构建 SessionFactory 时出现 NullPointerException

Question

我使用 Hibernate 创建了一个简单的类示例，但出现以下错误：

Initial SessionFactory creation failed. java.lang.ExceptionInInitializerError
java.lang.ExceptionInInitializerError
    at org.hibernate.cfg.Configuration.reset(Configuration.java:249)
    at org.hibernate.cfg.Configuration.<init>(Configuration.java:216)
    at org.hibernate.cfg.Configuration.<init>(Configuration.java:220)
    at it.univaq.mwt.tplabs0.Test.main(Test.java:14)
Caused by: java.lang.NullPointerException
    at org.hibernate.util.ConfigHelper.getResourceAsStream(ConfigHelper.java:167)
    at org.hibernate.cfg.Environment.<clinit>(Environment.java:585)
    ... 4 more
Exception in thread "main" java.lang.NullPointerException
    at it.univaq.mwt.tplabs0.Test.main(Test.java:20)

我的测试课：

package it.univaq.mwt.tplabs0;

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

public class Test {

  public static void main(String[] args) {

    SessionFactory sessionFactory = null;

    try {
      sessionFactory = new Configuration().configure().buildSessionFactory();
    } catch (Throwable ex) {
      System.err.println("Initial SessionFactory creation failed. " + ex);
      ex.printStackTrace();
    }

    Session session = sessionFactory.getCurrentSession();
    session.beginTransaction();

    System.out.println("Creating element");
    Element el = new Element("prova", 1);

    session.save(el);
    System.out.println("Committing Tx");
    session.getTransaction().commit();

    System.out.println("Closing Session");
    if (session.isOpen())
        session.close();
  }
}

我的 Hibernate 配置文件：

<?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 name="">
        <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="hibernate.connection.password">master</property>
        <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:XE</property>
        <property name="hibernate.connection.username">master</property>
        <property name="hibernate.dialect">org.hibernate.dialect.OracleDialect</property>
        <property name="hbm2ddl.auto">create</property>
        <property name="current_session_context_class">thread</property>
     <mapping class="it.univaq.mwt.tplabs0.Element" resource="it/univaq/mwt/tplabs0/Element.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

我的图书馆：

• antlr-2.7.6.jar
• asm.jar
• asm-attrs.jar
• c3p0-0.9.1.jar
• cglib-2.2.jar
• commons-collections-3.1.jar
• commons-logging-1.0.4.jar
• concurrent-1.3.2.jar
• connector.jar
• dom4j-1.6.1.jar
• ehcache-1.2.3.jar
• hibernate3.jar
• jaas.jar
• javassist.jar
• jboss-cache.jar
• jboss-common.jar
• jboss-jmx.jar
• jboss-system.jar
• jdbc2_0-stdext.jar
• jgroups-2.2.8.jar
• jta.jar
• log4j-1.2.15.jar
• oscache-2.1.jar
• proxool-0.8.3.jar
• swarmcache-1.0rc2.jar
• slf4j-api-1.7.7.jar
• slf4j-log4j12-1.7.7.jar

启动这个简单的执行我从上面得到错误。我使用的数据库是 Oracle 11g。

发生了什么？

Answer 1

你的代码是怎么说的：

   1. SessionFactory sessionFactory = null;
   2.   try {
   3.     sessionFactory = new Configuration().configure().buildSessionFactory();
   4.   } catch (Throwable ex) {
   5.     System.err.println("Initial SessionFactory creation failed. " + ex);
   6.     ex.printStackTrace();
   7.   }
   8.          
   9.   Session session = sessionFactory.getCurrentSession();
        // Here you are trying to access the Session which is not even created

您正在尝试访问未在 CurrentSessionContext 中配置或根本未创建的 Session。

将第 9 行的代码替换为：

Session session = sessionFactory.openSession();

你会看透自己。