Struts 2 Hibernate null pointer exception while su

2020-03-30 03:26发布

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问题:

I am trying to create a registration page by integrating Struts 2 & Hibernate. But when I am running the below code , I am getting a null pointer exception when I click the register button.

hibernate configuration file:

<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>

hibernate mapping file:

<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;
    }
}

Registration form:

<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 class:

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();
    }
}

The database consists of the following fields:

  • id - autogenerated , int , primary key
  • name,
  • pwd,
  • email,
  • address - string,
  • phno - int

Error being displayed is: 

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)

回答1:

You misunderstand the DAO/DTO pattern. DAO/DTOs should not be static. And the sessionFactory better build normally only once per application, because it's time consuming procedure.

Better for you to implement a session per thread pattern. Write the class HibernateUtil to build the sessionFactory and get the session.

Then your DAO will look like

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();
    }
}

in the action you write

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";
}


回答2:

In the class RegisterAction, you called the static method UserDao.addUser(u). The sf field of the UserDao class is only initialized when you call the constructor of UserDao, but in your case, the constructor is never called => the sf is never initialized thats why calling sf.openSession(); throws a NullPointerException();

You should initialize sf before calling one of its method.

Note that it is a very bad practice to initialize a static field in a no static and/or a no synchronized method.



标签： java hibernate jsp struts2 dao
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