Helloworld.java

import java.io.File;
import java.io.InputStream;

public class Authenticate {
	public static void main(String[] args) {

		File jsonKey = new File(KEY_FILE);
		InputStream inputStream = new FileInputStream(jsonKey);
		GoogleCredential credential =
		    GoogleCredential.fromStream(inputStream, HTTP_TRANSPORT, JSON_FACTORY);
	}
}