Upgrade to Gradle 4.1 for clean JDK 9 build compatibility [SPR-15667]

[spring-issuemaster]

Juergen Hoeller opened SPR-15667 and commented

Gradle 4.1 (currently at M1) is the first Gradle generation to provide official JDK 9 support. Even if Gradle 3.5 and 4.0 work on JDK 9 build 175+ as well, we do want a warning-free experience there eventually.

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Reference URL: spring-projects/spring-boot#9516

Issue Links:

• #18289 Stable module names for Spring Framework jars on JDK 9 module path
• #19083 Upgrade to ASM 6.0
• #20245 Compatibility with JDK 9 release candidate
• #19946 Upgrade to Gradle 3.5
• #20417 Fix Eclipse support in Gradle build
• #20535 Upgrade to Gradle 4.2(.1)

Referenced from: commits 48f95e9

[spring-issuemaster]

Stéphane Nicoll commented

We need to check first if our CI infra is/will be compatible with it in time for the release.

[spring-issuemaster]

Juergen Hoeller commented

In addition to preparing for JDK 9 compatibility in Gradle 4.1, it of course also makes sense to be aligned with Boot 2.0 eventually: spring-projects/spring-boot#9516

[spring-issuemaster]

Juergen Hoeller commented

Putting this into the 5.x backlog since Gradle 3.5 seems to work ok for us on the recent JDK 9 release candidate build (175). What we're really waiting for is Gradle 4.1 with official JDK 9 support, getting rid of the warnings in the log output.

[spring-issuemaster]

Juergen Hoeller commented

Gradle 4.1 RC1 is out now, making it very likely that it'll be GA in time for September.

Seems to work fine for our purposes already, so let's plan an upgrade to it for our 5.0 RC4.