很简单的SSH问题 java.lang.NullPointerException 在线等！！！

Question

login.jsp <s:form action="register" method="post">
  <s:textfield name="user.username" label="用户名"/>
  <s:password name="user.password" label="密码"/>
  <s:submit value="注册"/>
  <s:reset value="重填"/>
  </s:form>struts.xml<package name="default" extends="struts-default">
<action name="register" class="action.RegisterAction">
<result name="success">/success.jsp</result>
</action>
ApplicationContext.xml<bean id="userDao" class="Realized.UserDaoHibernate" />
<bean id="User" class="bean.User"/><bean id="registerAction" class="action.RegisterAction"><property name="user" ref="User"/>
<property name="userDao" ref="userDao"/>
</bean>
RegisterAction.javapackage action;import javax.annotation.Resource;import bean.User;import com.opensymphony.xwork2.ActionSupport;import dao.UserDao;public class RegisterAction extends ActionSupport {
/**
 * 
 */
private static final long serialVersionUID = 1L;
private UserDao userDao;
    public UserDao getUserDao() {
return userDao;
}
    @Resource
public void setUserDao(UserDao userDao) {
this.userDao = userDao;
}
private User user;
public User getUser() {
return user;
}
@Resource
public void setUser(User user) {
this.user = user;
}
public String execute() throws Exception
{
   userDao.saveUser(user);
   return SUCCESS;
}
}

Answer 1

private User user;
把这个属性及相关的方法从Action中删除掉。

Answer 2

补充：错误是
java.lang.NullPointerException
action.RegisterAction.execute(RegisterAction.java:34)
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:441)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:280)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:243)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:165)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:252)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:179)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:130)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:165)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:179)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:488)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)
web.xml
 <filter>
   <filter-name>struts2</filter-name>
   <filter-class>
   org.apache.struts2.dispatcher.FilterDispatcher
   </filter-class>
  </filter>
  <filter-mapping>
   <filter-name>struts2</filter-name>
   <url-pattern>/*</url-pattern>
  </filter-mapping>
 
  <listener>
  <listener-class>
  org.springframework.web.context.ContextLoaderListener
  </listener-class>
  </listener>

Answer 3

弱弱问一下 如果删掉user 那么userDao.saveUser(user) 这个user从哪来

Answer 4

你把 @Resource
    public void setUser(User user) {
        this.user = user;
    }
这的 @Resource去掉呢

Answer 5

  <filter-mapping>
      <filter-name>struts2</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>
改成
  <filter-mapping>
      <filter-name>struts2</filter-name>
      <url-pattern>*.action</url-pattern>
  </filter-mapping>
试一下吧，好像被拦截器拦截了

Answer 6

去掉@Resource没有反应
然后改成*.action报错 在打开login.jsp时 The Struts dispatcher cannot be found. 

Answer 7

    @Resource
    public void setUser(User user) {
        this.user = user;
    }
把@Resource去掉，你的user对象是要从页面上获得，而不是用@Resource标签从spring依赖注入

Answer 8

从配置上看不到什么错。感觉更像是少了什么JAR包

Answer 9

另外你的spring配置文件修改为
<bean id="userDao" class="Realized.UserDaoHibernate" /><bean id="registerAction" class="action.RegisterAction" scope="prototype">
<property name="userDao" ref="userDao"/>
</bean>

Answer 10

我在奇怪这样写为什么IDE没给你错误提示，userDao.saveUser(user);    变量要先初始化再使用，给private User user 初始化为：private User user = null试试;

Answer 11

你用了ApplicationContext ctx=new ClassPathXmlApplicationContext("bean文件路径");
来加载xml文件了么

Answer 12

    public String execute() throws Exception
    {
       ApplicationContext ctx=new ClassPathXmlApplicationContext("bean文件路径");
       this.userDao = ctx.getBean("userDao");
       userDao.saveUser();
       return SUCCESS;
    }
这样试试呢?

Answer 13

你有打开注解么？？如果没有打开的话那个@Resource是没用的。

Answer 14

是否缺少 struts2 的一个插件， struts2-spring-plugin-x-x-x.jar
此插件用来整合Spring 与 Struts2

Answer 15

修改一下这里就可以了：
<package name="default" extends="struts-default">
<action name="register" class="registerAction">
<result name="success">/success.jsp</result>
</action>
这样的做法是你直接应用了spring的代理。

Answer 16

//个人认为应该把这两个注解都去掉，应为你已经在xml文件中注入了，就不需要了，只需要有set方法就可以
@Resource
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
    private User user;
    public User getUser() {
        return user;
    }
    @Resource
    public void setUser(User user) {
        this.user = user;
    }

Answer 17

建议断点调试一下，这样的话可以知道那个地方是Null

Answer 18

你这个明显是报的空指针 
    public String execute() throws Exception
    {
       userDao.saveUser(user);
       return SUCCESS;
    }userDao.saveUser(user);
检查这一行 
按报告来说 感觉是userDao的控制正 也不排除 user的空指针 
实体还能注意给action  这个没用这样用过 运用感觉不是那么灵活

Answer 19

一种情况，你spring没能创建User对象;
二种直接new ：如下 
public void setUser(User user) {
        this.user = new User();
    }
在setUser(User user )中new User();

Answer 20

同上楼，遇到这个问题，网上说的问题都比较多，最多的是把action类型改成委托类型，不过感觉要改的地方挺多的。