使用Hibernate Spring的.getCurrentSession（）之后出错

Question

使用.getCurrentSession（）获取Session时收到以下错误。

错误 ：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'miniVLEController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: miniVLE.service.StudentService miniVLE.controller.miniVLEController.studentService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'studentService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: miniVLE.dao.MiniVLEDAOImplementation miniVLE.service.StudentService.dao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'miniVLEDAOImplementation' defined in file [C:\\Users\\1\\Documents\\NetBeansProjects\\com3014_mini_VLE\\build\\web\\WEB-INF\\classes\\miniVLE\\dao\\MiniVLEDAOImplementation.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [miniVLE.dao.MiniVLEDAOImplementation]: Constructor threw exception; nested exception is java.lang.NullPointerException

DAO实施：

import java.util.ArrayList;
import java.util.List;
import miniVLE.beans.Course;
import miniVLE.beans.Department;
import miniVLE.beans.Module;
import miniVLE.beans.Student;
import miniVLE.beans.TimeSlot;
import org.hibernate.SessionFactory;
import org.hibernate.criterion.Restrictions;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

@Repository
public class MiniVLEDAOImplementation implements MiniVLEDAO{

    // Used for communicating with the database
    @Autowired
    private SessionFactory sessionFactory;

    /**
     * DAO constructor filled with dummy data 
     */
    public MiniVLEDAOImplementation() {
        System.out.println("*** MiniVLEDAOImplementation instantiated");
        Student s1 = new Student("123456","Bob","123");
        Department d1 = new Department("COM","Computing");
        Course c1 = new Course("COM3014","Web");
        c1.setDepartment(d1);
        s1.setCourse(c1);
        s1.setDept(d1);

        // Add new student to the database
        addStudentToDB(s1);

    }

    /**
     * Gets the current session and adds new student row into the database
     * @param student 
     */
    @Override
    public void addStudentToDB(Student student) {         
        sessionFactory.getCurrentSession();  // here i got rid of full implementation as it fails on getting the current session
    } ... 

调度员小服务程序：

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
       http://www.springframework.org/schema/aop 
       http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
       http://www.springframework.org/schema/tx 
       http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context-3.0.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd">

    <context:annotation-config />
    <context:component-scan base-package="miniVLE.controller" />
    <context:component-scan base-package="miniVLE.service" />
    <context:component-scan base-package="miniVLE.beans" />
    <context:component-scan base-package="miniVLE.dao" />

    <!-- Declare a view resolver-->
    <bean id="viewResolver"
          class="org.springframework.web.servlet.view.InternalResourceViewResolver"
          p:prefix="/WEB-INF/jsp/"
          p:suffix=".jsp" />


    <!-- Connects to the database based on the jdbc properties information-->
    <bean id="dataSource" class ="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name ="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name ="url" value="jdbc:derby://localhost:1527/minivledb"/>
        <property name ="username" value="root"/>
        <property name ="password" value="123" />
    </bean>

     <!-- Declares hibernate object -->
    <bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect"> ${hibernate.dialect}</prop>
                <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>
            </props>
        </property>
        <!-- A list of all the annotated bean files, which are mapped with database tables-->
        <property name="annotatedClasses">
            <list>
                <value> miniVLE.beans.Course </value>
                <value> miniVLE.beans.Student </value>
                <value> miniVLE.beans.Department </value>  
                <value> miniVLE.beans.Module </value>  
                <value> miniVLE.beans.TimeSlot </value> 
            </list>
        </property>
    </bean>

</beans>

Answer 1

要创建bean，Spring首先使用类的无参构造函数来创建实例，然后使用反射来自动装配@Autowired字段。

但是你的构造函数

public MiniVLEDAOImplementation() {
    ...
    // Add new student to the database
    addStudentToDB(s1);
}

在初始化之前调用使用SessionFactory的方法。 因此它为null并且在尝试调用方法时会出现NullPointerException 。

您无法从该点将学生添加到数据库。 如果您想测试您的课程，请尝试单元测试。