (2008/04) 1. Available tools are configured (path….) in the file ~/.m2/toolchains.xml 2. 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 evolutions going faster (Yeahhh) the need to mixup different versions of Java will be a 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 ● + 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
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