「HTTP狀態500-Servlet.init（）爲servlet彈出異常」

Question

您好我正在嘗試使用Hibernate和Postgresql的簡單Spring MVC CRUD應用程序。我得到的例外是下面

EXCEPTOIN：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.service.EmployeeService com.controller.EmployeeController.employeeService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.dao.EmployeeDao com.serviceImpl.EmployeeServiceImpl.employeeDao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.daoImp.EmployeeDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException 
    org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:287) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456) 
    org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294) 
    org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225) 

org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.service.EmployeeService com.controller.EmployeeController.employeeService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.dao.EmployeeDao bean class [com.daoImp.EmployeeDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException 
    org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:506) 
    org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87) 
    org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:284) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456) 
    org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294) 
    org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225) 
    org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291) 
    org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193) 

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.dao.EmployeeDao com.serviceImpl.EmployeeServiceImpl.employeeDao; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.daoImp.EmployeeDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException 
    org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:287) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517) 
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456) 
    org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294) 
    org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225) 
    org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291) 

org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.dao.EmployeeDao com.serviceImpl.EmployeeServiceImpl.employeeDao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeDao' defined in file [/Users/mohammad.waseem/Downloads/apache-tomcat-8.5.6/webapps/crud/WEB-INF/classes/com/daoImp/EmployeeDaoImpl.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.daoImp.EmployeeDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException 
    org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:506) 

pom.xml文件

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> 
    <modelVersion>4.0.0</modelVersion> 
    <groupId>com</groupId> 
    <artifactId>crud</artifactId> 
    <packaging>war</packaging> 
    <version>1.0.0-SNAPSHOT</version> 
    <name>crud Maven Webapp</name> 
    <url>http://maven.apache.org</url> 
    <properties> 
     <org.springframework.version>3.1.1.RELEASE</org.springframework.version> 
    </properties> 

     <dependencies> 
      <dependency> 
       <groupId>junit</groupId> 
       <artifactId>junit</artifactId> 
       <version>3.8.1</version> 
       <scope>test</scope> 
      </dependency> 


      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-core</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-expression</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-beans</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-aop</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-context</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-context-support</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-tx</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-jdbc</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-orm</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-oxm</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-web</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-webmvc</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-webmvc-portlet</artifactId> 
       <version>${org.springframework.version}</version> 
      </dependency> 
      <dependency> 
       <groupId>javax.servlet</groupId> 
       <artifactId>jstl</artifactId> 
       <version>1.2</version> 
      </dependency> 

      <dependency> 
       <groupId>org.springframework</groupId> 
       <artifactId>spring-test</artifactId> 
       <version>${org.springframework.version}</version> 
       <scope>test</scope> 
      </dependency> 

      <dependency> 
       <groupId>org.postgresql</groupId> 
       <artifactId>postgresql</artifactId> 
       <version>9.4-1206-jdbc42</version> 
      </dependency> 
      <dependency> 
       <groupId>commons-dbcp</groupId> 
       <artifactId>commons-dbcp</artifactId> 
       <version>1.2.2</version> 
      </dependency> 
      <dependency> 
       <groupId>commons-pool</groupId> 
       <artifactId>commons-pool</artifactId> 
       <version>1.6</version> 
      </dependency> 
      <dependency> 
       <groupId>org.hibernate</groupId> 
       <artifactId>hibernate-core</artifactId> 
       <version>4.0.1.Final</version> 
      </dependency> 
      <dependency> 
       <groupId>org.hibernate</groupId> 
       <artifactId>hibernate-validator</artifactId> 
       <version>4.2.0.Final</version> 
      </dependency> 
      <dependency> 
       <groupId>org.hibernate.common</groupId> 
       <artifactId>hibernate-commons-annotations</artifactId> 
       <version>4.0.1.Final</version> 
       <classifier>tests</classifier> 
      </dependency> 
      <dependency> 
       <groupId>org.hibernate.javax.persistence</groupId> 
       <artifactId>hibernate-jpa-2.0-api</artifactId> 
       <version>1.0.1.Final</version> 
      </dependency> 
      <dependency> 
       <groupId>org.hibernate</groupId> 
       <artifactId>hibernate-entitymanager</artifactId> 
       <version>4.0.1.Final</version> 
      </dependency> 
      <dependency> 
       <groupId>javax.validation</groupId> 
       <artifactId>validation-api</artifactId> 
       <version>1.0.0.GA</version> 
       <scope>provided</scope> 
      </dependency> 
      <dependency> 
       <groupId>org.slf4j</groupId> 
       <artifactId>slf4j-api</artifactId> 
       <version>1.6.4</version> 
      </dependency> 
      <dependency> 
       <groupId>org.jboss.logging</groupId> 
       <artifactId>jboss-logging</artifactId> 
       <version>3.1.0.CR2</version> 
      </dependency> 
      <dependency> 
       <groupId>org.slf4j</groupId> 
       <artifactId>slf4j-log4j12</artifactId> 
       <version>1.6.4</version> 
      </dependency> 
     </dependencies> 
     <build> 
      <finalName>crud</finalName> 
     </build> 
    </project> 

在WEB-INF

web.xml文件

<?xml version="1.0" encoding="UTF-8"?> 
<web-app 
     xmlns="http://java.sun.com/xml/ns/javaee" 
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
     http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
     version="3.0"> 
    <servlet> 
     <servlet-name>spring</servlet-name> 
     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> 
     <load-on-startup>1</load-on-startup> 
    </servlet> 
    <servlet-mapping> 
     <servlet-name>spring</servlet-name> 
     <url-pattern>/</url-pattern> 
    </servlet-mapping> 
</web-app> 

彈簧-servlet.xml文件

 <beans xmlns:context="http://www.springframework.org/schema/context" 
      xmlns:tx="http://www.springframework.org/schema/tx" 
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xmlns="http://www.springframework.org/schema/beans" 
      xsi:schemaLocation=" 

    http://www.springframework.org/schema/beans 

    http://www.springframework.org/schema/beans/spring-beans-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/tx 

    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"> 

     <context:component-scan base-package="com"></context:component-scan> 
     <tx:annotation-driven transaction-manager="hibernateTransactionManager"></tx:annotation-driven> 
     <bean id="viewResolver" 

class="org.springframework.web.servlet.view.InternalResourceViewResolver"> 
      <property name="viewClass" 

value="org.springframework.web.servlet.view.JstlView"></property> 
      <property name="prefix" value="/WEB-INF/jsp/"></property> 
      <property name="suffix" value=".jsp"></property> 
     </bean> 

     <bean class="org.springframework.jdbc.datasource.DriverManagerDataSource" id="dataSource"> 

      <property name="driverClassName" value="org.postgresql.Driver"></property> 

      <property name="url" value="jdbc:postgresql://localhost:5433/databasedb"></property> 
      <property name="username" value="postgres"></property> 
      <property name="password" value="password"></property> 
     </bean> 

     <bean class="org.springframework.orm.hibernate4.LocalSessionFactoryBean" id="sessionFactory"> 

      <property name="dataSource" ref="dataSource"></property> 
      <property name="annotatedClasses"> 

       <list> 
        <value>com.model.Employee</value> 
       </list> 

      </property> 
      <property name="hibernateProperties"> 
       <props> 

        <prop key="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</prop> 
        <prop key="hibernate.hbm2ddl.auto">update</prop> 
        <prop key="hibernate.show_sql">true</prop> 
        <prop key="hibernate.current_session_context_class">thread</prop> 
       </props> 

      </property> 

     </bean> 

     <bean class="org.springframework.orm.hibernate4.HibernateTransactionManager" id="hibernateTransactionManager"> 

      <property name="sessionFactory" ref="sessionFactory"></property> 

     </bean> 

    </beans> 

引用EmployeeBean類下com.bean包

package com.bean; 

/** 
* Created by mohammad.waseem on 21/11/16. 
*/ 
public class EmployeeBean { 
    private Integer id; 
    private String name; 
    private Integer age; 
    private Long salary; 
    private String address; 

    public EmployeeBean() { 
    } 

    public Integer getId() { 
     return id; 
    } 

    public void setId(Integer id) { 
     this.id = id; 
    } 

    public String getName() { 
     return name; 
    } 

    public void setName(String name) { 
     this.name = name; 
    } 

    public Integer getAge() { 
     return age; 
    } 

    public void setAge(Integer age) { 
     this.age = age; 
    } 

    public Long getSalary() { 
     return salary; 
    } 

    public void setSalary(Long salary) { 
     this.salary = salary; 
    } 

    public String getAddress() { 
     return address; 
    } 

    public void setAddress(String address) { 
     this.address = address; 
    } 
} 

EmployeeController類下com.controller

package com.controller; 

import com.bean.EmployeeBean; 
import com.model.Employee; 
import com.service.EmployeeService; 
import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.stereotype.Controller; 
import org.springframework.validation.BindingResult; 
import org.springframework.web.bind.annotation.ModelAttribute; 
import org.springframework.web.bind.annotation.RequestMapping; 
import org.springframework.web.bind.annotation.RequestMethod; 
import org.springframework.web.servlet.ModelAndView; 

import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.List; 
import java.util.Map; 

/** 
* Created by mohammad.waseem on 21/11/16. 
*/ 
@Controller 
public class EmployeeController { 
    @Autowired 
    private EmployeeService employeeService; 

    @RequestMapping(value = "/save", method = RequestMethod.POST) 
    public ModelAndView saveEmployee(@ModelAttribute("command") EmployeeBean employeeBean, BindingResult result) { 
     Employee employee = prepareModel(employeeBean); 
     employeeService.addEmployee(employee); 
     return new ModelAndView("redirect:/add.html"); 
    } 

    @RequestMapping(value = "/employees", method = RequestMethod.GET) 
    public ModelAndView listEmployees() { 
     Map<String, Object> map = new HashMap<String, Object>(); 
     map.put("employees", prepareListtoBean(employeeService.listEmployeess())); 
     return new ModelAndView("employeeList", map); 
    } 

    @RequestMapping(value = "/add", method = RequestMethod.GET) 
    public ModelAndView addEmployee(@ModelAttribute("command") EmployeeBean employeeBean, BindingResult result) { 
     Map<String, Object> map = new HashMap<String, Object>(); 
     map.put("employees", prepareListtoBean(employeeService.listEmployeess())); 
     return new ModelAndView("addEmployee", map); 
    } 

    @RequestMapping(value = "/index", method = RequestMethod.GET) 
    public ModelAndView welcome() { 
     return new ModelAndView("index"); 
    } 

    @RequestMapping(value = "/delete", method = RequestMethod.GET) 
    public ModelAndView editEmployee(@ModelAttribute("command") EmployeeBean employeeBean, BindingResult result) { 
     employeeService.deleteEmployee(prepareModel(employeeBean)); 
     Map<String, Object> map = new HashMap<String, Object>(); 
     map.put("employee", null); 
     map.put("employees", prepareListtoBean(employeeService.listEmployeess())); 
     return new ModelAndView("addEmployee", map); 
    } 

    @RequestMapping(value = "/edit", method = RequestMethod.GET) 
    public ModelAndView deleteEmployee(@ModelAttribute("command") EmployeeBean employeeBean, BindingResult result) { 
     Map<String, Object> map = new HashMap<String, Object>(); 
     map.put("employee", prepareEmployeeBean(employeeService.getEmployee(employeeBean.getId()))); 
     map.put("Employees", prepareListtoBean(employeeService.listEmployeess())); 
     return new ModelAndView("addEmployee", map); 
    } 

    private Employee prepareModel(EmployeeBean employeeBean) { 
     Employee employee = new Employee(); 
     employee.setEmpAddress(employeeBean.getAddress()); 
     employee.setEmpAge(employeeBean.getAge()); 
     employee.setEmpName(employeeBean.getName()); 
     employee.setSalary(employeeBean.getSalary()); 
     employee.setEmpId(employeeBean.getId()); 
     employeeBean.setId(null); 
     return employee; 

    } 

    private List<EmployeeBean> prepareListtoBean(List<Employee> employees) { 
     List<EmployeeBean> employeeBeanList = null; 
     if (employees != null && !employees.isEmpty()) { 
      employeeBeanList = new ArrayList<EmployeeBean>(); 
      EmployeeBean employeeBean = null; 
      for (Employee employee : employees) { 
       employeeBean = new EmployeeBean(); 
       employeeBean.setName(employee.getEmpName()); 
       employeeBean.setSalary(employee.getSalary()); 
       employeeBean.setAddress(employee.getEmpAddress()); 
       employeeBean.setAge(employee.getEmpAge()); 
       employeeBean.setId(employee.getEmpId()); 
       employeeBeanList.add(employeeBean); 
      } 
     } 
     return employeeBeanList; 
    } 

    private EmployeeBean prepareEmployeeBean(Employee employee) { 
     EmployeeBean employeeBean = new EmployeeBean(); 
     employeeBean.setAddress(employee.getEmpAddress()); 
     employeeBean.setAge(employee.getEmpAge()); 
     employeeBean.setName(employee.getEmpName()); 
     employeeBean.setSalary(employee.getSalary()); 
     employeeBean.setId(employee.getEmpId()); 
     return employeeBean; 
    } 
} 

com.dao包下的EmployeeDao類

package com.dao;

package com.daoImp; 

import com.dao.EmployeeDao; 
import com.model.Employee; 
import org.hibernate.SessionFactory; 
import org.hibernate.Transaction; 
import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.stereotype.Repository; 

import java.util.List; 

/** 
* Created by mohammad.waseem on 21/11/16. 
*/ 
@Repository("employeeDao") 
public class EmployeeDaoImpl implements EmployeeDao { 
    @Autowired 
    private SessionFactory sessionFactory; 

    Transaction tx = sessionFactory.getCurrentSession().beginTransaction(); 


    public void addEmployee(Employee employee) { 
     sessionFactory.getCurrentSession().saveOrUpdate(employee); 
    } 

    @SuppressWarnings("unchecked") 
    public List<Employee> listEmployeess() { 
     tx.commit(); 

     return (List<Employee>) sessionFactory.getCurrentSession().createCriteria(Employee.class).list(); 

    } 

    public Employee getEmployee(int empid) { 
     return (Employee) sessionFactory.getCurrentSession().get(Employee.class, empid); 
    } 

    public void deleteEmployee(Employee employee) { 
     sessionFactory.getCurrentSession().createQuery("Delete from Employee where empid=" + employee.getEmpId()).executeUpdate(); 
    } 
} 

Employee類下com.model com.daoImp

下

import com.model.Employee; 

import java.util.List; 

/** 
* Created by mohammad.waseem on 21/11/16. 
*/ 
public interface EmployeeDao{ 
    public void addEmployee(Employee employee); 
    public List<Employee> listEmployeess(); 
    public Employee getEmployee(int empid); 
    public void deleteEmployee(Employee employee); 
} 

EmployeeDaoImpl類

package com.model; 

import javax.persistence.*; 
import java.io.Serializable; 

/** 
* Created by mohammad.waseem on 21/11/16. 
*/ 
@Entity 
@Table(name = "EMPLOYEE") 
public class Employee implements Serializable{ 
    @Id 
    @GeneratedValue(strategy = GenerationType.AUTO) 
    @Column(name = "empid") 
    private Integer empId; 
    @Column(name = "empname") 
    private String empName; 
    @Column(name = "empaddress") 
    private String empAddress; 
    @Column(name = "salary") 
    private Long salary; 
    @Column(name = "empAge") 
    private Integer empAge; 

    public Integer getEmpId() { 
     return empId; 
    } 

    public void setEmpId(Integer empId) { 
     this.empId = empId; 
    } 

    public String getEmpName() { 
     return empName; 
    } 

    public void setEmpName(String empName) { 
     this.empName = empName; 
    } 

    public String getEmpAddress() { 
     return empAddress; 
    } 

    public void setEmpAddress(String empAddress) { 
     this.empAddress = empAddress; 
    } 

    public Long getSalary() { 
     return salary; 
    } 

    public void setSalary(Long salary) { 
     this.salary = salary; 
    } 

    public Integer getEmpAge() { 
     return empAge; 
    } 

    public void setEmpAge(Integer empAge) { 
     this.empAge = empAge; 
    } 
} 

的EmployeeService接口下com.service包

package com.service; 

import com.model.Employee; 

import java.util.List; 

/** 
* Created by mohammad.waseem on 21/11/16. 
*/ 
public interface EmployeeService { 
    public void addEmployee(Employee employee); 
    public List<Employee> listEmployeess(); 
    public Employee getEmployee(int empid); 
    public void deleteEmployee(Employee employee); 
} 

EmployeeServiceIm pl class under com。serviceImpl

package com.serviceImpl; 

import com.dao.EmployeeDao; 
import com.model.Employee; 
import com.service.EmployeeService; 
import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.stereotype.Service; 
import org.springframework.transaction.annotation.Propagation; 
import org.springframework.transaction.annotation.Transactional; 

import java.util.List; 

/** 
* Created by mohammad.waseem on 21/11/16. 
*/ 
@Service("employeeService") 
@Transactional(propagation = Propagation.SUPPORTS,readOnly = true) 
public class EmployeeServiceImpl implements EmployeeService { 
    @Autowired 
    private EmployeeDao employeeDao; 
    @Transactional(propagation = Propagation.REQUIRED,readOnly = false) 
    public void addEmployee(Employee employee) { 
     employeeDao.addEmployee(employee); 
    } 

    public List<Employee> listEmployeess() { 
     return employeeDao.listEmployeess(); 
    } 

    public Employee getEmployee(int empid) { 
     return employeeDao.getEmployee(empid); 
    } 

    public void deleteEmployee(Employee employee) { 
    employeeDao.deleteEmployee(employee); 
    } 
} 

我have't MVC的很多知識，請幫我 謝謝提前

Answer 1

您還沒有處理Transaction正確，這是造成問題的，所以在你EmployeeDaoImpl，你需要移動addEmployee()和deleteEmployee()內的Transaction代碼，如下圖所示：

@Repository("employeeDao") 
public class EmployeeDaoImpl implements EmployeeDao { 
    @Autowired 
    private SessionFactory sessionFactory; 

    public void addEmployee(Employee employee) { 
     Session session = sessionFactory.getCurrentSession(); 
     Transaction tx = session.beginTransaction(); 
     sessionFactory.getCurrentSession().saveOrUpdate(employee); 
     tx.commit(); 
    } 

    @SuppressWarnings("unchecked") 
    public List<Employee> listEmployeess() { 
     Session session = sessionFactory.getCurrentSession(); 
     Transaction tx = session.beginTransaction(); 
     Criteria criteria = session.createCriteria(Employee.class); 
     List<Employee> list = (List<Employee>)criteria.list(); 
     tx.commit(); 
     return list; 
    } 

    public Employee getEmployee(int empid) { 
     return (Employee) sessionFactory.getCurrentSession().get(Employee.class, empid); 
    } 

    public void deleteEmployee(Employee employee) { 
     Session session = sessionFactory.getCurrentSession(); 
     Transaction tx = session.beginTransaction(); 
     Query query = session.createQuery("Delete Employee where empid=:empid"); 
     query.setParameter("empid", employee.getEmpId()); 
     int result = query.executeUpdate(); 
     tx.commit(); 
    } 
} 

作爲最佳實踐，您可以利用@Transactional註釋，而不是手動處理的交易，你可以看看here

Answer 2

堆棧跟蹤抱怨有你沒有關

[com.daoImp.EmployeeDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException 

構造在這裏誤導爲EmployeeDaoImpl實現了任何約束。

我想這個問題發生在java/spring嘗試爲字段tx執行下面的行時。

Transaction tx = sessionFactory.getCurrentSession().beginTransaction(); 

在此階段，sessionFactory仍然爲空，並且將在後面的階段自動裝配。如果它是容器（tomcat + spring + hibernate）負責執行它（調用tx.commit（）;也應該是avid），那麼你不應該與事務處理進行交互。建議使用@Transactional註釋。

我建議以下的例子一樣

http://howtodoinjava.com/jpa/spring-hibernate-jpa-configuration-example/

Answer 3

org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.dao.EmployeeDao com.serviceImpl.EmployeeServiceImpl.employeeDao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeDao' defined in file [/Users/mohammad.waseem/Downloads/apache-tomcat-8.5.6/webapps/crud/WEB-INF/classes/com/daoImp/EmployeeDaoImpl.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.daoImp.EmployeeDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException 
    org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:506) 

我猜問題Employee對象。在方法（prepareModel）中檢查調試到你的控制器。看看你的實體。在Employee類中不存在構造函數，並且更改方法名稱（公共Employee getEmployee（int empid））。慢慢確認你的代碼。