I wasn't sure if bamboo had a config in addition to the ant/install4j scripts.
It might be worth trying out the attached install4j file. It should be updated for 5.1.9 fully, and includes the other changes you made for j7/8.
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I've also attached Build.patch, which includes a patch form of the spark_install4j_5_1_9.install4j file to replace the current spark.install4j. The Build.patch also finishes iterating spark to use java 7, removes java 5 and 6 as acceptable to ant, and sets the source as java 7 and target as 7 (has to do with compiler optimizations). The patch also updates some old information in the build scripts and also updates the version number to 2.7.0-nightly (so forum nightly-build downloaders can tell a difference).
If committed in a chunk, the commit message should be along the lines of "Update Spark build scripts, and forbid old java versions"
The attached UpdatePluginsForJava7.patch file does just that... it updates all the standard Spark plugins to build with java7, forbid old java versions, and forbid old Spark versions (because java7 built plugins won't work on old spark).
Commit message would be along the lines of "Updated plugins to use java 7, forbid old versions"
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I wouldn't be opposed to having access, if the community agrees.