In the DistributedCacheJoin method with java.io.File, it would be:
File inputTinyFileDescriptor = new File(args[1]);
if(!inputTinyFileDescriptor.exists()) {
	System.out.println("Error: file " + args[1] + "does not exist");
	System.exit(-1);
}

But I read on the web that it could launch an exception with HDFS. So, maybe we can do this in the run method:
FileSystem fs = FileSystem.get(conf);
if (!fs.exists(inputTinyFile)) {
	System.out.println("Error: file " + inputTinyFile + "does not exist");
	System.exit(-1);
}