nielsbasjes opened a new pull request #12808:
URL: https://github.com/apache/flink/pull/12808


   ## What is the purpose of the change
   
   In the pom.xml (in various places) the **user** property `java.version` is 
used containing the version of the jdk that is to be used.
   
   There is however also a **system** property `java.version` which contains 
the actually used jdk version to build the software.
   
   As a consequence some things become very confusing and brittle.
   
   For example the profile activation in maven can be done using the <jdk> 
which looks at the system property java.version which is different from the 
user property java.version.
   
   
https://github.com/apache/maven/blob/master/maven-compat/src/main/java/org/apache/maven/profiles/activation/JdkPrefixProfileActivator.java#L36
   
   Also the maven-enforcer-plugin is used with the clause
   ```
   <requireJavaVersion>
      <version>${java.version}</version>
   </requireJavaVersion>
   ```
   Here also this rule effectively compares the system property with the user 
property with the same name to see if they match.
   
   
https://github.com/apache/maven-enforcer/blob/master/enforcer-rules/src/main/java/org/apache/maven/plugins/enforcer/RequireJavaVersion.java#L46
   
https://github.com/apache/commons-lang/blob/master/src/main/java/org/apache/commons/lang3/SystemUtils.java#L529
   So although it works it also makes it impossible to debug which java.version 
is used by the various plugins as the value shown on the screen is always a 
different value.
   
   The change is very simple: do no use java.version as the name for a user 
property.
   
   ## Brief change log
   
   Rename any use of the user property `java.version` to `target.java.version` 
to indicate that this is the java runtime version for which we aim to build the 
software.
   
   ## Verifying this change
   
   This change is a trivial rework / code cleanup without any test coverage.
   
   The regular build should simply work as normal.
   
   ## Does this pull request potentially affect one of the following parts:
   
     - Dependencies (does it add or upgrade a dependency): **no**
     - The public API, i.e., is any changed class annotated with 
`@Public(Evolving)`: **no**
     - The serializers: **no**
     - The runtime per-record code paths (performance sensitive): **no**
     - Anything that affects deployment or recovery: JobManager (and its 
components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: **no**
     - The S3 file system connector: **no**
   
   ## Documentation
   
     - Does this pull request introduce a new feature? **no**
   


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