Migrating Projects to JDK 9: Pitfalls and Solutions
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Java 9 brings revolutionary changes. There is a big difference between their adoption and adoption of similarly revolutionary features of Java 8: lambdas and streams could gradually be included in a project, but Jigsaw requires some significant changes to the existing code. Jersey and Tyrus are popular open source libraries of considerable size and cherish backward compatibility. This session presents lessons learned during a migration to Java 9 and adoption of Jigsaw features. The nature of the projects and their features—such as resource injection or scanning and using user-provided (thus unknown, in standard dependency view) classes—make the migration particularly interesting and informative for future Java 9 adopters.
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Migrating Projects to JDK 9: Pitfalls and Solutions
- 9. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Jigsaw • Module is a base element of Jigsaw runCme • Each module can declare – Dependencies on other modules • TransiCve, staCc, syntheCc, mandated – Exported packages (!) – Used Services – Provided Services (formerly META-INF/services) • (there is no version) – (it CAN be added later by “jar” command) 9 What is a module?
- 10. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Jigsaw 10 module my.module { requires java.base; requires transitive javax.ws.rs.api; exports org.my.module.package; exports org.my.module.package to moduleName; uses org.my.module.package.InterfaceName; provides org.my.module.package.InterfaceName with org.my.module.package.ImplName; }
- 12. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Mapping – Maven module (groupId:arCfactId) to Jigsaw module name – Maven dependencies to Jigsaw “requires” – ExporCng packages – META-INF/services/* to provides X with Y; • Declaring Service interfaces • Jersey has 170+ modules… 12 Back to Jersey
- 13. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Maven module (groupId:arCfactId) to Jigsaw module name – groupId.arCfactId + (s/-/./g) • META-INF/services/* to provides X with Y; • ExporCng packages – Export all for now 13 Back to Jersey
- 14. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Maven dependencies mapping to Jigsaw “requires” – Maven dependency scopes: compile, provided, runCme, opConal, system, .. – Jigsaw requires can be: transiCve, staCc • There is no direct mapping for Mavens opConal and provided scopes • Easy way out is to map all dependencies to “transiCve”, which means “requires transiCve” – Ok for now, we’ll get back to that later 14 Back to Jersey
- 15. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Classpath – Good old classpath, modelled as the “unnamed module” – Requires everything, exports none • Modulepath – When a module (jar, exploded, ..) is on module path, it is treated as a module – When a jar without module-info.java is on module path, it is treated as an automaCc module • Exports all packages, Requires all modules on the module path (*) • Name derived from the jar name 15 Classpath vs Modulepath
- 16. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • How to build Java 9 module? – javac –target 9 –source 9 –p $CP –mp $MP $(find . -name "*.java”) • Maven support – compiler plugin version “3.6-jigsaw-SNAPSHOT” – Put dependencies on the module path instead of classpath 16 Back to Jersey --class-path <path>, -classpath <path>, -cp <path> Specify where to find user class files and annotation processors --module-path <path>, -p <path>, -modulepath <path> Specify where to find application modules
- 19. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Trivial build issues – Add “requires” for java pla@orm modules • java.logging, java.naming, java.acCvaCon, java.xml.bind, java.desktop, java.management – OSGi bundle plugin and other stuff • Exclude, it won’t work anyway • hTp://openjdk.java.net/projects/penrose/ • “The goal is to explore and implement interoperability between OSGi and Jigsaw.” – Maven shade plugin – JAXB Maven plugin • Test compilaCon (let’s skip it for now) 19 Back to Jersey
- 22. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Single package can be provided only by a single module – Having 2 modules which export same package is an error • appengine.api jar (automaCc module) includes javax.acIvaIon, which is already provided by pla@orm module java.acIvaIon – This is a no go in Jigsaw • Weld (2.2.14.Final) – [ERROR] …/module-info.java: module X reads package org.jboss.weld.context from both weld.core.impl and weld.api – SCll the same issue 22 Split package issue
- 27. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Part of Java EE API which is included in the JDK – Similarly as JAX-B, JAX-WS, Corba, TransacCons, … • Jersey depends on javax.annotaCon-api:1.2 • JDK includes version <1.2 (module java.annotaCons.common) • @Priority is @since 1.2 • java.se.ee requires java.annotaCons.common 27 Back to Jersey – javax.annotaIon – “common annotaIons”
- 28. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build • Jersey uses hk2 as DI framework • exports packageName; doesn’t guarantee access to private objects/fields – It used to .. Last week J • Maven war plugin – XStream serializaCon library 28 exports private
- 29. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | ServiceLoader • META-INF/services – uses X; // X is an interface – provides X with Y // X is an interface, Y is an implementaCon class • Jersey use slightly more complex – Internal API for looking up classes (adding implementaCons in injecCon fw binding phase) • Classes are looked up from different module -> missing uses -> cannot be declared since the iface name is not known – ReflecCon for the rescue – Class.getModule().addUses(…) 29
- 31. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Build Summary • 126 modules – CausaliCes • Bundles • All War examples • OSGi and mulCmodule tests • Let’s try to run the example! – Maven exec plugin – IDE support – …? 31
- 33. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Test • Automated tesCng • Maven compile plugin – Broken with latest jdk build • Maven surefire plugin – Doesn’t seem to be ready yet • Full manual approach since now 33
- 34. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Jlink • Tool which produces opCmized runCme for specific usecase • Packaging minimal set from JDK with the applicaCon – $ jlink --module-path $JAVA_HOME/jmods/:"$MP" --add-modules org.glassfish.jersey.examples.helloworld --output ./jlink-test – Error: module-info.class not found for javax.annotaCon.api module • Jlink requires all modules to be named modules – L 34
- 35. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Packaging • Jersey provides jax-rs-ri bundle • What’s a bundle? – Fat jar • Executable Fat Jar – L • Executable Uber Jar! – What the hell is an uber jar? 35 Bundles..
- 38. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | TODO • Use requires transiIve only where required – Only when the dependency is exposed in exported package • exports X to Y; – Export internal packages strictly to org.glassgish.jersey.* modules – Y is required to be on the module path • DistribuCon packages – Use mulC-release support in JAR files – Distribute Java 9 enabled Jersey JARs 38
- 39. Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | Most of the credits goes to… • Alex Buckley • Alan Bateman • Were to get latest Jigsaw build – hTps://jdk9.java.net/jigsaw/ 39