Bugfix/jdk9 build fixes

[nhojpatrick]

Linked to #1233

With Java 9, it drops support for Java 5 i.e. -source 1.5 and -target 1.5. So this pull request updates updates the min Java version needed to 1.6.

Two maven plugins, maven-jar-plugin and maven-javadoc-plugin also have issues with Java 9.

Once apache/maven-plugins#76 is merged it will depending on a fixed version of plexus-archiver (see codehaus-plexus/plexus-archiver#12).

[kcooney]

@nhojpatrick thanks for the fix! We don't want to change the required JDK version on the master branch, because master will be used for JUnit 4.13. I believe we changed the required JDK version on the junit5 branch. Is the bug reproducible there? If so, can you please redo these changes on that branch?

[marcphilipp]

@kcooney The junit5 branch will most probably never be released since we're working on JUnit 5 (alpha) in the junit-lambda repository.

[kcooney]

@marcphilipp I thought we agreed to review the changes on the junit5 branch?

In any case, we shouldn't upgrade the required JDK version in a 4.x release.

Luckily, JDK 9 isn't scheduled to be released until September, so we have time.

[nhojpatrick]

Tried the junit-team:junit:junit5 branch but it uses older versions of the plugins than junit-team:junit:master does.

Checkout junit-team:junit-lambda:master but don't have gradle installed so will leave it for the time being.

[kcooney]

We haven't done a merge from master to junit5 in a while. I personally see some value in some of the changes in the junit5 branch. Will discuss with the other maintainers off-thread

[nhojpatrick]

Regarding the September comment, it does seam a long way away. But what about other projects that might want to use JUnit and also support Java 9... when Java 9 is generally available.

Let me know what is decided regarding junit5 and also Java 9, and when I've free time I'll try and help out.

[kcooney]

@nhojpatrick unless I'm misunderstanding the changes, they only affect the ability to build JUnit; Java 9 users should be able to use the prebuilt 4.12 jars, correct? If so, I think we can wait until we can use non-snapshot jars of these plugins.

[Tibor17]

@nhojpatrick javac 1.6 was here discussed several times. JUnit4 will never have it for sure.
Regarding JDK 9 this does not touch users because ordinal jar will work in JDK9 and therefore we do not need JDK9 to build JUnit. I think Travis is good enough with JDK 7/8 until JUnit4 has died.

[kcooney]

since the jars can still be used, I vote we close this.

[marcphilipp]

Agreed.