如何刷新我在 ServletContextListener 中設置的 servlet 上下文變量？

Question

我正在使用 Servlet 上下文偵聽器進行大學作業，其中一些上下文變量是從數據庫中設置的。 但是當我將記錄添加到數據庫中的這些列表時，它們不會更新。 他們是一種可以實現的方法嗎？

ServletContextListner：

import edu.witc.pethotel.business.DispositionType;
import edu.witc.pethotel.business.Gender;
import edu.witc.pethotel.business.PetType;
import edu.witc.pethotel.business.State;
import edu.witc.pethotel.data.CustomerDB;
import edu.witc.pethotel.data.TypeDb;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.GregorianCalendar;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyServletContextListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent event) {


        ServletContext sc = event.getServletContext();

        //initialize customer service email
        String custServEmail = sc.getInitParameter("custServEmail");
        sc.setAttribute("custServeEmail", custServEmail);

        //initialize current year
        GregorianCalendar currentDate = new GregorianCalendar();
        int currentYear = currentDate.get(Calendar.YEAR);
        sc.setAttribute("currentYear", currentYear);

        //initialize list of gender
        ArrayList<Gender> genders = TypeDb.getAllGenders();
        sc.setAttribute("genders", genders);

        //initialize list of disposition
        ArrayList<DispositionType> dispositions = TypeDb.getAllDispositions();
        sc.setAttribute("dispositions", dispositions);

        //initialize list of state
        ArrayList<State> states = CustomerDB.getActiveStates();
        sc.setAttribute("states", states);

        //initialize list of pet type
        ArrayList<PetType> petType = TypeDb.getActivePetTypes();
        sc.setAttribute("petTypes", petType);


    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        ServletContext sc = event.getServletContext();

        sc.removeAttribute("genders");
        sc.removeAttribute("dispositions");
        sc.removeAttribute("states");
        sc.removeAttribute("petTypes");
    }
}

Answer 1

在更改數據庫后，此方法可用作 servlet 內部的解決方法，只需覆蓋已更改的上下文變量

request.getServletContext().setAttribute("states", TypeDb.getActiveStates());