java - 在 Tomcat 中设置属性时出现 NullPointerException

Question

您好，我需要 Java EE 方面的帮助。我最近使用 Maven 和 Glassfish 在 Netbeans 上用 Java EE 构建了一个项目，一切正常。我们被要求让它在 Tomcat 和 TomEE 下运行，但我不明白为什么我会从 Tomcat 收到此错误。

我从 NullPointerException when setting attribute? 看到了类似的问题

22-Nov-2019 13:33:13.388 SEVERE [http-nio-8080-exec-11] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [JEEServlet] in context with path [/jee-efrei_v3] threw exception
    java.lang.NullPointerException
        at com.controller.JEEServlet.listEmployes(JEEServlet.java:88)
        at com.controller.JEEServlet.logIn(JEEServlet.java:254)
        at com.controller.JEEServlet.doPost(JEEServlet.java:214)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:528)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
        at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)

我试着搜索了一下，一些建议是添加:

1. context.xml 文件

<?xml version="1.0" encoding="UTF-8"?>
<!--
To change this license header, choose License Headers in Project Properties.
To change this template file, choose Tools | Templates
and open the template in the editor.
-->

<Context>
    <Resource
        name="jdbc/jeeprj" type="javax.sql.DataSource"
        maxActive="100" maxIdle="30" maxWait="10000" 
        url="jdbc:mysql://localhost:3306/jeeprj?zeroDateTimeBehavior=convertToNull"
        driverClassName="com.mysql.jdbc.Driver"
        username="jee" password="jeeprj"
    />
</Context>

1. 将 mysql 连接添加到 Tomcat 的库中
2. 通过添加 resource-env-ref 编辑我的 web.xml

这是我的web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
     version="3.1">
    <welcome-file-list>
        <welcome-file>/WEB-INF/login.jsp</welcome-file>
    </welcome-file-list>
    <servlet>
        <servlet-name>JEEServlet</servlet-name>
        <servlet-class>com.controller.JEEServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>JEEServlet</servlet-name>
        <url-pattern>/JEEServlet</url-pattern>
    </servlet-mapping>
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
    <resource-env-ref>
        <resource-env-ref-name>jdbc/jeeprj</resource-env-ref-name>
        <resource-env-ref-type>javax.sql.DataSource</resource-env-ref-type>
    </resource-env-ref>
</web-app>

这是我的persistence.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.1" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
  <persistence-unit name="com.jvprj_jee-efrei_maven_war_1.0-SNAPSHOTPU" transaction-type="JTA">
    <provider>org.apache.openjpa.persistence.PersistenceProvider</provider>
    <jta-data-source>jdbc/jeeprj</jta-data-source>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties/>
  </persistence-unit>
</persistence>

这里是tomcat在控制台指出的各个区域:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.controller;

import com.dao.EmployeDAOLocal;
import com.model.Jeeprj;
import java.io.IOException;
import java.io.PrintWriter;
import javax.ejb.EJB;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 *
 * @author EKEUMOU
 */
@WebServlet(name = "JEEServlet", urlPatterns = {"/JEEServlet"})
public class JEEServlet extends HttpServlet {

    @EJB
    private EmployeDAOLocal employeDao;

    boolean selected = true;

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        try {

            String theCommand = request.getParameter("action");

            if (theCommand == null){
                theCommand = "LIST";
            }

            switch(theCommand){
                case "LIST":
                case "Voir Liste":
                    listEmployes(request, response);
                    break;
                case "Ajouter":
                    showFormAddEmploye(request, response);
                    break;
                case "Modifier":
                    showFormModifyEmploye(request, response);
                    break;
                case "Valider":
                    updateEmploye(request, response);
                    break;
                case "Logout":
                    logOut(request, response);
                    break;    
                case "Supprimer":
                    deleteEmploye(request, response);
                    break;
                case "Details":
                    loadEmploye(request,response);
                    break;
                 case "UPDATE_EMPLOYE":
                    updateEmploye(request,response);
                    break;
                default:
                    listEmployes(request, response);
            }

        }
        catch (IOException | ServletException exc) {
            throw new ServletException(exc);
        }
    }

    private void listEmployes(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession(true);
        String userName = (String) session.getAttribute("userName");
        if (userName.equals("empl"))
            listEmployesEmpl(request, response);
        else {
            request.setAttribute("allEmployes", employeDao.getAllEmployes());
            RequestDispatcher dispatcher = request.getRequestDispatcher("WEB-INF/list-employe.jsp");
            dispatcher.forward(request, response);
        }
    }

    private void listEmployesEmpl(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setAttribute("allEmployes", employeDao.getAllEmployes());
        RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("WEB-INF/list-employe_empl.jsp");
        dispatcher.forward(request, response);
    }

    private void showFormAddEmploye(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        RequestDispatcher dispatcher = request.getRequestDispatcher("WEB-INF/add-employe-form.jsp");
        dispatcher.forward(request, response);
    }

    private void addEmploye(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String nom = request.getParameter("nom");
        String prenom = request.getParameter("prenom");
        String telDom = request.getParameter("telDom");
        String telPor = request.getParameter("telPor");
        String telPro = request.getParameter("telPro");
        String adresse = request.getParameter("adresse");
        String codePostal = request.getParameter("codePostal");
        String ville = request.getParameter("ville");
        String email = request.getParameter("email");

        Jeeprj theEmploye = new Jeeprj(nom, prenom, telDom, telPor, telPro, adresse, codePostal, ville, email);
        employeDao.addEmploye(theEmploye);

        listEmployes(request, response);
    }

    private void deleteEmploye(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String theEmployeStrId = request.getParameter("selectedEmploye");
        int theEmployeId = 0;

        //if(theEmployeStrId!=null && !theEmployeStrId.equals("")){
        try{
            theEmployeId=Integer.parseInt(theEmployeStrId);
            request.getSession().setAttribute("result", true);
            employeDao.deleteEmploye(theEmployeId);
        }catch (NumberFormatException ex) {
            request.getSession().setAttribute("result", false);
        }

        listEmployes(request, response);

    }

    private void loadEmploye(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        HttpSession session = request.getSession(true);
        String theEmployeStrId = request.getParameter("selectedEmploye");
        int theEmployeId = 0;
        String userName = (String) session.getAttribute("userName");

        if(theEmployeStrId != null && !theEmployeStrId.equals("")){
            theEmployeId=Integer.parseInt(theEmployeStrId);


            Jeeprj theEmploye =  employeDao.getEmploye(theEmployeId);
            session.setAttribute("THE_EMPLOYE", theEmploye);

            if (userName.equals("admin")) {
                RequestDispatcher dispatcher = request.getRequestDispatcher("WEB-INF/details-employe-form.jsp");
                dispatcher.forward(request, response);
            }
            else {
                RequestDispatcher dispatcher = request.getRequestDispatcher("WEB-INF/details-employe-form_empl.jsp");
                dispatcher.forward(request, response);
            }

        }else{
            if (userName.equals("admin"))
                listEmployes(request, response);
            else
                listEmployesEmpl(request, response);
        }


    }

    private void updateEmploye(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        int employeId = Integer.parseInt(request.getParameter("employeId"));
        String nom = request.getParameter("nom");
        String prenom = request.getParameter("prenom");
        String telDom = request.getParameter("telDom");
        String telPor = request.getParameter("telPor");
        String telPro = request.getParameter("telPro");
        String adresse = request.getParameter("adresse");
        String codePostal = request.getParameter("codePostal");
        String ville = request.getParameter("ville");
        String email = request.getParameter("email");

        Jeeprj theEmploye = new Jeeprj(employeId, nom, prenom, telDom, telPor, telPro, adresse, codePostal, ville, email);
        employeDao.editEmploye(theEmploye);

        listEmployes(request, response);
    }

    private void showFormModifyEmploye(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       /*HttpSession session = request.getSession(true);
       Jeeprj ub = (Jeeprj) session.getAttribute("THE_EMPLOYE");
       session.setAttribute("THE_EMPLOYE", ub);*/
       RequestDispatcher dispatcher = request.getRequestDispatcher("WEB-INF/modify-employe-form.jsp");
       dispatcher.forward(request, response);  
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        try {

            String theCommand = req.getParameter("action");

            if (theCommand == null){
                theCommand = "Login";
            }

            switch(theCommand){
                case "Login":
                    logIn(req, resp);
                    break;
                default:
                    logIn(req, resp);
            }

        }
        catch (IOException | ServletException exc) {
            throw new ServletException(exc);
        }
    }



    protected void logIn(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String userName = req.getParameter("username");
        String password = req.getParameter("password");
        if (userName != null && userName.trim().length() > 0 && 
                password != null && password.trim().length() > 0) {
            System.out.println(userName + " : " + password);
            if (userName != null && userName.length() != 0 && (userName.equals("admin") || userName.equals("empl")) && 
                    password != null && password.length() != 0 && (password.equals("admin") || password.equals("empl"))) {
                if (req.getParameter("remember") != null) {
                    String remember = req.getParameter("remember");
                    System.out.println("remember : " + remember);
                    Cookie cookUserName = new Cookie("cookUserName", userName.trim());
                    Cookie cookPassword = new Cookie("cookPassword", password.trim());
                    Cookie cookRemember = new Cookie("cookRemember", remember.trim());
                    cookUserName.setMaxAge(60*60*24*3); // 3days
                    cookPassword.setMaxAge(60*60*24*3);
                    cookRemember.setMaxAge(60*60*24*3);
                    resp.addCookie(cookUserName);
                    resp.addCookie(cookPassword);
                    resp.addCookie(cookRemember);
                }
                HttpSession httpSession = req.getSession();
                httpSession.setAttribute("sessionUser", userName.trim());
                httpSession.setAttribute("userName", userName);
                if (userName.equals("admin"))
                    listEmployes(req, resp);
                else
                    listEmployesEmpl(req, resp);

            } else {
                System.out.println("Erreur d'Authentification");
                req.setAttribute("message", "Erreur d'Authentification");
                RequestDispatcher requestDispatcher = req.getRequestDispatcher("WEB-INF/login.jsp");
                requestDispatcher.forward(req, resp);
            }
        } else {
            System.out.println("Nom d'Utilisateur et Mot de Passe Requis !");
            req.setAttribute("message", "Nom d'Utilisateur et Mot de Passe Requis !");
            RequestDispatcher requestDispatcher = req.getRequestDispatcher("WEB-INF/login.jsp");
            requestDispatcher.forward(req, resp);
        }
    }

    private void logOut(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        Cookie cookUserName = new Cookie("cookUserName", null);
        Cookie cookPassword = new Cookie("cookPassword", null);
        Cookie cookRemember = new Cookie("cookRemember", null);
        cookUserName.setMaxAge(0);
        cookPassword.setMaxAge(0);
        cookRemember.setMaxAge(0);
        response.addCookie(cookUserName);
        response.addCookie(cookPassword);
        response.addCookie(cookRemember);

        HttpSession httpSession = request.getSession();
        httpSession.invalidate();
        request.setAttribute("message", "Deconnexion réussie !");
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("WEB-INF/login.jsp");
        requestDispatcher.forward(request, response);
    }



}

提前感谢您的各种回答。

Answer 1

这里创建 employedAo bean 似乎有问题:

@EJB
private EmployeDAOLocal employeDao;

由于某种原因，它的实例没有被创建。检查该类是否所有不可替代的注解等。