Question

我是Struts和hibernate的新手。现在我正在做的是遵循一个教程来集成struts和hibernate并获得一个空指针Exception。我得到的错误是

 Sep 24, 2013 12:25:54 AM com.sun.faces.config.ConfigureListener contextInitialized
INFO: Initializing Sun's JavaServer Faces implementation (1.2_03-20070706-NIGHTLY)         for    context '/BookShop'
url isnull
log4j:WARN No appenders could be found for logger         (org.hibernate.type.BasicTypeRegistry).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
null
 <Sep 24, 2013 12:27:01 AM IST> <Error> <org.apache.struts2.dispatcher.Dispatcher>         <BEA-000000> <Exception occurred during     processing request: null
 java.lang.NullPointerException
at com.author.action.AuthorAction.listAuthor(AuthorAction.java:71)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
Truncated. see log file for complete stacktrace
>

目录结构：

enter image description here

操作文件AuthorAction.java：

package com.author.action;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import org.apache.struts2.ServletActionContext;
import org.hibernate.Session;
import org.hibernate.SessionFactory;


import com.author.listener.HibernateListener;
import com.author.model.Author;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;

@SuppressWarnings({ "serial", "unchecked" })
public class AuthorAction extends ActionSupport implements ModelDriven{

Author author = new Author();
List<Author> authorList = new ArrayList<Author>();

public String execute() throws Exception {
    return SUCCESS;
}

public Object getModel() {
    return author;
}
public List<Author> getAuthorList() {
    return authorList;
}

public void setAuthorList(List<Author> authorList) {
    this.authorList = authorList;
}

//save customer
public String addAuthor() throws Exception{

    //get hibernate session from the servlet context
    SessionFactory sessionFactory = 
         (SessionFactory) ServletActionContext.getServletContext()
                 .getAttribute(HibernateListener.KEY_NAME);

    Session session = sessionFactory.openSession();

    //save it
    author.setCreatedDate(new Date());

    session.beginTransaction();
    System.out.println("the value which is to be saved is"+author);
    session.save(author);
    session.getTransaction().commit();

    //reload the customer list
    authorList = null;
    authorList = session.createQuery("from author").list();
    System.out.println(" the author list is"+authorList);
    return SUCCESS;

}

//list all customers
public String listAuthor() throws Exception{

    //get hibernate session from the servlet context
    SessionFactory sessionFactory = 
         (SessionFactory) ServletActionContext.getServletContext()
                 .getAttribute(HibernateListener.KEY_NAME);

    Session session = sessionFactory.openSession();

    authorList = session.createQuery("from author").list();

    return SUCCESS;

}




}

Hibernate侦听器文件：

package com.author.listener;

import java.net.URL;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateListener implements ServletContextListener{

private Configuration config;
private SessionFactory factory;
private String path = "src/resources/hibernate.cfg.xml";
@SuppressWarnings("unchecked")
private static Class clazz = HibernateListener.class;

public static final String KEY_NAME = clazz.getName();

public void contextDestroyed(ServletContextEvent event) {
  //
}

public void contextInitialized(ServletContextEvent event) {

 try { 
        URL url = HibernateListener.class.getResource(path);
        System.out.println("url is"+url);
        config = new Configuration().configure(url);

        factory = config.buildSessionFactory();

        //save the Hibernate session factory into serlvet context
        event.getServletContext().setAttribute(KEY_NAME, factory);
  } catch (Exception e) {
         System.out.println(e.getMessage());
   }
}
}

我的模型文件Author.java：

package com.author.model;
import java.util.Date;
public class Author{
private Long customerId;
private String name;
private String address;
private Date createdDate;
public Long getCustomerId() {
    return customerId;
}
public void setCustomerId(Long customerId) {
    this.customerId = customerId;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public String getAddress() {
    return address;
}
public void setAddress(String address) {
    this.address = address;
}
public Date getCreatedDate() {
    return createdDate;
}
public void setCreatedDate(Date createdDate) {
    this.createdDate = createdDate;
}
}

hibernate.cfg.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
 "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <property name="hibernate.bytecode.use_reflection_optimizer">false</property>
    <property name="hibernate.connection.password">root</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/bookshop</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="use_sql_comments">false</property>
   <mapping resource="com/author/hibernate/Author.hbm.xml" />
  </session-factory>
</hibernate-configuration>

Hibernate映射文件Author.hbm.xml：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.mkyong.customer.model.Customer" 
table="customer" catalog="mkyong">

    <id name="customerId" type="java.lang.Long">
        <column name="CUSTOMER_ID" />
        <generator class="identity" />
    </id>
    <property name="name" type="string">
        <column name="NAME" length="45" not-null="true" />
    </property>
    <property name="address" type="string">
        <column name="ADDRESS" not-null="true" />
    </property>
    <property name="createdDate" type="timestamp">
        <column name="CREATED_DATE" length="19" not-null="true" />
    </property>
</class>
</hibernate-mapping>

JSP文件Author.jsp：

<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
</head>

<body>
<h1>Struts 2 + Hibernate integration example</h1>

 <h2>Add Customer</h2>
 <s:form action="addAuthorAction" >
     <s:textfield name="name" label="Name" value="" />
 <s:textarea name="address" label="Address" value="" cols="50" rows="5" />
  <s:submit />
</s:form>

 <h2>All Customers</h2>

<s:if test="authorList.size() > 0">
 <table border="1px" cellpadding="8px">
    <tr>
    <th>Customer Id</th>
    <th>Name</th>
    <th>Address</th>
    <th>Created Date</th>
</tr>
<s:iterator value="authorList" status="userStatus">
    <tr>
        <td><s:property value="customerId" /></td>
        <td><s:property value="name" /></td>
        <td><s:property value="address" /></td>
        <td><s:date name="createdDate" format="dd/MM/yyyy" /></td>
    </tr>
</s:iterator>
</table>
</s:if>
<br/>
<br/>

</body>
</html>

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>
  <constant name="struts.devMode" value="false" />

  <package name="default" namespace="/" extends="struts-default">

    <action name="addAuthorAction" 
class="com.author.action.AuthorAction" method="addAuthor" >
   <result name="success">pages/Author.jsp</result>
</action>

<action name="listAuthorAction" 
class="com.author.action.AuthorAction" method="listAuthor" >
    <result name="success">pages/Author.jsp</result>
</action>       

  </package>    
</struts>

web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Bookshop</display-name>

  <filter>
<filter-name>struts2</filter-name>
<filter-class>
  org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
</filter-class>
  </filter>

  <filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
  </filter-mapping>

  <listener>
    <listener-class>com.author.listener.HibernateListener
     </listener-class>
   </listener>

</web-app>

Answer 1

我们在2013年，因此您不需要使用XML来描述您的Hibernate模型，并且您不需要XML来定义您的Struts2操作（请参阅Struts2 Convention Plugin）。

要处理你的Hibernate Session（看起来这是你的问题）你可以使用Struts2 Hibernate插件，只需编写一个Interceptor for Session Handling或我首选的解决方案使用Spring作为DI，让spring注入你的存储库并处理你的会话

作为一个现实生活中的例子，请看一下Struts2 Todo App。

Answer 2

在您的代码中，您无法构建会话工厂，因此NullPointerException。

这是一个常见错误，这意味着代码中出现了错误。在上面的代码中，您可以在context initialize事件上构建会话工厂，而不是将其委派给HibernateUtil，这是手动构建会话工厂的推荐方法。

在this回答中解释了如何构建会话工厂。

要在配置Hibernate时修复错误，您需要编写以下代码：

config = new Configuration().configure("/hibernate.cfg.xml");

hibernate.cfg.xml文件应该在类路径中，就像你的例子一样。

struts 2与hibernate 3空指针异常集成

2 个答案: