Add basic Github workflow for CI (initially for Java 8, 11)

[garretwilson]

I'm trying to build a fork of the master branch of ClassMate using OpenJDK 17 on Windows and Maven 3.9.4. I do a simple:

mvn verify

I get:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project classmate: Compilation failure: Compilation failure:
[ERROR] Source option 6 is no longer supported. Use 7 or later.
[ERROR] Target option 6 is no longer supported. Use 7 or later.

As v3.8.1 is a pretty old version of the Maven compiler plugin (probably inherited from com.fasterxml:oss-parent:43), I would guess that the issue here is my Java 17; it probably doesn't support Java 6—which was released almost 20 years ago!

Just for "fun" I switched to Java 7:

<version.jdk>7</version.jdk>

This gives me all sorts of new errors:

[ERROR] Failures: 
[ERROR]   TestMemberResolver.testAddOverridesFromInterfaces:292 expected:<4> but was:<6>
[ERROR]   TestTypeDescriptions.testSimpleTypes:38 expected:<...va.lang.CharSequence[]> but was:<...va.lang.CharSequence[,java.lang.constant.Constable,java.lang.constant.ConstantDesc]>
[ERROR]   ResolvedObjectTypeTest.testGetStaticFields:81 Expected 3 (JDK 1.6), 4 (1.7/1.8) or 6 (1.9) static fields, got 7; fields: [serialVersionUID, COMPACT_STRINGS, serialPersistentFields, REPL, CASE_INSENSITIVE_ORDER, LATIN1, UTF16]

I'm guessing these are unit tests that fail under Java 7 for whatever reason (assuming they weren't failing for you already on Java 6—I have no way to know without (gasp!) downgrading my JDK. 😄).

Basically the feeling I'm getting is that someone needs to go into the library and just bring it up-to-speed to some modern Java version—update the plugins, fix the unit tests, etc. I could help do that, but only if you say it's OK to move off Java 6. I don't know your feelings about that.

I know as an open-source library maintainer it's easy to think, "oh, I don't want to keep anyone from using my library", and I've had those feelings many times as well. But I think there's a limit and we need to encourage going forward with Java. I would recommend Java 11 at the minimum, but I could work on this if you could at least bear switching to Java 8. I think Java 7 and below would just be too much pain for me without any realistic gain.

[cowtowncoder]

Ok this is unexpected, at least wrt Java 7. As far as I recall things were working with Java 6. And I thought I had actually added Github workflow for running unit tests with matrix build... but not so.

So it definitely sounds like I need to find time to set up modern scaffolding for things, including Maven wrapper as well. Can probably copy much of it from, say, jackson-core.

[cowtowncoder]

Ok, initial parts done; there's now CI for Java 8 and 11, with Maven wrapper.

[cowtowncoder]

Actually need to do #75 to enable JDK 17+ support; closing this as complete.

[garretwilson]

Just circling back to say I'm able to build the project now. Thank you very much.

[cowtowncoder]

@garretwilson No problem; these should already have existed. But better late than never. After getting Jackson 2.16.0-rc1 out (soon) I'll take care of Java 8 upgrade issue, version bump.