Spring MVC 服务类 NullPointerException [关闭]答案

【问题标题】：Spring MVC Service class NullPointerException [closed]Spring MVC 服务类 NullPointerException [关闭]
【发布时间】：2016-05-23 02:51:54
【问题描述】：

我正在创建一个我遇到问题的应用程序。这是代码

HomeController.java

@Controller
public class HomeController {

    private EmployeeService employeeService;

    @Autowired(required=true)
    @Qualifier(value="employeeService")
    public void setEmployeeService(EmployeeService employeeService)
    {
        this.employeeService = employeeService;
    }

    @RequestMapping("/index")
    public ModelAndView indexWorld(@ModelAttribute("loginForm") Employee employee, ModelMap model) {

        return new ModelAndView("index", "welcomeMessage","Hello Guest! welcome to our site");
    }

    @RequestMapping("/login")
    public ModelAndView loginWorld(@ModelAttribute("loginForm") Employee employee, ModelMap model){

        String result="", returnPage="";
        if(this.employeeService.validateLogin(employee.getUsername(), employee.getPassword())){
            result = "Welcome " + employee.getUsername();
            returnPage = "home";
        }
        else{
            result = "<BR>Login Failure";
            returnPage = "index";
        }
        model.addAttribute("result", result);
        return new ModelAndView(returnPage, model);
    }
}

EmployeeServiceImpl.java

@Service
public class EmployeeServiceImpl implements EmployeeService {

    /* (non-Javadoc)
     * @see com.smart.service.EmployeeService#validateLogin(java.lang.String, java.lang.String)
     */

    EmployeeDAO employeeDAO;

    public void setEmployeeDAO(EmployeeDAO employeeDAO)
    {
        this.employeeDAO = employeeDAO;
    }

    @Override
    public boolean validateLogin(String username, String password) {
        // TODO Auto-generated method stub
        return this.employeeDAO.validateLogin(username, password);

    }    
}

EmployeeDAOImpl.java

@Transactional(value="myTransactionManager")
public class EmployeeDaoImpl implements EmployeeDAO {

    private SessionFactory sessionFactory;

    public void setSessionFactory(SessionFactory sessionFactory)
    {
        this.sessionFactory = sessionFactory;
    }
    @Override
    public boolean validateLogin(String username, String password) {

        return (long)this.sessionFactory.getCurrentSession().createQuery("SELECT COUNT(*) FROM EmployeeInfo WHERE username = :username AND password = :password")
        .setString("username", username)
        .setString("password", password).uniqueResult() > 0;

    }    
}

欢迎-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans     
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context 
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd"
    xmlns:mvc="http://www.springframework.org/schema/mvc">

    <context:annotation-config />
    <context:component-scan base-package="com.smart" />
    <mvc:annotation-driven />
    <tx:annotation-driven transaction-manager="myTransactionManager" />

    <bean id="employeeService" class="com.smart.service.EmployeeServiceImpl"></bean>
    <bean id="employeeDAO" class="com.smart.dao.EmployeeDaoImpl"></bean>

    <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
        <property name="sessionFactory" ref="sessionFactory" />
    </bean>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/view/" />
        <property name="suffix" value=".jsp" />
    </bean>

<bean id="sessionFactory"
        class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="configLocation">
            <value>classpath:hibernate.cfg.xml</value>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">${jdbc.dialect}</prop>
                <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
    </bean>

    <bean id="dataSource"
    class="org.springframework.jdbc.datasource.DriverManagerDataSource"
    p:driverClassName="oracle.jdbc.OracleDriver"
    p:url="jdbc:oracle:thin:@localhost:1521:IMS"
    p:username="username"
    p:password="password" />

    <mvc:resources mapping="/resources/**" location="/resources/theme1/" />
</beans>

错误

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:979)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

root cause

java.lang.NullPointerException
    com.smart.service.EmployeeServiceImpl.validateLogin(EmployeeServiceImpl.java:32)
    com.smart.controller.HomeController.loginWorld(HomeController.java:38)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:606)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

我正在这条线上进入 EmployeeServiceImpl.java

return this.employeeDAO.validateLogin(username, password);

似乎我从validateLogin 函数得到了空值，尽管我是来自validateLogin 函数的返回值。为什么我会变成 null？

编辑

现在错误

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'myTransactionManager' is defined: No matching PlatformTransactionManager bean found for qualifier 'myTransactionManager' - neither qualifier match nor bean name match!
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:979)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

root cause

org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'myTransactionManager' is defined: No matching PlatformTransactionManager bean found for qualifier 'myTransactionManager' - neither qualifier match nor bean name match!
    org.springframework.beans.factory.annotation.BeanFactoryAnnotationUtils.qualifiedBeanOfType(BeanFactoryAnnotationUtils.java:100)
    org.springframework.beans.factory.annotation.BeanFactoryAnnotationUtils.qualifiedBeanOfType(BeanFactoryAnnotationUtils.java:56)
    org.springframework.transaction.interceptor.TransactionAspectSupport.determineQualifiedTransactionManager(TransactionAspectSupport.java:377)
    org.springframework.transaction.interceptor.TransactionAspectSupport.determineTransactionManager(TransactionAspectSupport.java:358)
    org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:271)
    org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
    com.sun.proxy.$Proxy37.validateLogin(Unknown Source)
    com.smart.service.EmployeeServiceImpl.validateLogin(EmployeeServiceImpl.java:33)
    com.smart.controller.HomeController.loginWorld(HomeController.java:38)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:606)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

【问题讨论】：

What is a Null Pointer Exception, and how do I fix it?的可能重复
@FarazDurrani，它没有返回long，而是返回布尔值1>0 == true
您的第二个问题是因为您的 TransactionManager bean 的 id 为 transactionManager 但您的 @Transactional 注释的 bean 名称为 myTransactionManager
我再次收到之前的错误 NullPointerException。 @JamesEnl

标签： java spring hibernate spring-mvc

【解决方案1】：

似乎EmployeeDAO 没有注入EmployeeServiceImpl，使用@Autowire 或@Inject 连接EmployeeDAO，第二个EmployeeDAOImpl 尚未声明为组件（不确定您是否已在xml 中声明) 所以用@Repository 和@Autowire SessionFactory 声明它。希望这会做..

【讨论】：

@Autowire SessionFactory 工作！！

【解决方案2】：

从堆栈跟踪看来，您的代码从未在 dao 上调用 validateLogin。 dao 是空的，因为没有任何东西告诉 Spring 将您的 DAO 连接到您的服务中。将@Autowired 注释添加到dao 的服务中的setter，类似于您在将服务连接到其中的控制器中的内容。

【讨论】：

我在setEmployeeDAO(EmployeeDAO employeeDAO) 方法上方添加了@Autowired，现在我得到了不同的错误。我更新了上面的帖子。