Question

我收到空指针异常。我不确定如何处理泛型类：

Servlet.service() for servlet [LogServlet] in context with path [/CompanyProject] threw exceptionjava.lang.NullPointerException
at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.<init>(SessionImpl.java:2544)
at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.<init>(SessionImpl.java:2531)
at org.hibernate.internal.SessionImpl.byId(SessionImpl.java:1079)
at org.hibernate.internal.SessionImpl.get(SessionImpl.java:991)
at com.myproject.dao.MainDao.findById(MainDao.java:26)
at com.myproject.controller.LoginFilter.doFilter(LoginFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

这是主要的代码构造：

public MainDao() {
    session=(new Configuration().configure()).buildSessionFactory().openSession();
}

方法：

public T findById(String i){
    session.beginTransaction();
    T obj= (T) session.get(managedClass,(Serializable) i);
    session.getTransaction().commit();
    return obj;
}

想法？

Answer 1

由于某种原因，我只需要再次构建路径以包含hibernate jar。

Hibernate Maven项目按ID查找实体

1 个答案: