求助！第一个hibernate程序报错 org.hibernate.MappingException: Unknown entity: com.pojo.User

<!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>
<!-- 配置数据库连接信息-->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate4</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>

<mapping resource="com/pojo/User.hbm.xml"/>
</session-factory>
</hibernate-configuration>

package com.pojo;

public class User {
private int id;
private String name;
private String pwd;

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 getPwd() {
return pwd;
}
public void setPwd(String pwd) {
this.pwd = pwd;
}
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name="com.pojo.User_po" table="user">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"/>
<property name="pwd"/>
</class>
</hibernate-mapping>

package com.test;

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 com.pojo.User;

public class Test {
public static void main(String[] args) {

Configuration cfg=new Configuration().configure();

ServiceRegistry sr=new StandardServiceRegistryBuilder()
.applySettings(cfg.getProperties())
.build();
SessionFactory sf=cfg.buildSessionFactory(sr);

Session session=sf.openSession();

Transaction tx=session.beginTransaction();

User user=new User();
user.setName("hibernate测试");
user.setPwd("admin");

session.save(user);

tx.commit();

session.close();
}
}

Exception in thread "main" org.hibernate.MappingException: Unknown entity: com.pojo.User
at org.hibernate.metamodel.internal.MetamodelImpl.entityPersister(MetamodelImpl.java:620)
at org.hibernate.internal.SessionImpl.getEntityPersister(SessionImpl.java:1627)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:104)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:192)
at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:38)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:177)
at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:32)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:73)
at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:682)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:674)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:669)
at com.test.Test.main(Test.java:36)