【发布时间】：2015-10-14 21:07:49
【问题描述】：
每当我尝试使用 jdbc 将值插入到表中时，我都会得到一个空指针，我根本不知道为什么。
它应该像这样工作：我在 JSP 上的文本字段中输入数据。当我按下提交按钮时，servlet 应该将参数从文本字段发送到数据访问类。与数据库的连接有效，因为我可以从 x 中选择 * 作为简单测试。字符串应添加到以下 SQL 表中：
create table bedrijf(
bedrijfID int not null AUTO_INCREMENT,
naam varchar(80) not null,
postcode varchar(10),
gemeente varchar(50),
website varchar(50),
primary key (bedrijfID)
);
JSP 发送参数：
<table id="indextabel">
<form action="StartServlet" method="post">
<tr>
<td><label for="bedrijfnaam">Naam bedrijf</label></td>
<td><input type="text" name="bedrijfnaam" id="bedrijfnaam"/></td>
</tr>
<tr>
<td><label for="postcode">Postcode</label></td>
<td><input type="text" name="postcode" id="postcode"/></td>
</tr>
<tr>
<td><label for="gemeente">Gemeente</label></td>
<td><input type="text" name="gemeente" id="gemeente"/></td>
</tr>
<tr>
<td><label for="website">Website</label></td>
<td><input type="text" name="website" id="website"/></td>
</tr>
<tr>
<td><input type="submit" value="Registreer nu" name="nieuwbedrijf-validate"/></td>
</tr>
</form>
</table>
数据访问类：
import info.toegepaste.www.beans.Account;
import info.toegepaste.www.beans.Alumnus;
import info.toegepaste.www.beans.Bedrijf;
import info.toegepaste.www.beans.Event;
import info.toegepaste.www.beans.Inschrijving;
import info.toegepaste.www.beans.Richting;
import java.sql.Connection;
import java.util.Date;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
public class DABedrijf {
private Connection connection = null;
public DABedrijf(String url, String login, String password, String driver) throws ClassNotFoundException, SQLException {
// Class.forName("com.mysql.jdbc.Driver");
Class.forName(driver);
connection = DriverManager.getConnection(url, login, password);
}
public void close() throws SQLException {
if (connection != null) {
connection.close();
}
}
public ArrayList<Bedrijf> getAlleBedrijven(){
Statement statement = null;
ResultSet resultSet = null;
ArrayList<Bedrijf> bedrijven = new ArrayList<>();
try {
statement = connection.createStatement();
resultSet = statement.executeQuery("select * from bedrijf order by bedrijf.naam");
while (resultSet.next()) {
Bedrijf bedrijf = new Bedrijf();
bedrijf.setBedrijfid(resultSet.getInt("bedrijf.bedrijfid"));
bedrijf.setNaam(resultSet.getString("bedrijf.naam"));
bedrijf.setPostcode(resultSet.getString("bedrijf.postcode"));
bedrijf.setGemeente(resultSet.getString("bedrijf.gemeente"));
bedrijf.setWebsite(resultSet.getString("bedrijf.website"));
bedrijven.add(bedrijf);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
statement.close();
if (resultSet != null) {
resultSet.close();
}
} catch (SQLException e) {
}
}
return bedrijven;
}
public boolean bedrijfInsert(String naam, String postcode, String gemeente, String website) {
boolean resultaat = true;
PreparedStatement statement = null;
try {
statement = connection.prepareStatement("Insert into bedrijf values (null,?,?,?,?)");
statement.setString(1, naam);
statement.setString(2, postcode);
statement.setString(3, gemeente);
statement.setString(4, website);
statement.executeUpdate();
} catch (Exception e) {
resultaat = false;
e.printStackTrace();
} finally {
try {
if (statement != null) {
statement.close();
}
} catch (SQLException e) {
}
}
return resultaat;
}
}
Servlet：
/*
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* and open the template in the editor.
*/
package info.toegepaste.www;
import info.toegepaste.www.beans.Account;
import info.toegepaste.www.beans.Bedrijf;
import info.toegepaste.www.beans.Alumnus;
import info.toegepaste.www.beans.Event;
import info.toegepaste.www.beans.Inschrijving;
import info.toegepaste.www.beans.Richting;
import info.toegepaste.www.dataaccess.DAAccount;
import info.toegepaste.www.dataaccess.DAAlumnus;
import info.toegepaste.www.dataaccess.DABedrijf;
import info.toegepaste.www.dataaccess.DAEvent;
import info.toegepaste.www.dataaccess.DAInschrijving;
import info.toegepaste.www.dataaccess.DARichting;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Date;
import java.sql.SQLException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Locale;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
@WebServlet(name = "StartServlet", urlPatterns = {"/StartServlet"},
initParams = {
@WebInitParam(name = "url", value = "jdbc:mysql://localhost/lesson"),
@WebInitParam(name = "login", value = "dba"),
@WebInitParam(name = "password", value = "sql"),
@WebInitParam(name = "driver", value = "com.mysql.jdbc.Driver")})
public class StartServlet extends HttpServlet {
private DAAccount daaccount = null;
private DAAlumnus daalumnus = null;
private DABedrijf dabedrijf = null;
private DAEvent daevent = null;
private DAInschrijving dainschrijving = null;
private DARichting darichting = null;
@Override
public void init() throws ServletException {
try {
String url = getInitParameter("url");
String password = getInitParameter("password");
String login = getInitParameter("login");
String driver = getInitParameter("driver");
if (daaccount == null) {
daaccount = new DAAccount(url, login, password, driver);
}
if (daalumnus == null) {
daalumnus = new DAAlumnus(url, login, password, driver);
}
if (dabedrijf == null) {
dabedrijf = new DABedrijf(url, login, password, driver);
}
if (daevent == null) {
daevent = new DAEvent(url, login, password, driver);
}
if (dainschrijving == null) {
dainschrijving = new DAInschrijving(url, login, password, driver);
}
if (darichting == null) {
darichting = new DARichting(url, login, password, driver);
}
} catch (ClassNotFoundException | SQLException e) {
throw new ServletException(e);
}
}
@Override
public void destroy() {
try {
if (daaccount != null) {
daaccount.close();
}
if (daalumnus != null) {
daalumnus.close();
}
if (dabedrijf != null) {
daevent.close();
}
if (dainschrijving != null) {
dainschrijving.close();
}
if (darichting != null) {
darichting.close();
}
} catch (SQLException e) {
}
}
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession();
RequestDispatcher rd = null;
if (request.getParameter("registreer-button") != null) {
ArrayList<Event> eventen = daevent.getAlleEventen();
ArrayList<Bedrijf> bedrijven = dabedrijf.getAlleBedrijven();
ArrayList<Richting> richtingen = darichting.getAlleRichtingen();
request.setAttribute("eventen", eventen);
request.setAttribute("bedrijven", bedrijven);
request.setAttribute("richtingen", richtingen);
rd = request.getRequestDispatcher("registreer.jsp");
} else if (request.getParameter("inlog-knop") != null) {
rd = request.getRequestDispatcher("inlog.jsp");
} else if (request.getParameter("nieuwbedrijf-validate") != null) {
String naam = request.getParameter("bedrijfnaam");
String postcode = request.getParameter("postcode");
String gemeente = request.getParameter("gemeente");
String website = request.getParameter("website");
if(dabedrijf.bedrijfInsert(naam, postcode, gemeente, website));{
ArrayList<Bedrijf> bedrijven = dabedrijf.getAlleBedrijven();
request.setAttribute("bedrijven", bedrijven);
rd = request.getRequestDispatcher("registreer.jsp");}
} else if (request.getParameter("nieuwbedrijf-knop") !=null) {
rd = request.getRequestDispatcher("nieuwbedrijf.jsp");
} else if (request.getParameter("registreer-validatie") !=null) {
int richtingid = Integer.parseInt(request.getParameter("richting"));
int bedrijfid = Integer.parseInt(request.getParameter("bedrijf"));
String voornaam = request.getParameter("voornaam");
String achternaam = request.getParameter("achternaam");
String emailprive = request.getParameter("emailprive");
String afstudeerjaar = request.getParameter("afstudeerjaar");
String date = request.getParameter("date");
java.sql.Date dateConvert = java.sql.Date.valueOf(date);
String inlognaam = request.getParameter("inlognaam");
String paswoord = request.getParameter("paswoord");
if(daaccount.accountInsert(inlognaam, paswoord));{
ArrayList<Account> accounts = daaccount.getAlleAccounts();
request.setAttribute("accounts", accounts);}
rd = request.getRequestDispatcher("registratiegelukt.jsp");
// if(daaccount.accountInsert(voornaam, date));{
// rd = request.getRequestDispatcher("registratiegelukt.jsp");
//
// }
// if(daalumnus.alumnusInsert(richtingid, bedrijfid, voornaam, achternaam, emailprive, afstudeerjaar, dateConvert));{
// rd = request.getRequestDispatcher("registratiegelukt.jsp");}
// } else {
// request.setAttribute("fout", "Toevoegen alumni niet gelukt!");
// rd = request.getRequestDispatcher("index.jsp");
// }
}
rd.forward(request, response);
}
我真的不知道问题出在哪里，不胜感激。
堆栈跟踪：
Warning: StandardWrapperValve[StartServlet]: Servlet.service() for servlet StartServlet threw exception
java.lang.NullPointerException
at org.apache.jsp.registreer_jsp._jspService(registreer_jsp.java:135)
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 info.toegepaste.www.StartServlet.processRequest(StartServlet.java:182)
at info.toegepaste.www.StartServlet.doPost(StartServlet.java:212)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
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:415)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:282)
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:201)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:175)
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:284)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:561)
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$Worker.doWork(AbstractThreadPool.java:565)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:545)
at java.lang.Thread.run(Thread.java:745)
【问题讨论】：
-
请显示堆栈跟踪。
-
“我真的不知道问题出在哪里”。堆栈跟踪应该告诉你 NPE 来自哪里，确定吗？
-
我已经添加了警告列表，但是我没有得到更明智的选择。抱歉，我是新手。
-
堆栈跟踪非常具有描述性。你在 StartServlet.java 第 182 行有什么
-
感谢您到目前为止的回答。我已经用整个 servlet 编辑了原始帖子。第 182 行是 rd.forward(request, response);
标签： java jsp servlets jdbc insert