持久时，EntityManager返回NullPointerException [英] EntityManager returns NullPointerException when persisting
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问题描述
当我坚持使用 Joueur（参见下面的类）时，会收到NullPointerException，但我不知道为什么
When I persist a "Joueur" (cf my class below), I get a NullPointerException, but I don't know why
em.persist(new Joueur("pseudo", "mdp", "mail"));
这是我的课程 Joueur：
This is my class "Joueur" :
@Entity
@NamedQueries({
@NamedQuery(name = "trouverParMail", query = "SELECT * FROM Joueur j WHERE j.mail = :mail")})
public class Joueur implements Serializable {
private static final long serialVersionUID = 1L;
private String pseudo;
private String mdp;
private String mail;
private Integer nbParties;
private Integer nbPartiesGagnees;
public Joueur() {
}
public Joueur(String pseudo, String mdp, String mail)
{
this.pseudo = pseudo;
this.mdp = mdp;
this.mail = mail;
this.nbParties = 0;
this.nbPartiesGagnees = 0;
}
@Id
public String getPseudo()
{
return pseudo;
}
public String getMdp()
{
return mdp;
}
public String getMail()
{
return mail;
}
public Integer getNbParties()
{
return nbParties;
}
public Integer getNbPartieGagnees()
{
return nbPartiesGagnees;
}
public void setPseudo(String pseudo) {
this.pseudo = pseudo;
}
public void setMdp(String mdp) {
this.mdp = mdp;
}
public void setMail(String mail) {
this.mail = mail;
}
public void setNbParties(Integer nbParties)
{
this.nbParties = nbParties;
}
public void setNbPartiesGagnees(Integer nbPartiesGagnees)
{
this.nbPartiesGagnees = nbPartiesGagnees;
}
}
和错误堆栈：
java.lang.NullPointerException
at login.LoginBean.inscription(LoginBean.java:46)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1052)
at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1124)
at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:5388)
at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:619)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:571)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doAround(SystemInterceptorProxy.java:162)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:144)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:861)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800)
at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:370)
at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:5360)
at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:5348)
at com.sun.ejb.containers.EJBObjectInvocationHandler.invoke(EJBObjectInvocationHandler.java:206)
at com.sun.ejb.containers.EJBObjectInvocationHandlerDelegate.invoke(EJBObjectInvocationHandlerDelegate.java:79)
at $Proxy255.inscription(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.sun.corba.ee.impl.presentation.rmi.StubInvocationHandlerImpl.privateInvoke(StubInvocationHandlerImpl.java:241)
at com.sun.corba.ee.impl.presentation.rmi.StubInvocationHandlerImpl.invoke(StubInvocationHandlerImpl.java:152)
at com.sun.corba.ee.impl.presentation.rmi.codegen.CodegenStubBase.invoke(CodegenStubBase.java:227)
at login.__LoginRemote_Remote_DynamicStub.inscription(login/__LoginRemote_Remote_DynamicStub.java)
at login._LoginRemote_Wrapper.inscription(login/_LoginRemote_Wrapper.java)
at org.apache.jsp.inscription_jsp._jspService(inscription_jsp.java from :95)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:770)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:403)
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:770)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1542)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:849)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:746)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1045)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:228)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:680)
您知道错误在哪里吗？ Tkx
Do you know where is the error ? Tkx
推荐答案
根据您给出的描述，NullPointerException的来源在此行中：
According description you gave, origin of NullPointerException is in this line:
em.persist(new Joueur("pseudo", "mdp", "mail"));
唯一可能的原因是em为空。可能为null的原因是LoginBean无法注入EntityManager。如果是这样，也许LoginBean不是容器管理的组件？也许您忘记了@Stateless注释？
Only possible cause is that em is null. Likely reason for it being null is that LoginBean failed to inject EntityManager. If so, maybe LoginBean is not container managed component? Maybe you forgot @Stateless annotation?
如果这没有回答您的问题，则必须分享更多详细信息：
If this didn't answered to your question, you have to share more details:
- 如何获取对实体管理器的引用？
- 它在其他类中是否起作用？
- LoginBean的代码如何？ ？
这篇关于持久时，EntityManager返回NullPointerException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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