JAVA: подключение к JavaDB из среды IDE NetBeans
Здравствуйте, спасибо, что прочитали это.
Я изучил этот учебник, чтобы узнать, как использовать встроенную базу данных NetBeans:
https://netbeans.org/kb/docs/ide/java-db.html
И я хотел бы подключиться к JavaDB со страницы JSP, потому что именно там я хотел бы показать информацию, чтобы проверить, работает ли соединение.
Ранее я сохранял созданные пользователем курсы, от формы до HttpSession.
Вот БД и таблица, о которой мы говорим:
Детали подключения:
URL базы данных: jdbc:derby://localhost:1527/cursosПользователь: nbuserПроходить: nbuserСхема по умолчанию: APP Имя таблицы: Cursos
Код, который я попробовал:
<%@page import="java.sql.Statement"%>
<%@page import="java.sql.DriverManager"%>
<%@page import="java.sql.ResultSet"%>
<%@page import="java.sql.Connection"%>
<%@page import="org.Curso"%>
<%@page import="java.util.Iterator"%>
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.Enumeration"%>
<html>
<head>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css">
</head>
<body>
<table width="100%" border=1>
<tr>
<th style="padding: 8px">Titulo</th>
<th style="padding: 8px">Autor</th>
<th style="padding: 8px">Asignatura</th>
<th style="padding: 8px">Duracion</th>
<th style="padding: 8px">Video</th>
</tr>
<%
Class.forName("org.apache.derby.jdbc.ClientDriver");
Connection connection = null;
ResultSet resultSet = null;
String host = "jdbc:derby://localhost:1527/cursos";
String user = "nbuser";
String pass = "nbuser";
try {
connection = DriverManager.getConnection(host, user, pass);
Statement statement = connection.createStatement();
String sql = "SELECT * FROM APP.CURSOS";
resultSet = statement.executeQuery(sql);
while (resultSet.next()) {
out.println(resultSet.getString(1) + " " + resultSet.getString(2) + " " + resultSet.getString(3)
+ " " + resultSet.getInt(4) + " " + resultSet.getInt(5) + "<br>");
}
} catch (Exception e) {
out.print("Error connecting to DB");
} finally {
resultSet.close();
connection.close();
}
%>
<% if (session.getAttribute("cursos") != null) {%>
<% ArrayList cursos = (ArrayList) session.getAttribute("cursos");
Iterator i = cursos.iterator();
int current = 0;
while (i.hasNext()) {
Curso cursoActual = (Curso) i.next();
%>
<tr>
<td><%= cursoActual.getTitulo()%></td>
<td><%= cursoActual.getAutor()%></td>
<td><%= cursoActual.getAsignatura()%></td>
<td><%= cursoActual.getDuracion()%></td>
<td><a href="<%= cursoActual.getVideo()%>">Video</a></td>
</tr>
<%
current++;
}
%>
<br/>
<% }%>
</table>
</body>
</html>
Ожидаемый результат будет состоять в том, чтобы регистры БД отображались в верхней части страницы, а затем сохранялись в HTTPSession.
Данный результат является пустой страницей.
Журнал сервера Glassfish говорит:
Advertencia: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.CourseInfo_jsp._jspService(CourseInfo_jsp.java:103)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:411)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:473)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:377)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:875)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:739)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:575)
at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:546)
at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:428)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:378)
at frontController.FrontCommand.forward(FrontCommand.java:35)
at frontController.CourseInfoCommand.process(CourseInfoCommand.java:83)
at org.FrontServlet.processRequest(FrontServlet.java:43)
at org.FrontServlet.doGet(FrontServlet.java:103)
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:416)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:283)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:206)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:180)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:283)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
at java.lang.Thread.run(Thread.java:745)
Grave: org.apache.jasper.JasperException: java.lang.NullPointerException
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:440)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:473)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:377)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:875)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:739)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:575)
at org.apache.catalina.core.ApplicationDispatcher.doDispatch(ApplicationDispatcher.java:546)
at org.apache.catalina.core.ApplicationDispatcher.dispatch(ApplicationDispatcher.java:428)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:378)
at frontController.FrontCommand.forward(FrontCommand.java:35)
at frontController.CourseInfoCommand.process(CourseInfoCommand.java:83)
at org.FrontServlet.processRequest(FrontServlet.java:43)
at org.FrontServlet.doGet(FrontServlet.java:103)
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:416)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:283)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:206)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:180)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:283)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at org.apache.jsp.CourseInfo_jsp._jspService(CourseInfo_jsp.java:103)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:411)
... 44 more
Исходя из этого, мы можем думать, что проблема в подключении к БД из-за строки: at frontController.CourseInfoCommand.process(CourseInfoCommand.java:83)
Это тот, куда мы перенаправляем, пересылаем на CourseInfo.jsp:
forward("/CourseInfo.jsp");
Чтобы проверить предыдущие гипотезы, которые утверждали, что новое соединение с БД вызывало пустую страницу, я удаляю этот код в CourseInfo.jsp и мы видим, что курсы сохраняются в сеансе после их создания:
Не могли бы вы помочь мне исправить это соединение с БД?