Question

我正在创建一个使用hibernate和spring mvc从db读取数据的网格库..我有2个表employee，它有EPMID，EMPNAME，EMPAGE，SALARY，ADDRESS，department_id（引用于department_id in部门表）和department，其中有department_id和名称......这里是Department.java

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;}

以及在服务中添加员工的功能

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);

没有那行employee.getDepartment().setDepId(Integer.parseInt(list[3]));，一切都很顺利，但我想在主要的一行上添加外键来引用.. 这是例外

＆＃13;

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
	at com.dineshonjava.service.EmployeeServiceImpl.addEmployee(EmployeeServiceImpl.java:27)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
	at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:266)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
	at com.sun.proxy.$Proxy30.addEmployee(Unknown Source)
	at com.dineshonjava.controller.EmployeeController.doPostSave(EmployeeController.java:65)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:781)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:721)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

＆＃13;

Answer 1

不使用类似

之类的内容维护外键

ambhas

取而代之的是

employee.getDepartment().setDepId(Integer.parseInt(list[3]));

Hibernate现在通过在employee表中插入department_id来创建部门和员工之间的数据库关系。

P.S。我假设一些类和方法名称，因为我没有你的所有代码。

关于NPE

我相信您收到了空指针异常，因为员工当时没有部门。

Department dept = departmentDao.findById(Integer.parseInt(list[3]));
employee.setDepartment(dept);

将外键添加到数据库中

1 个答案: