Servlets :: Checkbox Not Working Right

I am trying to finish this servlet that adds a new course to my courses display. im using a check box so the user can pick what the prerequisite are for the new course they want to add. so if they check cs201 , it will add cs201 as a prerequisite for that new course.

for some reason my checkbox will only add the first checkbox that is clicked. like if i add a subject , and click the check boxs for cs203 , cs202, and cs201. it will only grab cs201 and add it to my course display. it wont grab all 3. how can i grab the other info thats checked?

package cs320Homework1.servlet;
 import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
 import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;

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