Question

I am new to sturts2 and hibernate frameworks. I am making test web application. I have one model class ‘UserDetails’ one DAO class one Implementation of DAO and action class. And when saving object to database I’m getting the following error:

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 – implementation class

    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;
    }
}

Action class is

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 */

And when I press save button the following error occurs

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)

What maybe wrong? Thanks in advance.

Answer 1

Line 26 is doing

userDao.saveUser( user );

and it throws a NullPointerException. That means something which should not be null is null. What could be null in this line of code? userDao of course.

Have you initialized userDao somewhere? No. The line

private UserDetailsDao userDao;

is equivalent to

private UserDetailsDao userDao = null;

Initialize your userDao variable.