HIbernate4.2.7错误Connection cannot be null when 'hibernate.dialect' not set

今天在学习Hibernate的时候遇到一个错误，记录下来，开始养成写博客的习惯，错误的原因很简单。

错误内容如下：

org.hibernate.HibernateException: Connection cannot be null when 'hibernate.dialect' not set
at org.hibernate.service.jdbc.dialect.internal.DialectFactoryImpl.determineDialect(DialectFactoryImpl.java:98)
at org.hibernate.service.jdbc.dialect.internal.DialectFactoryImpl.buildDialect(DialectFactoryImpl.java:68)
at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:174)
at org.hibernate.service.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:76)
at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:160)
at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:132)
at org.hibernate.cfg.Configuration.buildTypeRegistrations(Configuration.java:1822)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1780)
at cn.yyx.hibernate.model.TeacherTest.test(TeacherTest.java:23)
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)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

主要原因参照第一行

Connection cannot be null when 'hibernate.dialect' not set。说是hibernate的dialect没有设置，但是在hibernate.cfg,xml中我已经配置了。主要内容如下：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernatedemo</property>
<property name="connection.username">root</property>
<property name="connection.password">222147</property>
<property name="connection.pool_size">1</property>
<property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
<property name="current_session_context_class">thread</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="hbm2ddl.auto">create</property>

<mapping class="cn.yyx.hibernate.model.Teacher"/>

</session-factory>

</hibernate-configuration>

Teacher.hbm.xml的配置如下：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name="cn.yyx.hibernate.model.Person" table="Person">
<id name="id" column="teacher_id">
<generator class="native"></generator>
</id>
<property name="name"></property>
<property name="title"></property>
</class>
</hibernate-mapping>

junit的测试代码如下：

package cn.yyx.hibernate.model;

import static org.junit.Assert.*;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.Test;

public class TeacherTest {

@Test
public void test() {
Teacher t = new Teacher();
t.setName("xxx");
t.setTitle("high");

Configuration cf = new Configuration();
ServiceRegistry sr = new ServiceRegistryBuilder().applySettings(cf.getProperties()) .buildServiceRegistry();
SessionFactory sf = cf.buildSessionFactory(sr);

Session s = sf.openSession();

s.beginTransaction();
s.save(t);
s.getTransaction().commit();
s.close();
sf.close();
}

}

model类的代码如下：

package cn.yyx.hibernate.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Teacher {
private int id;
private String name;
private String title;

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
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 String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}

}

因为看的视频是前几年的，所用的HIBERNATE的版本比较早，所以对于Hibernate4.2.7的配置变动不是很清楚，在查阅了资料后总结出了和视频中不同的地方，但是还是报错了。最后发现，是在因为在建立SessionFactory之前，我的Configration少读了一次hibernate.cfg.xml中的配置，不然就要去找hibernate.properties，但是我的项目中没有对应的文件，则发生错误（没有设置数据库方言）。

新的代码改为：

package cn.yyx.hibernate.model;

import static org.junit.Assert.*;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.Test;

public class TeacherTest {

@Test
public void test() {
Teacher t = new Teacher();
t.setName("xxx");
t.setTitle("high");

Configuration cf = new Configuration();
cf.configure();
ServiceRegistry sr = new ServiceRegistryBuilder().applySettings(cf.getProperties()) .buildServiceRegistry();
SessionFactory sf = cf.buildSessionFactory(sr);

Session s = sf.openSession();

s.beginTransaction();
s.save(t);
s.getTransaction().commit();
s.close();
sf.close();
}

}

测试通过，没有错误。增加了一句话：cf.configure();

总结：

在自学hibernate的时候， 资料的版本不对让进度上受到了很大的限制，英文的文档又不怎么看的懂。所以，要积攒之前的错误，尽量不要重复犯。也希望能找到人可以帮助指点一下。