Hibernate报错org.hibernate.MappingException: Unknown entity解决方法

今天看视频教程学习了一下Hibernate，按照视频教程中的代码写，老师测试通不过，老报错，苦苦找不到原因，最终经过一个下午一个晚上的时间找出了原因，遂记录一下，希望帮助到有需要的人。

先说下报错： 
org.hibernate.MappingException: Unknown entity

这句报错的原因是映射没有成功，查看Bean和Hibernate的主配置文件和映射配置文件如下：

Students.java

package cn.codekong.entity;/** * 学生类 * @author szh * */public class Students{    private int sid;    private String sname;    private String gender;    private String address;    public Students() {    }    public Students(int sid, String sname, String gender, String address) {        super();        this.sid = sid;        this.sname = sname;        this.gender = gender;        this.address = address;    }    public int getSid() {        return sid;    }    public void setSid(int sid) {        this.sid = sid;    }    public String getSname() {        return sname;    }    public void setSname(String sname) {        this.sname = sname;    }    public String getGender() {        return gender;    }    public void setGender(String gender) {        this.gender = gender;    }    public String getAddress() {        return address;    }    public void setAddress(String address) {        this.address = address;    }    @Override    public String toString() {        return "Students [sid=" + sid + ", sname=" + sname + ", gender=" + gender + ", address=" + address + "]";    }}
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hibernate.cfg.xml

<?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.username">root</property>        <property name="connection.password">root</property>        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>        <property name="connection.url">jdbc:mysql:///hibernate?useUnicode=true&amp;characterEncoding=UTF-8</property>        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>        <property name="show_sql">true</property>        <property name="format_sql">true</property>        <property name="hbm2ddl.auto">create</property>        <mapping resource="cn/codekong/entity/Students.hbm.xml"/>    </session-factory></hibernate-configuration>
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Students.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"><!-- Generated 2017-4-2 18:05:47 by Hibernate Tools 3.5.0.Final --><hibernate-mapping>    <class name="cn.codekong.entity.Students" table="STUDENTS">        <id name="sid" type="int">            <column name="SID" />            <generator class="assigned" />        </id>        <property name="sname" type="java.lang.String">            <column name="SNAME" />        </property>        <property name="gender" type="java.lang.String">            <column name="GENDER" />        </property>        <property name="address" type="java.lang.String">            <column name="ADDRESS" />        </property>    </class></hibernate-mapping>
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StudentsTest.java

import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.junit.After;import org.junit.Before;import org.junit.Test;import cn.codekong.entity.Students;public class StudentsTest {    private SessionFactory sessionFactory;    private Session session;    private Transaction transaction;    @Before    public void init() {        //创建配置对象        Configuration configuration = new Configuration().configure();        //创建服务注册对象        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();        //创建会话工厂对象        sessionFactory = configuration.buildSessionFactory(serviceRegistry);        //会话对象        session = sessionFactory.openSession();        //开启事物        transaction = session.beginTransaction();    }    @After    public void destory() {        //提交事物        transaction.commit();        //关闭会话        session.close();        //关闭会话工厂        sessionFactory.close();    }    @Test    public void testSaveStudents() {        //生成学生对象        Students student = new Students(1, "张三丰", "男", "武当山");        System.out.println(student);        session.save(student);        System.out.println(session);    }}
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上面的代码看其实确实是对的，但是就是测试跑不通，最终发现是版本问题 ，对，版本问题，视频里面是Hibernate3.x，而我使用的是Hibernate5.x，所以代码有变化。

说明一下，上面的代码在Hibernate5.x以下是可以运行的，但是在Hibernate5.x以后，必须写成如下的形式：

import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.boot.MetadataSources;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.service.ServiceRegistry;import org.junit.After;import org.junit.Before;import org.junit.Test;import cn.codekong.entity.Students;public class StudentsTest {    private SessionFactory sessionFactory;    private Session session;    private Transaction transaction;    @Before    public void init() {//在5.1.0版本汇总，hibernate则采用如下新方式获取：    //1. 配置类型安全的准服务注册类，这是当前应用的单例对象，不作修改，所以声明为final    //在configure("cfg/hibernate.cfg.xml")方法中，如果不指定资源路径，默认在类路径下寻找名为hibernate.cfg.xml的文件    final StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure("cfg/hibernate.cfg.xml").build();    //2. 根据服务注册类创建一个元数据资源集，同时构建元数据并生成应用一般唯一的的session工厂    SessionFactory sessionFactory = new MetadataSources(registry).buildMetadata().buildSessionFactory();    /****上面是配置准备，下面开始我们的数据库操作******/    Session session = sessionFactory.openSession();//从会话工厂获取一个session    Transaction transaction = session.beginTransaction();//开启一个新的事务    }    @After    public void destory() {        //提交事物        transaction.commit();        //关闭会话        session.close();        //关闭会话工厂        sessionFactory.close();    }    @Test    public void testSaveStudents() {        //生成学生对象        Students student = new Students(1, "张三丰", "男", "武当山");        System.out.println(student);        session.save(student);        System.out.println(session);    }
}