如何刷新我在 ServletContextListener 中设置的 servlet 上下文变量？

Posted 2023-02-26

【中文标题】如何刷新我在 ServletContextListener 中设置的 servlet 上下文变量？

【英文标题】：How can i refresh servlet context variables i have set in a ServletContextListener?

【发布时间】：2020-07-28 20:06:44

【问题描述】：

我正在使用 Servlet 上下文侦听器进行大学作业，其中一些上下文变量是从数据库中设置的。但是当我将记录添加到数据库中的这些列表时，它们不会更新。他们有办法做到这一点吗？

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");
    

【参考方案1】：

在更改数据库后，此方法可用作 servlet 内部的解决方法，只需覆盖已更改的上下文变量

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