Building on a system with an unsupported Java version fails silently

[Neil Roberts]

The spawned process in build/transforms/optimizer/sendJob.js that runs the closure compiler will fail on a system running with Java previous to version 7. The build tool will fail with an error that looks like this:

Error: read ECONNRESET
    at exports._errnoException (util.js:1012:11)`
    at Pipe.onread (net.js:563:26) code: 'ECONNRESET', errno: 'ECONNRESET', syscall: 'read' }
Error: read ECONNRESET
    at exports._errnoException (util.js:1012:11)
    at Pipe.onread (net.js:563:26)

But if you log the output from the spawned process, the message will look like this:

Exception in thread "main" java.lang.UnsupportedClassVersionError: com/google/javascript/jscomp/SourceFile : Unsupported major.minor version 51.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:643)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)

Additional error logging should be added to detect other potential errors within the spawned process as well as a way to notify users that Java 7 is required to run the build tool.