I recently encountered a build environment behavior that I need to better understand:
Overview of my freshly installed workstation:
C:\\Program Files\\Java\\jdk1.8.0_131\\
C:\\Program Files\\Java
the following: jdk1. 7 .0_45, jre1. 7 .0_76, jre1. 7 .0_79. My Eclipse's Window > Preferences > Java > Installed JREs
now looks:
Execution environments are standard (ie I have not added any):
Now, when I right-click the project's build.xml
and run that Ant Build... I can see that an execution environment that uses jre7
(jdk1. 7 .0_80) as its default, is selected:
So, when I click Apply, then Run, it will use a Java 7 compiler, right?
Wrong. For some strange reason, all .class
files generated by this build have a major_version of Java 8!
I solved this problem by brute-forcing Ant to use Javac 1.7, via build.xml:
<property name="ant.build.javac.source" value="1.7"/>
<property name="ant.build.javac.target" value="1.7"/>
My question is: Why would a build in Eclipse running under JDK8 default to JRE8 despite Execution Environment set to JDK7 ?
IOW, is this a documented feature? If so, where can I learn more about this?
Update:
Thanks to the answer below, I tried to verify the role of %JAVA_HOME% in Ant's execution. Externally changing my workstation's %JAVA_HOME% system variable would be defeating the purpose of my setup, so I tried changing %JAVACMD% only. That didn't help. So, I echoed relevant env vars in my build.xml
:
<target name="jdk_version_validation">
<echo message="Java Version: ${java.version}" />
<echo message="Java home: ${java.home}" />
<echo message="JAVA_HOME: ${env.JAVA_HOME}" />
<echo message="JAVACMD: ${env.JAVACMD}" />
</target>
and this is what I got:
jdk_version_validation:
[echo] Java Version: 1.7.0_80
[echo] Java home: C:\Program Files\Java\jre7
[echo] JAVA_HOME: C:\Program Files\Java\jdk1.8.0_131\
[echo] JAVACMD: C:\Program Files\Java\jdk1.7.0_80\bin
Without the brute-force property overriding described above, this still produces Java 8 class files. Amazing.
A lot of those things you list appear to be JREs (which don't contain a javac
compiler). So Ant is probably falling back on using the 1.8 JDK listed in JAVA_HOME.
You could try using the JavaSE-1.7 Execution Evironment and actually select the one JDK you have as the default in the 'Compatible JREs' list.
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