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我是 sturts2 和休眠框架的新手。我正在制作测试网络应用程序。我有一个模型类“UserDetails”一个DAO 类一个DAO 和动作类的实现。将对象保存到数据库时，出现以下错误：

UserDetails.class

package org.project.model;

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

@Entity
@Table(name="user_details")
public class UserDetails {

private int userId;
private String userName;

@Id
@GeneratedValue
@Column(name="id")
public int getUserId() {
    return userId;
}

public void setUserId(int userId) {
    this.userId = userId;
}

@Column(name="name")
public String getUserName() {
    return userName;
}

public void setUserName(String userName) {
    this.userName = userName;
}
}

UserDetailsDaoImpl - 实现类

    package org.project.model.dao.iml;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.project.model.UserDetails;
import org.project.model.dao.UserDetailsDao;

import com.googlecode.s2hibernate.struts2.plugin.annotations.SessionTarget;
import com.googlecode.s2hibernate.struts2.plugin.annotations.TransactionTarget;

public class UserDetailsDaoImpl implements UserDetailsDao {

    @SessionTarget
    Session session;
    @TransactionTarget
    Transaction transaction;

    @Override
    public void saveUser(UserDetails user) {
        try {
            session.save(user);
        } catch (Exception e) {
            transaction.rollback();
            e.printStackTrace();
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public List<UserDetails> listUser() {
        List<UserDetails> users = null;
        try {
            users = session.createQuery("from UserDetails").list();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return users;
    }
}

动作类是

package org.project.actions;

import java.util.ArrayList;
import java.util.List;

import org.project.model.UserDetails;
import org.project.model.dao.UserDetailsDao;

import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;

public class UserAction extends ActionSupport implements ModelDriven<UserDetails>{

private static final long serialVersionUID = -2167265047934268752L;

private UserDetails user = new UserDetails();
private UserDetailsDao userDao;
private List<UserDetails> userList = new ArrayList<UserDetails>();

@Override
public UserDetails getModel(){
    return user;
}

public String add() {
    userDao.saveUser( user );
    return SUCCESS;
}

public String list() {
    userList = userDao.listUser();
    return SUCCESS;
}

public String execute(){
    return SUCCESS;
}

/* With all setter and getter methods */

当我按下保存按钮时，会发生以下错误

java.lang.NullPointerException
org.project.actions.UserAction.add(UserAction.java:26)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:440)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:279)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242)
com.googlecode.s2hibernate.struts2.plugin.s2hibernatevalidator.interceptor.HibernateValidatorInterceptor.intercept(HibernateValidatorInterceptor.java:77)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:163)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
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:236)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:148)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:93)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:128)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
org.apache.struts2.interceptor.ProfilingActivationInterceptor.intercept(ProfilingActivationInterceptor.java:104)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:148)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
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:236)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:128)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
com.googlecode.s2hibernate.struts2.plugin.interceptors.SessionTransactionInjectorInterceptor.intercept(SessionTransactionInjectorInterceptor.java:157)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:468)
org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(Stru     tsPrepareAndExecuteFilter.java:76)

可能有什么问题？提前致谢。

4

1 回答 1

3

第 26 行正在做

userDao.saveUser( user );

它抛出一个 NullPointerException。这意味着不应该为空的东西是空的。在这行代码中什么可能是空的？userDao当然。

您是否在某处初始化了 userDao？没有。这条线

private UserDetailsDao userDao;

相当于

private UserDetailsDao userDao = null;

初始化你的userDao变量。

于 2012-05-04T09:13:33.560 回答