According to javadoc ZipExporter.exportTo(java.io.File target) should fail if the target file exists. It does not seem to be the case, the target file is rewritten silently instead.
Also, the javadoc is confusing. It says:
Exports provided archive as in an implementation-specific format, written to the specified File target. If the target exists this call will fail with IllegalArgumentException. However later it says that FileExistsException is thrown in such case.