Question

我正在编写一个应用程序在Spring 3和hibernate，当我尝试访问映射到“UserController”控制器的“用户”jsp页面时，我得到一个例外：

SEVERE: Servlet.service() for servlet [stbam] in context with path [/STBAM] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at com.gsimt.stbam.service.UserServiceImpl.listAllUsers(UserServiceImpl.java:16)
    at com.gsimt.stbam.controller.UserController.listUsers(UserController.java:24)
    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.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:440)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:428)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

这是我UserController.java:

的代码

package com.gsimt.stbam.controller;

import java.util.List;
import java.util.Map;

import org.springframework.stereotype.Controller;
import com.gsimt.stbam.domain.User;
import com.gsimt.stbam.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.servlet.ModelAndView;

@Controller
public class UserController {

    @Autowired
    private UserService userService;

     @RequestMapping("/users")
        public String listUsers(Map<String, Object> map) {

            map.put("user", new User());
            map.put("userList", userService.listAllUsers());

            return "users";
        }
}

UserService.java:

package com.gsimt.stbam.service;

import java.util.List;

import com.gsimt.stbam.domain.User;
import com.gsimt.stbam.dao.UserDao;
import org.springframework.beans.factory.annotation.Autowired;

public class UserServiceImpl implements UserService {

    @Autowired
    private UserDao userDao;

    public List<User> listAllUsers() {
        // TODO Auto-generated method stub
        return userDao.listUsers();
    }

    public User getUserById(Integer Id) {
        // TODO Auto-generated method stub
        return userDao.getUserById(Id);
    }

    public void addUser(User user) {
        // TODO Auto-generated method stub
        userDao.addOrUpdateUser(user);
    }

    public void deleteUser(Integer Id) {
        // TODO Auto-generated method stub
        userDao.deleteUser(Id);
    }

}

UserDao.java:

package com.gsimt.stbam.dao;

import java.util.List;

import com.gsimt.stbam.domain.User;

import org.hibernate.SessionFactory;
import org.springframework.stereotype.Repository;
import org.springframework.beans.factory.annotation.Autowired;

@Repository
public class UserDaoImpl implements UserDao{

    @Autowired
    private SessionFactory sessionFactory;

    public List<User> listUsers() {
        // TODO Auto-generated method stub
        return (List<User>)sessionFactory.getCurrentSession().createQuery("from User").list();
    }

    public User getUserById(Integer Id) {
        // TODO Auto-generated method stub
        User user = (User) sessionFactory.getCurrentSession().load(User.class, Id);
        return user;
    }

    public void addOrUpdateUser(User user) {
        // TODO Auto-generated method stub
        sessionFactory.getCurrentSession().saveOrUpdate(user);
    }

    public void deleteUser(Integer Id) {
        // TODO Auto-generated method stub
        User user = (User) sessionFactory.getCurrentSession().load(User.class, Id);
        if(user != null){

            sessionFactory.getCurrentSession().delete(user);
        }
    }

}

User.java

package com.gsimt.stbam.domain;

import java.io.Serializable;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Table;
import javax.persistence.Id;
import javax.persistence.Column;

@Entity
@Table (name = "USER")
public class User implements Serializable{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Id
    @Column (name = "ID")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer Id;

    @Column (name = "LOGIN")
    private String login;

    @Column (name = "FIRSTNAME")
    private String firstName;

    @Column (name = "LASTNAME")
    private String lastName;

    @Column (name = "EMAIL")
    private String email;

    @Column (name = "HASH")
    private String hash;

    public Integer getId() {
        return Id;
    }

    public void setId(Integer id) {
        Id = id;
    }

    public String getLogin() {
        return login;
    }

    public void setLogin(String login) {
        this.login = login;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getHash() {
        return hash;
    }

    public void setHash(String hash) {
        this.hash = hash;
    }


}

我的调度员背景stbam-servlet.xml：

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

    <context:annotation-config />
    <context:component-scan base-package="com.gsimt.stbam" />

    <bean id="jspViewResolver"
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="viewClass"
            value="org.springframework.web.servlet.view.JstlView" />
        <property name="prefix" value="/WEB-INF/views/" />
        <property name="suffix" value=".jsp" />
    </bean>

    <bean id="messageSource"
        class="org.springframework.context.support.ReloadableResourceBundleMessageSource">
        <property name="basename" value="classpath:messages" />
        <property name="defaultEncoding" value="UTF-8" />
    </bean>
    <bean id="propertyConfigurer"
        class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
        p:location="/WEB-INF/configuration.properties" />



    <tx:annotation-driven />

</beans>

最后我正在配置stbam-data.xml的{{1}}：

datasource and sessionfactory

我的web.xml：

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


  <bean id="dataSource"
        class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"
        p:driverClassName="com.mysql.jdbc.Driver"
        p:url="jdbc:mysql://localhost:3306/STBAMDB" p:username="root"
        p:password="123456" />


    <!-- to use hibernate 4, we have to use at least spring 3.2.2 The AnnotationSessionFactoryBean

    is not supported anymore and replaced by LocalSessionFactoryBean-->
    <bean id="sessionFactory"
          class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
            <property name="dataSource" ref="dataSource"></property>
            <property name="packagesToScan" value="com.gsimt.stbam.domain"></property>
            <property name="hibernateProperties">
                 <value>
                    hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect
                    hibernate.hbm2ddl.auto=update
                    hibernate.show_sql=true
                </value>
           </property>    
   </bean>

   <bean id="userDao"
         class="com.gsimt.stbam.dao.UserDaoImpl" />



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

  </beans>

我正在编写一个单元测试来测试UserDao和UserService，看起来好像很好，

提前致谢。

为了解决问题，我使用了3个弹簧配置文件：

用于持久性的stbam-data.xml。

用于声明服务bean的stbam-service.xml（包括userServiceImpl）。

即使我添加@Service和@Repositort（“userDao”）

，问题仍然存在

Answer 1

而不是

@Repository
public class UserDaoImpl implements UserDao{

使用

@Repository("userDao")
public class UserDaoImpl implements UserDao{

By Defualt UserDaoImpl的名称为userDaoImpl，因此not autowiring。

使用UserServiceImpl

注释@Service

或者在Spring XML中添加UserServiceImpl

此外，如果您使用Spring Annotations，则无需在XML中使用相同的bean声明

另外注意到你没有在stbam-data.xml内导入stbam-servlet.xml所以如果我没错，那么文件没有被使用......

在stbam-servlet.xml

中尝试以下内容

<import resource="classpath:stbam-data.xml" />

根据添加的web.xml文件（您缺少 COMMA ）试试吧。

<context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            /WEB-INF/stbam-service.xml,
            /WEB-INF/stbam-data.xml,
            /WEB-INF/stbam-security.xml
        </param-value>

</context-param>

Answer 2

使用UserServiceImpl刻板印象对@Service进行注释，使其符合自动装配的条件。

Answer 3

KEY：确保正在注入依赖项。

确保在WEB-INF内部调度程序servlet已打开＆＃34; context：component-scan＆＃34;以便按照上下文定义

通过弹簧拾取组件

<context:component-scan base-package="org.vimal.spring.controllers" /> 
Make sure the Controller class is annotated with @Controller 
Make sure service inside controller class is autowired

现在服务

Make sure Service class is annotated with @Service (@Component)
Make sure DAOs inside Service class is all @Autowired

这假设您的DAO正在运行，并且在被Web控制器调高之前已经过单元测试。

@Repository("recordsDao")
@Transactional (If hibernate is being used)
public class RecordsDao {
@Autowired
private SessionFactory sessionfactory;

java.lang.NullPointerException当我尝试访问映射到Controller的页面时

3 个答案: