Question

当我在.get（）方法中放置一个属性时，我似乎正在收到一个nullpointer异常，当我调用它的entiire集合时，它打印出我想要的代码。如果有人可以帮助它将非常感谢我新的堆栈溢出。

        session.setAttribute("AvailableLessons",availableLessons.getLessons()); will print out contents of the hashmaps. 

        session.setAttribute("AvailableLessons",availableLessons.getLessons(Lesson.description)); will return null pointer expcetion and the property is a db column name and when i step through it, will have a value in the property.

这是代码的其余部分：

        private LessonTimetable availableLessons =  new LessonTimeTable();
        HttpSession session = request.getSession();
        session.setAttribute("Username", username);
        response.sendRedirect("/coursework/LessonTimetableView.jspx");
        String printOut = ((String) session.getAttribute("Username"));
        out.print("You are logged in as " + printOut);
        session.setAttribute("AvailableLessons",availableLessons.getDescription());

这是堆栈跟踪：

java.lang.NullPointerException
controller.Controller.processRequest(Controller.java:79)
controller.Controller.doPost(Controller.java:88)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)

在hashmap.get（）方法上获取空指针异常

0 个答案: