提交表单时Struts 2 Hibernate空指针异常
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【中文标题】提交表单时Struts 2 Hibernate空指针异常【英文标题】：Struts 2 Hibernate null pointer exception while submitting the form 【发布时间】：2013-09-08 08:17:54 【问题描述】：我正在尝试通过集成 Struts 2 和 Hibernate 创建一个注册页面。但是当我运行下面的代码时，当我点击注册按钮时，我得到一个空指针异常。
休眠配置文件：
<hibernate-configuration>
<session-factory>
<property name="hibernate.dialect">org.hibernate.dialect.mysqlDialect</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost/db_socialnetwork</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>
<mapping resource="hibernate.hbm.xml"/>
</session-factory>
</hibernate-configuration>
休眠映射文件：
<hibernate-mapping>
<class name="models.User" table="tbl_user"> //DAO Class
<meta attribute="class-description">
This class contains a sample.
</meta>
<id column="user_id" name="id" type="int">
<generator class="increment"/>
</id>
<property column="user_name" name="name" type="string"/>
<property column="user_pwd" name="pwd" type="string"/>
<property column="user_email" name="email" type="string"/>
<property column="user_address" name="address" type="string"/>
<property column="user_phno" name="phno" type="int"/>
</class>
</hibernate-mapping>
struts.xml:
<struts>
<!-- Configuration for the default package. -->
<constant name="struts.devMode" value="true" />
<package name="default" extends="struts-default" namespace="/">
<action name="register" class="models.RegisterAction" method="execute">
<result name="success">/home.jsp</result>
</action>
</package>
</struts>
web.xml:
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<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>
<session-config>
<session-timeout>
30
</session-timeout>
</session-config>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
HibernateUtil:
public class HibernateUtil
private static final SessionFactory sessionFactory;
static
try
//new SchemaExport(config).create(true,true);
sessionFactory = new Configuration().configure().buildSessionFactory();
catch (Throwable ex)
// Log the exception.
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
public static SessionFactory getSessionFactory()
return sessionFactory;
注册表：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<s:form action="register">
<s:textfield name="name" label="Name"/>
<s:textfield name="pwd" label="Password"/>
<s:textfield name="email" label="Email"/>
<s:textarea name="address" label="Address"/>
<s:textfield name="phno" label="Mobile"/>
<s:submit value="Register"/>
</s:form>
</body>
</html>
RegisterAction:
public class RegisterAction extends ActionSupport implements ModelDriven<User>
User u = new User();
UserDao udao = new UserDao();
public RegisterAction()
public String execute() throws Exception
udao.addUser(u);
return "success";
@Override
public User getModel()
throw new UnsupportedOperationException("Not supported yet.");
public User getU()
return u;
public void setU(User u)
this.u = u;
User类：
public class User
int id, phno;
String name, pwd, email, address;
public String getAddress()
return address;
public void setAddress(String address)
this.address = address;
public String getEmail()
return email;
public void setEmail(String email)
this.email = email;
public int getId()
return id;
public void setId(int id)
this.id = id;
public String getName()
return name;
public void setName(String name)
this.name = name;
public int getPhno()
return phno;
public void setPhno(int phno)
this.phno = phno;
public String getPwd()
return pwd;
public void setPwd(String pwd)
this.pwd = pwd;
UserDao:
class UserDao
public UserDao()
public static void addUser(User u)
Session session = HibernateUtil.getSessionFactory().openSession();
Transaction t = session.beginTransaction();
int i = (Integer)session.save(u);
t.commit();
session.close();
数据库由以下字段组成：
id - 自动生成，int，主键 姓名， 密码， 电子邮件， 地址 - 字符串， phno - int显示的错误是：
INFO: Hibernate 3.2.5
INFO: hibernate.properties not found
INFO: Bytecode provider name : cglib
INFO: using JDK 1.4 java.sql.Timestamp handling
INFO: configuring from resource: /hibernate.cfg.xml
INFO: Configuration resource: /hibernate.cfg.xml
INFO: Reading mappings from resource : hibernate.hbm.xml
SEVERE: Error parsing XML: XML InputStream(17) The content of element type "class" must match "(meta*,subselect?,cache?,synchronize*,comment?,tuplizer*,(id|composite-id),discriminator?,natural-id?,(version|timestamp)?,(property|many-to-one|one-to-one|component|dynamic-component|properties|any|map|set|list|bag|idbag|array|primitive-array)*,((join*,subclass*)|joined-subclass*|union-subclass*),loader?,sql-insert?,sql-update?,sql-delete?,filter*,resultset*,(query|sql-query)*)".
SEVERE: Initial SessionFactory creation failed.org.hibernate.InvalidMappingException: Could not parse mapping document from resource hibernate.hbm.xml
WARNING: StandardWrapperValve[default]: PWC1406: Servlet.service() for servlet default threw exception
org.xml.sax.SAXParseException: The content of element type "class" must match "(meta*,subselect?,cache?,synchronize*,comment?,tuplizer*,(id|composite-id),discriminator?,natural-id?,(version|timestamp)?,(property|many-to-one|one-to-one|component|dynamic-component|properties|any|map|set|list|bag|idbag|array|primitive-array)*,((join*,subclass*)|joined-subclass*|union-subclass*),loader?,sql-insert?,sql-update?,sql-delete?,filter*,resultset*,(query|sql-query)*)".
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:198)
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:134)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:387)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:321)
at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.handleEndElement(XMLDTDValidator.java:2020)
at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.endElement(XMLDTDValidator.java:904)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1750)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2906)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:624)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:116)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:486)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:810)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:740)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:110)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1208)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:525)
at org.dom4j.io.SAXReader.read(SAXReader.java:465)
at org.hibernate.cfg.Configuration.addInputStream(Configuration.java:499)
at org.hibernate.cfg.Configuration.addResource(Configuration.java:566)
at org.hibernate.cfg.Configuration.parseMappingElement(Configuration.java:1587)
at org.hibernate.cfg.Configuration.parseSessionFactory(Configuration.java:1555)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1534)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1508)
at org.hibernate.cfg.Configuration.configure(Configuration.java:1428)
at org.hibernate.cfg.Configuration.configure(Configuration.java:1414)
at models.HibernateUtil.<clinit>(HibernateUtil.java:24)
at models.RegisterAction.<init>(RegisterAction.java:10)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:539)
at java.lang.Class.newInstance0(Class.java:372)
at java.lang.Class.newInstance(Class.java:325)
at com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:119)
at com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:150)
at com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:139)
at com.opensymphony.xwork2.ObjectFactory.buildAction(ObjectFactory.java:109)
at com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:288)
at com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:388)
at com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:187)
at org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:61)
at org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
at com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:47)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:478)
at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:717)
【问题讨论】：
【参考方案1】：您误解了 DAO/DTO 模式。 DAO/DTO 不应该是静态的。 sessionFactory 通常每个应用程序只构建一次更好，因为这是一个耗时的过程。
更好地实现session per thread pattern。编写HibernateUtil 类来构建sessionFactory 并获取会话。
那么你的 DAO 会是这样的
public class UserDao
public Session getSession()
return HibernateUtil.getSession();
public void closeSession()
HibernateUtil.closeSession();
public void addUser(User u)
Session session = getSession();
Transaction t = session.beginTransaction();
int i = (Integer)session.save(u);
t.commit();
closeSession();
在你写的动作中
private UserDao userDao = new UserDao();
public String execute() throws Exception
User u = new User();
u.setAddress(address);
u.setEmail(email);
u.setName(name);
u.setPhno(phno);
u.setPwd(pwd);
userDao.addUser(u);
return "success";
【讨论】：
错误现在是 org.hibernate.InvalidMappingException: 无法从资源 hibernate.hbm.xml 解析映射文档 罗马C：我试过了..它显示“org.xml.sax.SAXParseException：元素类型“类”的内容必须匹配“（元*，子选择？，缓存？，同步* ,comment?,tuplizer*,(id|composite-id),discriminator?,natural-id?,(version|timestamp)?,(property|many-to-one|one-to-one|component|dynamic-component |properties|any|map|set|list|bag|idbag|array|primitive-array)*,((join*,subclass*)|joined-subclass*|union-subclass*),loader?,sql-insert? ,sql-update?,sql-delete?,filter*,resultset*,(query|sql-query)*)".". 在 Hibernateutil 中，我已将 sessionfactory 、 session 对象和 getSession() & closeSession() 设为静态。除非我将这些设为静态，否则我无法在 userdao 中访问 getsession() 或 closesession .. 使用HibernateUtil 静态访问getSession() & closeSession()。你读过这个答案吗？它没有向您展示如何访问会话吗？【参考方案2】：
在RegisterAction 类中，您调用了静态方法UserDao.addUser(u)。 UserDao 类的 sf 字段仅在您调用 UserDao 的构造函数时才被初始化，但在您的情况下，构造函数永远不会被调用 => sf 永远不会被初始化，这就是为什么调用 sf.openSession(); 会抛出NullPointerException();
您应该在调用其方法之一之前初始化sf。
请注意，在非静态和/或非同步方法中初始化静态字段是一种非常糟糕的做法。
【讨论】：
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