[FIXED] Method introduced in java 9 is compiled using compiler target java 8

Issue

I'm experiencing an odd behavior in maven as well as in eclipse itself. Even though i configured my project to be compiled in Java 1.8, I can compile and run (eclipse) a piece of code that was introduced in Java 9

<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>

The code line in question:

LocalTime.ofInstant(cal.toInstant(), cal.getTimeZone().toZoneId());

I'm using Oracle's JDK 11 locally for compiling and running in eclipse without any errors. When i package it into a docker container using openjdk:8-jdk-alpine it will boot up, but throw the following Exception when I call the method:

java.lang.NoSuchMethodError: java.time.LocalTime.ofInstant(Ljava/time/Instant;Ljava/time/ZoneId;)Ljava/time/LocalTime

How can I avoid and identify these situations before they go to testing? Am I doing something wrong or is it a bug in the build system or in JDK11?

thanks in advance

Solution

The source option specifies that the source code must be compatible with Java 8, the target option that the classes should be compatible with Java 8. However, you will still compile with the Java 11 class library if you build with Java 11 and then you can get errors like the one you have.

There are two good solutions. One is to use the Maven toolchains plugin and build with Java 8. Then you can have multiple Java versions installed and Maven will use the configured one on a per-project basis.

The other is to use the new release and testRelease options. They will build with API classes from the given release. Just add <release>1.8</release>.

Answered By - ewramner
Answer Checked By - Willingham (JavaFixing Volunteer)