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球員我正在做一個網格庫，使用休眠和彈簧mvc從數據庫讀取數據..我有2表employee其中有EPMID，EMPNAME，EMPAGE，SALARY，ADDRESS，department_id（refrences to在部門表部門標識），並department已部門標識和名稱...這裏是Department.java將外鍵添加到數據庫
public class Department {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "department_id")
private int depId;
@Column(name = "name")
private String depName;
@OneToMany(mappedBy="department",cascade = { CascadeType.ALL }, orphanRemoval=true)
private List<Employee> employees;}
Employee.java
public class Employee {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "EMPID")
private int empId;
@Column(name = "EMPNAME")
private String empName;
@Column(name = "ADDRESS")
private String empAddress;
@Column(name = "SALARY")
private String salary;
@Column(name = "EMPAGE")
private int empAge;
@ManyToOne(cascade={CascadeType.ALL})
@JoinColumn(name="department_id")
private Department department;}
，並且增加了格蘭員工在服務
01功能public void addEmployee(String[] list, Employee employee) {
employee.getDepartment().setDepId(Integer.parseInt(list[3]));
employee.setEmpName(list[2]);
employee.setEmpAge(Integer.parseInt(list[4]));
employee.setEmpAddress(list[6]);
employee.setSalary(list[1]);
this.employeeDao.addOrEditEmployee(employee);
一切順利，而不該行employee.getDepartment().setDepId(Integer.parseInt(list[3]));但我想補充外鍵上小學一參考.. 這裏是例外
SEVERE: Servlet.service() for servlet [sdnext] in context with path [/Spring3HibernateApp1] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
\t at com.dineshonjava.service.EmployeeServiceImpl.addEmployee(EmployeeServiceImpl.java:27)
\t at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
\t at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
\t at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
\t at java.lang.reflect.Method.invoke(Unknown Source)
\t at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
\t at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
\t at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
\t at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
\t at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:266)
\t at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
\t at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
\t at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
\t at com.sun.proxy.$Proxy30.addEmployee(Unknown Source)
\t at com.dineshonjava.controller.EmployeeController.doPostSave(EmployeeController.java:65)
\t at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
\t at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
\t at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
\t at java.lang.reflect.Method.invoke(Unknown Source)
\t at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
\t at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
\t at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
\t at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:781)
\t at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:721)
\t at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
\t at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
\t at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
\t at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
\t at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
\t at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
\t at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
\t at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
\t at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
\t at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
\t at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
\t at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
\t at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
\t at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
\t at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
\t at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
\t at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
\t at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
\t at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
\t at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
\t at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
\t at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
\t at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
\t at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
\t at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
\t at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
\t at java.lang.Thread.run(Unknown Source)