我要访问我的数据库以获取信息，并且它会继续抛出空的异常。
我呼叫对象和技术人员对象/
addTech.jsp：
<%@page import="com.example.backend.BackendFactory"%>
<%@page import="java.util.ArrayList"%>
<%@page import="com.example.model.*"%>
<%@ page language="java" contentType="text/html; charset=windows-1255"
pageEncoding="windows-1255"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Adding Tech</title>
</head>
<%
String TechId, TechName, TechUserName, TechPass, TechPassVer, TechRank, TechSecQ, TechSecA, TechEmail, TechPhone;
TechName = request.getParameter("TechName");
TechUserName = request.getParameter("TechUserName");
TechPass = request.getParameter("TechPass");
TechPassVer = request.getParameter("TechPassVer");
TechRank = request.getParameter("TechRank");
TechSecQ = request.getParameter("TechSecQ");
TechSecA = request.getParameter("TechSecA");
TechEmail = request.getParameter("TechEmail");
TechPhone = request.getParameter("TechPhone");
if (TechName != null && TechUserName != null && TechPass != null
&& TechPassVer != null && TechRank != null
&& TechSecQ != null && TechSecA != null
&& TechEmail != null && TechPhone != null)
{
Technician t = new Technician(TechName, TechUserName, TechPass,
new ArrayList<Call>(), TechnicianRank.Beginner,
TechSecQ, TechSecA, TechPhone, TechEmail, (float) 0.0);
BackendFactory.getInstance().addTechnician(t);
}
%>
<body>
<h1>Adding Technican</h1>
<form name="tempForm" action="addTech.jsp" method="get">
<table align="left" border="0" cellpadding="1" cellspacing="1"
style="width: 500px;">
<tbody>
<tr>
<td><strong style="color: rgb(255, 0, 0);"><u>Tech
Details:</u></strong></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td>Id:</td>
<td><input name="TechId" readonly="readonly" type="text"
value=<%out.print(BackendFactory.getInstance().getTechnicianCurrentId());%> /></td>
</tr>
<tr>
<td> </td>
<td>Name:</td>
<td><input name="TechName" type="text" value="Your first name" /></td>
</tr>
<tr>
<td> </td>
<td>User name:</td>
<td><input name="TechUserName" type="text"
value="Your last name" /></td>
</tr>
<tr>
<td> </td>
<td>Password:</td>
<td><input name="TechPass" type="password" /></td>
</tr>
<tr>
<td> </td>
<td>Verify Password:</td>
<td><input name="TechPassVer" type="password" /></td>
</tr>
<tr>
<td> </td>
<td>Rank:</td>
<td><input name="TechRank" readonly="readonly" type="text"
value="Beginer" /></td>
</tr>
<tr>
<td> </td>
<td>Security Q:</td>
<td><input name="TechSecQ" size="30" type="text"
value="Whats your grandmother birth?" /></td>
</tr>
<tr>
<td> </td>
<td>Security A:</td>
<td><input name="TechSecA" size="30" type="text"
value="Dont remember..." /></td>
</tr>
<tr>
<td> </td>
<td>Email:</td>
<td><input name="TechEmail" type="text"
value="example@gmail.com" /></td>
</tr>
<tr>
<td> </td>
<td>Phone:</td>
<td><input name="TechPhone" type="text" value="0123456789" /></td>
</tr>
<tr>
<td> </td>
<td> </td>
<td><input name="addTech" type="submit" value="Submit" /></td>
</tr>
</tbody>
</table>
</form>
</body>
</html>
addCall.jsp：
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<%@page import="com.google.gwt.dom.client.SelectElement"%>
<%@page import="sun.reflect.CallerSensitive"%>
<%@page import="java.util.List"%>
<%@page import="java.util.ArrayList"%>
<html>
<%@page import="com.example.model.*"%>
<%@page import="com.example.backend.BackendFactory"%>
<%@page import="com.example.backend.ServerBackend"%>
<%@ page language="java" contentType="text/html; charset=windows-1255"
pageEncoding="windows-1255"%>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=windows-1255">
<title>Insert title here</title>
</head>
<body>
<h1>Adding Call
<%/*out.print(backend.findTechByName("sabag"));*/%>
</h1>
<form name="tempForm" action="addCall.jsp" method="get">
<%!ServerBackend backend = BackendFactory.getInstance();%>
<%
/*backend.addTechnician(new Technician());*/
//
String desc, tech, techRank, ClientAddress, ClientFirst, ClientLast;
desc = request.getParameter("desc");
tech = request.getParameter("tech");
ClientAddress = request.getParameter("ClientAddress");
ClientFirst = request.getParameter("ClientFirst");
ClientLast = request.getParameter("ClientLast");
Technician t=null ;
if (tech != null)
{
try
{
t=backend.findTechByName(tech);
} catch (Exception e)
{
t = new Technician();
t.setName(tech);
backend.addTechnician(t);
}
}
if (desc != null && tech != null && ClientAddress != null
&& ClientFirst != null && ClientLast != null)
{
Call call = new Call();
call.setDescription(desc);
call.setCaller(new Client(ClientFirst + ClientLast,
new Address(ClientAddress, ClientAddress,
ClientAddress, 45)));
call.setTechnician(t);
backend.addCall(call);
}
/**/
%>
<table align="left" border="0" cellpadding="1" cellspacing="1"
style="width: 500px;">
<tbody>
<tr>
<td><strong style="color: rgb(255, 0, 0);"><u>Call
Details:</u></strong></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td>Id:</td>
<td>
<div>
<input name="id" readonly="readonly" type="text"
value=<%out.print(backend.getCallCurrentId());%> />
</div>
</td>
</tr>
<tr>
<td> </td>
<td>Description:</td>
<td><textarea name="desc"></textarea></td>
</tr>
<tr>
<td> </td>
<td>Technician:</td>
<td><select name="tech" size="1">
<%
try
{
List<String> lst=backend.getAllTechsNames();
for(String s : lst) {
%>
<option value="100">
<%
out.print(s);
%>
</option>
<%
}
}
catch(Exception e)
{
%>
<option>
<%
out.println("fdghjk");
%>
</option>
<%
}
%>
</select> </td>
</tr>
<tr>
<td><strong><u><span
style="color: rgb(255, 0, 0);">Caller Details:</span></u></strong></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td>First name</td>
<td><input name="ClientFirst" type="text"
value="Your first name" /></td>
</tr>
<tr>
<td> </td>
<td>Last name</td>
<td><input name="ClientLast" type="text"
value="Your last name" /></td>
</tr>
<tr>
<td> </td>
<td>Address</td>
<td><input name="ClientAddress" type="text"
value="Your address" /></td>
</tr>
<tr>
<td> </td>
<td> </td>
<td><input name="addCall" type="submit" value="Submit" /></td>
</tr>
</tbody>
</table>
</form>
</body>
</html>
而且最重要的是： DBBackend代码：
package com.example.backend;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
import javax.persistence.TypedQuery;
import com.example.model.Call;
import com.example.model.CallStatus;
import com.example.model.SparePart;
import com.example.model.Technician;
import com.example.model.ThingToDo;
public class DBbackend implements Backend
{
private EntityManagerFactory emf = null;
private EntityManager em = null;
private String PERSISTENCE_UNIT_NAME = "transactions-optional";
//
public DBbackend()
{
emf = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
em = emf.createEntityManager();
}
private void insert(Object obj) throws Exception
{
em.getTransaction().begin();
em.persist(obj);
try
{
em.getTransaction().commit();
} catch (Exception e)
{
em.clear();
throw e;
}
}
@Override
public int getNextCallId()
{
// TODO Auto-generated method stub
return 0;
}
@Override
public void removeCall(int id) throws Exception
{
// TODO Auto-generated method stub
}
@Override
public ArrayList<Call> getCallsByTech(Technician t) throws Exception
{
// TODO Auto-generated method stub
return null;
}
@Override
public void updateCall(Call call) throws Exception
{
// TODO Auto-generated method stub
}
@Override
public void save()
{
// TODO Auto-generated method stub
}
@Override
public void addCall(Call call) throws Exception
{
// TODO Auto-generated method stub
}
@Override
public void addTechnician(Technician technician) throws Exception
{
// TODO Auto-generated method stub
insert(technician);
}
@Override
public Technician getTechnicianByUserName(String userName) throws Exception
{
// TODO Auto-generated method stub
return null;
}
@Override
public Call getCall(int id) throws Exception
{
// TODO Auto-generated method stub
return null;
}
@Override
public void addCallToTech(Call call, Technician t) throws Exception
{
// TODO Auto-generated method stub
call.setTechnician(t);
insert(call);
}
@Override
public Technician findTechByName(String name) throws Exception
{
// TODO Auto-generated method stub
Query q = em.createQuery(
"SELECT technician FROM Technician technician "
+ "WHERE technician.name = :Name ", Technician.class);
q.setParameter("Name", name);
return (Technician) q.getSingleResult();
}
@SuppressWarnings("unchecked")
@Override
public List<String> getAllTechsNames() throws Exception
{
// TODO Auto-generated method stub
TypedQuery<Technician> query =
em.createQuery("SELECT p FROM Technician p", Technician.class);
List<Technician> results = query.getResultList();
List<String> nameList = new ArrayList<String>();
for (Technician item : results)
nameList.add(item.getName());
return nameList;
}
@Override
public ArrayList<String> blabla() throws Exception
{
// TODO Auto-generated method stub
Query q = em.createQuery(
"SELECT technician FROM Technician technician",
Technician.class);
@SuppressWarnings("unchecked")
List<Technician> lst = q.getResultList();
ArrayList<String> nameList = new ArrayList<String>();
for (Technician item : lst)
nameList.add(item.getName());
return nameList;
}
@Override
public int getTechnicianCurrentId()
{
// TODO Auto-generated method stub
return Technician.getIdCount();
}
@Override
public int getCallCurrentId()
{
// TODO Auto-generated method stub
return Call.getIdCount();
}
}
堆栈跟踪：
来源：com.google.appengine.datanucleus.query.QueryEntityPKFetchFieldManager.fetchIntField（QueryEntityPKFetchFieldManager.java:70）类：com.google.appengine.datanucleus.query.QueryEntityPKFetchFieldManager方法：fetchIntField行：70Source：org.datanucleus.identity .IdentityUtils.getApplicationIdentityForResultSetRow（IdentityUtils.java:93）类：org.datanucleus.identity.IdentityUtils方法：getApplicationIdentityForResultSetRow行：93Source：com.google.appengine.datanucleus.EntityUtils.entityToPojo（EntityUtils.java:1011）类：com.google .appengine.datanucleus.EntityUtils方法：entityToPojo行：1011Source：com.google.appengine.datanucleus.query.DatastoreQuery $ 2.apply（DatastoreQuery.java:229）类：com.google.appengine.datanucleus.query.DatastoreQuery $ 2方法： apply Line：229Source：com.google.appengine.datanucleus.query.DatastoreQuery $ 2.apply（DatastoreQuery.java:226）类：com.google.appengine.datanucleus.query.DatastoreQuery $ 2方法：apply Line：226Source：com.goog le.appengine.datanucleus.query.LazyResult.resolveNext（LazyResult.java:96）类：com.google.appengine.datanucleus.query.LazyResult方法：resolveNext行：96Source：com.google.appengine.datanucleus.query.LazyResult。 resolveAll（LazyResult.java:121）类：com.google.appengine.datanucleus.query.LazyResult方法：resolveAll行：121Source：com.google.appengine.datanucleus.query.LazyResult.size（LazyResult.java:115）类： com.google.appengine.datanucleus.query.LazyResult方法：size行：115Source：com.google.appengine.datanucleus.query.StreamingQueryResult.size（StreamingQueryResult.java:151）类：com.google.appengine.datanucleus.query。 StreamingQueryResult方法：size行：151Source：org.datanucleus.store.query.AbstractQueryResult.toArray（AbstractQueryResult.java:400）类：org.datanucleus.store.query.AbstractQueryResult方法：toArray Line：400Source：java.util.ArrayList。 addAll（ArrayList.java:530）类：java.util.ArrayList方法：addAll Line：530Source：org.datanucleus.query。 evaluateator.JavaQueryEvaluator.execute（JavaQueryEvaluator.java:160）类：org.datanucleus.query.evaluator.JavaQueryEvaluator方法：执行Line：160Source：org.datanucleus.query.evaluator.JPQLEvaluator.execute（JPQLEvaluator.java:112）类： org.datanucleus.query.evaluator.JPQLEvaluator方法：执行Line：112Source：com.google.appengine.datanucleus.query.JPQLQuery.performExecute（JPQLQuery.java:200）类：com.google.appengine.datanucleus.query.JPQLQuery方法：performExecute Line：200Source：org.datanucleus.store.query.Query.executeQuery（Query.java:1789）类：org.datanucleus.store.query.Query方法：executeQuery Line：1789Source：org.datanucleus.store.query。 Query.executeWithMap（Query.java:1693）类：org.datanucleus.store.query.Query方法：executeWithMap行：1693Source：org.datanucleus.api.jpa.JPAQuery.getSingleResult（JPAQuery.java:232）类：org。 datanucleus.api.jpa.JPAQuery方法：getSingleResult行：232Source：com.example.backend.DBbackend.findTechByName（DBbackend.jav a：124）类：com.example.backend.DBbackend方法：findTechByName行：124Source：com.example.backend.ServerBackend.findTechByName（ServerBackend.java:101）类：com.example.backend.ServerBackend方法：findTechByName行： 101Source：org.apache.jsp.addCall_jsp._jspService（addCall_jsp.java:81）类：org.apache.jsp.addCall_jsp方法：_jspService行：81Source：org.apache.jasper.runtime.HttpJspBase.service（HttpJspBase.java： 97）类：org.apache.jasper.runtime.HttpJspBase方法：service行：97Source：javax.servlet.http.HttpServlet.service（HttpServlet.java:717）类：javax.servlet.http.HttpServlet方法：service line： 717Source：org.apache.jasper.servlet.JspServletWrapper.service（JspServletWrapper.java:377）类：org.apache.jasper.servlet.JspServletWrapper方法：service行：377Source：org.apache.jasper.servlet.JspServlet.serviceJspFile（ JspServlet.java:313）类：org.apache.jasper.servlet.JspServlet方法：serviceJspFile行：313Source：org.apache.jasper.servlet.JspServle t.service（JspServlet.java:260）类：org.apache.jasper.servlet.JspServlet方法：service行：260Source：com.google.appengine.tools.development.PrivilegedJspServlet.access $ 101（PrivilegedJspServlet.java:23）类：com.google.appengine.tools.development.PrivilegedJspServlet方法：访问$ 101行：23Source：com.google.appengine.tools.development.PrivilegedJspServlet $ 2.run（PrivilegedJspServlet.java:61）类：com.google.appengine.tools .development.PrivilegedJspServlet $ 2方法：run Line：61Source：java.security.AccessController.doPrivileged（Native Method）类：java.security.AccessController方法：doPrivileged Line：-2Source：com.google.appengine.tools.development.PrivilegedJspServlet。 service（PrivilegedJspServlet.java:58）类：com.google.appengine.tools.development.PrivilegedJspServlet方法：service行：58Source：javax.servlet.http.HttpServlet.service（HttpServlet.java:717）类：javax.servlet。 http.HttpServlet方法：service line：717Source：org.mortbay.jetty.servlet.Servlet Holder.handle（ServletHolder.java:511）类：org.mortbay.jetty.servlet.ServletHolder方法：handle行：511Source：org.mortbay.jetty.servlet.ServletHandler $ CachedChain.doFilter（ServletHandler.java:1166）类： org.mortbay.jetty.servlet.ServletHandler $ CachedChain方法：doFilter Line：1166Source：com.google.appengine.api.socket.dev.DevSocketFilter.doFilter（DevSocketFilter.java:74）类：com.google.appengine.api。 socket.dev.DevSocketFilter方法：doFilter行：74Source：org.mortbay.jetty.servlet.ServletHandler $ CachedChain.doFilter（ServletHandler.java:1157）类：org.mortbay.jetty.servlet.ServletHandler $ CachedChain方法：doFilter Line： 1157Source：com.google.appengine.tools.development.ResponseRewriterFilter.doFilter（ResponseRewriterFilter.java:123）类：com.google.appengine.tools.development.ResponseRewriterFilter方法：doFilter Line：123Source：org.mortbay.jetty.servlet。 ServletHandler $ CachedChain.doFilter（ServletHandler.java:1157）类：org.mortbay.jetty.servlet.ServletHand ler $ CachedChain方法：doFilter Line：1157Source：com.google.appengine.tools.development.HeaderVerificationFilter.doFilter（HeaderVerificationFilter.java:34）类：com.google.appengine.tools.development.HeaderVerificationFilter方法：doFilter Line：34Source： org.mortbay.jetty.servlet.ServletHandler $ CachedChain.doFilter（ServletHandler.java:1157）类：org.mortbay.jetty.servlet.ServletHandler $ CachedChain方法：doFilter Line：1157Source：com.google.appengine.api.blobstore。 dev.ServeBlobFilter.doFilter（ServeBlobFilter.java:63）类：com.google.appengine.api.blobstore.dev.ServeBlobFilter方法：doFilter行：63Source：org.mortbay.jetty.servlet.ServletHandler $ CachedChain.doFilter（ServletHandler。 java：1157）类：org.mortbay.jetty.servlet.ServletHandler $ CachedChain方法：doFilter行：1157Source：com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter（TransactionCleanupFilter.java:43）类：com.google。 apphosting.utils.servlet.TransactionCleanupFilter方法：doFilter行：43Source：org.mortbay.jetty.servlet.ServletHandler $ CachedChain.doFilter（ServletHandler.java:1157）类：org.mortbay.jetty.servlet.ServletHandler $ CachedChain方法：doFilter Line：1157Source：com.google.appengine。 tools.development.StaticFileFilter.doFilter（StaticFileFilter.java:125）类：com.google.appengine.tools.development.StaticFileFilter方法：doFilter行：125Source：org.mortbay.jetty.servlet.ServletHandler $ CachedChain.doFilter（ServletHandler。 java：1157）类：org.mortbay.jetty.servlet.ServletHandler $ CachedChain方法：doFilter行：1157Source：com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest（DevAppServerModulesFilter.java:368）类：com.google。 appengine.tools.development.DevAppServerModulesFilter方法：doDirectRequest行：368Source：com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest（DevAppServerModulesFilter.java:351）类：com.google.appengine.tools.development.DevAppServerModulesFilter Met hod：doDirectModuleRequest行：351Source：com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter（DevAppServerModulesFilter.java:116）类：com.google.appengine.tools.development.DevAppServerModulesFilter方法：doFilter行：116Source：org.mortbay .jetty.servlet.ServletHandler $ CachedChain.doFilter（ServletHandler.java:1157）类：org.mortbay.jetty.servlet.ServletHandler $ CachedChain方法：doFilter行：1157Source：org.mortbay.jetty.servlet.ServletHandler.handle（ServletHandler .java：388）类：org.mortbay.jetty.servlet.ServletHandler方法：handle Line：388Source：org.mortbay.jetty.security.SecurityHandler.handle（SecurityHandler.java:216）类：org.mortbay.jetty.security .SecurityHandler方法：handle Line：216Source：org.mortbay.jetty.servlet.SessionHandler.handle（SessionHandler.java:182）类：org.mortbay.jetty.servlet.SessionHandler方法：handle Line：182Source：org.mortbay.jetty .handler.ContextHandler.handle（ContextHandler.java:765）类：org.mortbay.j etty.handler.ContextHandler方法：handle Line：765Source：org.mortbay.jetty.webapp.WebAppContext.handle（WebAppContext.java:418）类：org.mortbay.jetty.webapp.WebAppContext方法：handle Line：418Source：com。 google.appengine.tools.development.DevAppEngineWebAppContext.handle（DevAppEngineWebAppContext.java:97）类：com.google.appengine.tools.development.DevAppEngineWebAppContext方法：handle Line：97Source：org.mortbay.jetty.handler.HandlerWrapper.handle（ HandlerWrapper.java:152）类：org.mortbay.jetty.handler.HandlerWrapper方法：handle Line：152Source：com.google.appengine.tools.development.JettyContainerService $ ApiProxyHandler.handle（JettyContainerService.java:485）Class：com。 google.appengine.tools.development.JettyContainerService $ ApiProxyHandler方法：handle Line：485Source：org.mortbay.jetty.handler.HandlerWrapper.handle（HandlerWrapper.java:152）类：org.mortbay.jetty.handler.HandlerWrapper方法：handle行：152Source：org.mortbay.jetty.Server.handle（Server.java： 326）类：org.mortbay.jetty.Server方法：handle行：326Source：org.mortbay.jetty.HttpConnection.handleRequest（HttpConnection.java:542）类：org.mortbay.jetty.HttpConnection方法：handleRequest行：542Source： org.mortbay.jetty.HttpConnection $ RequestHandler.headerComplete（HttpConnection.java:923）类：org.mortbay.jetty.HttpConnection $ RequestHandler方法：headerComplete行：923Source：org.mortbay.jetty.HttpParser.parseNext（HttpParser.java： 547）类：org.mortbay.jetty.HttpParser方法：parseNext行：547Source：org.mortbay.jetty.HttpParser.parseAvailable（HttpParser.java:212）类：org.mortbay.jetty.HttpParser方法：parseAvailable行：212Source： org.mortbay.jetty.HttpConnection.handle（HttpConnection.java:404）类：org.mortbay.jetty.HttpConnection方法：handle Line：404Source：org.mortbay.io.nio.SelectChannelEndPoint.run（SelectChannelEndPoint.java:409）类：org.mortbay.io.nio.SelectChannelEndPoint方法：运行Line：409Source：org.mortbay.thread.QueuedThreadPoo l $ PoolThread.run（QueuedThreadPool.java:582）类：org.mortbay.thread.QueuedThreadPool $ PoolThread方法：运行Line：582}
我无法从em中选择任何内容!!!
答案 0 :(得分：0)
只是一个提示，当你有一个可以为null的变量时，使用它作为参数，而不是调用方法。
如果你使用。在变量为null之后的运算符，您将获得null异常。例如：
if( variable_could_be_null.equals(variable_known_to_not_be_null) )
最终会在某些时候给你一个null异常。但这不会：
if( variable_known_to_not_be_null.equals(variable_could_be_null) )
因为在这里你总是使用。定义了您知道的变量的运算符。
在使用可能为null的值之前，请检查它：
if(variable_could_be_null!=null)
{
...
}