Tag Archives: maven

[2019 oracle code one] maven stories

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Broken Built Tools & Bad Habits: The Maven Stories

Speaker: Robert Schoite @rfschoite

For more blog posts, see The Oracle Code One table of contents


General

  • Instructions change over time and following practices from prior generations can get you in trouble.
  • Advice from Maven 1 and 2, may not apply to Maven 3
  • When learn new things – analyze, google/stack overflow, ask colleagues
  • When things fail – do three things when learning. Or can fix, create workarounds.
  • Workarounds tend to turn into a pattern
  • CI server is the neutral judge. Counter to “it works on my machine”
  • Apache tests latest Maven 3.0, 3.2, 2.3, 3.5 and 3.6 with java 7. And 3.6.1 with Java 7, 8, 11, 12 and 13 early access. Test on Ubunto and Windows

Why it works on your machine but not server

  • Changed code
  • OS – ex: Windows not case sensitive
  • JDK
  • Version of Maven
  • Files – regular files/directories
  • Properties – system/environment

Options to troubleshoot

  • -v version of Maven
  • -V version info and run build. Good for running on CI server
  • -e execution error messages
  • -X execution debug info

Local repo

  • No TTL (time-to-live)
  • Maven 2 – dumb cache
  • Maven 3: _remote.repositories – verify cached artifacts still exist
  • Designed for single user. CI server can be multi user and corrupt files due to concurrent writes/reads
  • Takarai Concurrent Local Repository – adds file locking to repo
  • Checksums not verified by default. -C is for strict checksums to fail if don’t match or -c for lax checksums to warn if don’t match. Shouldn’t be a problem now since binary repos have checksums. In Maven 4, will probably turn on by default.
  • Maven 2 and 3 share directory. In future, might separate SNAPSHOTS or by different remote repos

Multi modules

  • In Maven 2, not aware of reactor. Dependencies had to exist in local repo
  • Maven 3 is reactor aware so shouldn’t need install anymore. [for this scenario]
  • Can use installAtEnd/deployAtEnd experimental feature to wait until the last module runs

Flow

  • Locally run mvn verify
  • On CI Server, run mvn deploy. (hard to write without install so that is fine too)
  • This technique means all SNAPSHOTS are served by repo manager

Performance

  • Aim for clean Maaven output
  • Don’t write to System out/error
  • Don’t log during testing loglevel = off
  • Can set Maven flag to quiet if needed

Files

  • Replacing files is a waste
  • Most plugins can handle incremental execution
  • Avoid maven clean because forced rework
  • He wrote a plugin to nag you about using clean and install

Properties

  • Don’t change version of Java or a dependency on the command line

Versions

  • Maven 3.5.0 comes with CI friendly placeholders. Can specify revision, sha1 or changelist in version #. Ex 3.1.0-JIRA101-SNAPSHOT
  • Need relative path or GAV when building. Dependencies must use GAV
  • Maven 3.7 will probably require Java 8+

My take

This was good. Assuming you are familiar with Maven, there was a lot of info covered quickly but not hard to understand. If you don’t know Maven, I suspect this would have gone over your head. I learned a few new things so I’m happy.

JavaOne – Maven BOF

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“Maven 5 BOF”

Speaker: Brian Fox, Manfred Moser & Robert Scholte

For more blog posts from JavaOne, see the table of contents

[I was late because we talked more about JUnit 5 after the BOF]

Only 26.4% of Maven Central traffic is from Maven. Nothing else is more than 10% though; not even Ivy or Gradle

Some projects don’t have snapshots; instead every commit is a release

Talked about version ranges. Depends on proximity to your project rather than the latest version. Important to clean up pom dependencies before Java 9 so not in module path. Use Maven dependency plugin (analyze) to find unused ones. Make sure to use latest version of depedency plugin.

Maven won’t generate module descriptor. Different purpose. Not all modules are dependencies. More info in module descriptor. What to export is a decision that needs to be decided by developer. jdeps can generate a rough descriptor to get started based on binaries.

Can have .mvn file inside projects with preferences startig in Maven 3.3.5. For example, you can specify to provide more memory.

Shouldn’t be issues going from 3.3.5 to 3.5.9

Maven (dependency) resolver is now a standalone project

JavaOne – Project Jigsaw – Integration with Tools

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“Project Jigsaw – Integration with Tools”

Speaker: Alexandru Jecan (author of Java 9 Modularity Revealed)

For more blog posts from JavaOne, see the table of contents

What expect build tools and IDEs to do

  • Code completion (IDEs only)
  • Make things easier
  • Work with class path and module path

Maven

  • Only Maven 3+ supports Java 9.
  • No changes to Maven core to run on Java 9
  • presence of module-info.java decides if Maven uses module path
  • Need Maven compiler plugin 3.6.1 to compile Java 9 code
  • Discourages using automatic module name
  • GAV not related to module name. Continue to use GAV.
  • Use module name in module-info.java – double work
  • Maven does not generate “requires” clauses for module-info.java
  • Can add <compilerArgs> options for -add-modules or -add-exports
  • New tag <release> which takes precedence over source/target tags. Recomended compiling twice or backward compatbility. once for java 9 modules and once for java 8. [why? isn’t that what multi release ars are for?]
  • maven-exec-plugin – can configure module path
  • taked abut updating maven toolchain file [not clear how this differs than prior versions of java]
  • maven-jdeps-plugin – can automatically generate module descriptor [but said earlier couldn’t]
  • maven-jmod-plugin – new plugin; not yet released. Creates and lists content of jmod files. Merge native code into jar
  • maven-jlink-plugin – new plugin; not yet released. Creates runtime images
  • maven-depdendency-plugin – said lists GAV [not clear how changed

Gradle
No first class support for Java 9 yet. Coming soon. [but said using; puzled?]

Ant
Ant 1.9.8+ support JDK 9 modules for java/javac/junit. [yet Ant doesn’t support JUnit 5]

Loom

  • New build tool for Java 9
  • Uses YAML config. Uses Maaven repo.
  • Supports JUnit 5,

loom.builders

Moditect
Maven plugin that generates module-info.java based on dependencies. Says helps a little but doesn’t do all the work. [how?]

SonarJava
SonarJava 4.11+ recognizes module keywords

Graphviz
Open source visualization software
Reads jdeps input to generate graphical representation of Jigsaw. As can IDES

IDEs

  • NetBeans, Eclipse and IntelliJ all understand modules clauses [if you count pre-release versions]
  • Also offer autocompletion, syntax higlighting, etc
  • NetBeans 9 – not yet released; must build yourself. Showed editing module path, visual of module dependencies, jshell, jlink
  • Eclipse Oxygen with Java 9 support – came out 9/27/17. Ten second demo
  • IntelliJ 2017.1+ – Mark directory as source root so directory name matches module name. Errors on common module errors, Showed module editing, module dependencies and other features

Open source readiness

How to modularize your app

  • Introduce modue-info.java by creating manually or running jdeps to generate
  • Problems: using JDK internal APIs (ignore warning or fix), using odule not availalbe such as xml bindings (add-modules at compile and runtime), cyclic dependencies (can have at runtime but not compile time), split packages (Oracle plans to make change in later version of Java to deal with this)

    • [Note: He recommended renaming packags as a solution to spit packages. That sounds like a horrible idea unless you can guarantee only you call that code]

    My take before session: You know how they say that first impressions matter? The speaker is wearing a suit. 90% of the people in the room are wearing jeans. Two people in the room are wearing a suit The speaker and someone he knows. Then he showed the table of contents. There are 29 points in 45 minutes in the outline. Preparing to have my head spin!

    My take after session: He is in fact technical. The suit was misleading! The pace was way too fast though; drinking from a fire hose. Not enough time to understand/process many of the points. He talks fast (as do I), but key is to *pause* if you talk fast so people can catch up. Also the side transitions were distracting. A cube transition is cute. But if you are reading when it moves, it is disorienting. And due to the speed, there was a good chance of being reading when transitions started. This was good information, but should have been two sessions so split up and a decent pace. And omiting how to migrate your libraries; that’s a talk on its own There is a Maven BOF tonight; maybe folks can discuss more then!

    One minute after the official end time, he asked if there were questions. My head was spinning with questions. [I didn’t even have time to process which was most important]. Another attendee asked if having JUnit tests in a parallel directory with the same package name is a split package. The speaker said yes and went on to say to wait for Java 10 or rename. I interjected at that point. Unless you are distributing a test jar, I don’t think this is a problem. In fact, most IDEs compile both the /src/main/java and /test/main/java directories to the same folder. I stated this and asked the speaker if he agreed. He said yes.