我有一个表单，用户可以在其中创建包含信息的事件（例如，事件ID，事件名称。事件位置...）
然后将事件信息存储在数据库中（使用jsp for form，java beans getter和setter，jdbc sql）。
我想检索所有事件信息并将其显示在另一个jsp页面上，但我收到numberformatexception null错误。
我运行了一个测试java文件，它可以正确获取所有事件信息而没有错误，但是当我尝试将其显示在表格内的jsp页面上时，我会收到错误。
当我尝试将以下网址放在地址栏中时
http://localhost:8080/Assignment/addEvent?action=list
我得到数字格式，除了空错误。
WebServlet url模式是“/ addEvent”。
以下是我的相关代码。
EventController Servlet的代码
String action = request.getParameter("action");
if ("list".equalsIgnoreCase(action)) {
// call the query db to get retrieve for all customer
init();
ArrayList events = db.queryEvents();
// set the result into the attribute
request.setAttribute("events", events);
// redirect the result to the listCustomers.jsp
RequestDispatcher rd;
rd = getServletContext().getRequestDispatcher("/AllEventsDisplay.jsp");
rd.forward(request, response);
}
else {
PrintWriter out = response.getWriter();
out.println("Creating event failed!!");
}
AllEventsDisplay.jsp页面
<%
ArrayList<EventBean> events = (ArrayList<EventBean> )request.getAttribute("events");
out.println("<h1>Events</h1>");
out.println("<table border='1'>");
out.println("<tr>");
out.println("<th>Event ID</th> <th> Event Name</th><th> Event Location</th><th> Event Venue</th ><th> Event Date</th ><th> Event Helpers</th ><th> Helper Type</th >");
out.println("</tr>");
// loop through the customer array to display each customer record
for (int i = 0; i < events.size(); i++) {
EventBean c = events.get(i);
out.println("<tr>");
out.println("<td>" + c.getEventID() + "</td>");
out.println("<td>" + c.getEventname() + "</td>");
out.println("<td>" + c.getLocation() + "</td>");
out.println("<td>" + c.getVenue() + "</td>");
out.println("<td>" + c.getDate() + "</td>");
out.println("<td>" + c.getNumofhelper() + "</td>");
out.println("<td>" + c.getHelpertype() + "</td>");
out.println("</tr>");
}
out.println("</table>");
%>
获取事件信息的EventDB方法
public ArrayList queryEvents() {
Connection cnnct = null;
PreparedStatement pStmnt = null;
EventBean cb = null;
ArrayList ca = new ArrayList();
try {
cnnct = getConnection();
String preQueryStatement = "SELECT * FROM EventInfo";
pStmnt = cnnct.prepareStatement(preQueryStatement);
ResultSet rs = null;
rs = pStmnt.executeQuery();
while (rs.next()) {
cb = new EventBean();
cb.setEventID(rs.getString(1));
cb.setEventname(rs.getString(2));
cb.setLocation(rs.getString(3));
cb.setVenue(rs.getString(4));
cb.setDate(rs.getString(5));
cb.setNumofhelper(rs.getInt(6));
cb.setHelpertype(rs.getString(7));
ca.add(cb);
}
} catch (SQLException ex) {
while (ex != null) {
ex.printStackTrace();
ex = ex.getNextException();
}
} catch (IOException ex) {
while (ex != null) {
ex.printStackTrace();
}
}
return ca;
}
请注意NumofHelper是一个整数。
错误堆栈跟踪
WARNING:StandardWrapperValve[EventController]: Servlet.service() for servlet
EventController threw exception
java.lang.NumberFormatExcept ion: null
at java.lang.Integer.parseInt(Integer.java:454)
at java.lang.Integer.parseInt(Integer.java:527)
at ict.servlet.EventController.processRequest(EventController.java:65)
at ict.servlet.EventController.doGet(EventController.java:45)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
at java.lang.Thread.run(Thread.java:724)
信息：访问未经访问的参考文献 信息：访问未经访问的参考文献 信息：访问未经访问的参考文献 信息：在[/ Assignment]加载申请[作业] 信息：分配已在322毫秒内成功部署。
答案 0 :(得分：0)
在EventController.java中，EventHelpers值为空值。您没有检查值是否为null，您尝试解析“null”值。所以它给出了NullPointerException。
int NumberofHelper = 0;
if(EventHelpers != null){
NumberofHelper = Integer.parseInt(EventHelpers);
}
试试这个