java.lang.NullPointerException

Question

  SSH2项目整合
  jsp页面出现如下错误
com.study.action.StudentAction.execute(StudentAction.java:32)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:452)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:291)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:254)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:270)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:498)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:434)
  麻烦各位帮帮忙

Answer 1

com.study.action.StudentAction.execute(StudentAction.java:32)StudentAction.java 这个文件的第 32 行代码是啥？以及相关代码行。

Answer 2

 List list=studentService.query(username, password);

Answer 3

public class StudentDaoImpl extends HibernateDaoSupport implements StudentDao { @Override
public List query(String username, String password) {
// TODO Auto-generated method stub
   List list=(List)getHibernateTemplate().find("from Student student where student.name='"+username+"'");
  
   return list;
}

Answer 4

那就是说：
studentService 是NULL你可以：System.out.println("studentService: " + studentService); 看看
然后就是检查你的注入配置是否有问题了，为啥会导致没得到studentService。

Answer 5

applicationContext.xml文件
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
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">
  <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName">
<value>com.mysql.jdbc.Driver</value>
</property>
<property name="url">
<value>jdbc:mysql:///database</value>
</property>
<property name="username">
<value>root</value>
</property>
<property name="password">
<value>123456</value>
</property>
</bean>
<bean id="sessionFactory"
class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="hibernateProperties">
<props>
<prop key="hibernate.dialect">
org.hibernate.dialect.MySQLDialect
</prop>
<prop key="hibernate.show_sql">true</prop>
</props>
</property>
<property name="mappingResources">
<list>
<value>com/test/domain/Student.hbm.xml</value> </list>
</property>
</bean>
<bean id="studentdao" class="com.study.dao.impl.StudentDaoImpl">
<property name="sessionFactory" ref="sessionFactory"></property>
</bean>
<bean id="studentservice" class="com.study.service.impl.StudentServiceImpl">
<property name="studentDao" ref="studentdao"></property>
</bean>
<bean id="studentaction" class="com.study.action.StudentAction" scope="prototype">
<property name="studentService" ref="studentservice"></property>
</bean>

</beans>

Answer 6

  System.out.println("studentService: " + studentService);
  输出 null

Answer 7

问题都找出来了啊
studentService=null，你看看为什么会为null，看哪里注入值有问题

Answer 8

配置文件似乎没错。你是怎么定义StudentAction的？是用的Spring MVC 么？

Answer 9

public class StudentAction extends ActionSupport {
private StudentService studentService;
private String username;
private String password;
   
      
 @Override
public String execute() throws Exception {
// TODO Auto-generated method stub
 HttpServletRequest request=ServletActionContext.getRequest();
 request.setCharacterEncoding("utf-8");
 HttpSession session=request.getSession();
 session.setAttribute("username", username);
 session.setAttribute("password", password);
 ServletActionContext.getResponse().setCharacterEncoding("utf-8");
 System.out.println("studentService: " + studentService);
 System.out.println(password+"    "+username);
 List list=studentService.query(username, password);


 if(list.size()!=0)
 return SUCCESS;
 else
 return "register";

}

Answer 10

private StudentService studentService;
没提供set方法么？

Answer 11

lz，可以试试加上set方法。

Answer 12

你的注入写错了 
<bean id="studentaction" class="com.study.action.StudentAction" scope="prototype">
<property name="studentService" ref="studentservice"></property>
</bean>
 应改成 
<bean id="studentaction" class="com.study.action.StudentAction" scope="prototype">
<property name="studentDao" ref="studentdao"></property>
</bean>

Answer 13

不好意思楼主 我刚才看错了    估计是你的  studentService的注入的问题  看看自己的set 是否写错 
不过最好是让eclipse自动写   写完变量  右键 source->generator getters and setters

Answer 14

   很感谢大家的帮助，本人估计应该是application.xml配置文件有问题，但一直找不出来错误，好长时间没碰java了，学了编程，却做了物流管理，估计在编程上没有什么作为了。今天从朋友处拷了份SSH2的框架，终于跑起来了，赶快把毕业设计糊弄过去！！！
很感谢大家的帮忙