org.hibernate.MappingException: Unknown entity: com.freemark.model.User

org.hibernate.MappingException: Unknown entity: com.freemark.model.User
	at org.hibernate.internal.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:1096)
	at org.hibernate.internal.SessionImpl.getEntityPersister(SessionImpl.java:1479)
	at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:117)
	at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:209)
	at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:55)
	at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:194)
	at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:49)
	at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
	at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:715)
	at org.hibernate.internal.SessionImpl.save(SessionImpl.java:707)
	at org.hibernate.internal.SessionImpl.save(SessionImpl.java:702)
	at com.freemark.dao.UseDao.addUser(UseDao.java:34)
	at com.freemark.controller.FreeMarkController.test(FreeMarkController.java:45)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:151)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:957)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:722)

 遇到如上的报错问题，先展示一下我的User类：

package com.freemark.model;



import java.util.Date;

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


import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;
import org.springframework.format.annotation.DateTimeFormat;
     


@Entity
@Table(name = "t_users")
public class User {

     private String id; 
     private String name; 
     private String password; 
     private Byte isactive; 
     @DateTimeFormat(pattern="yyyy-MM-dd") 
     private Date birth;
  
     @GenericGenerator(name = "generator", strategy = "uuid.hex")
 	 @Id
 	 @GeneratedValue(generator = "generator")
     @Column(name="id", unique=true, nullable=false, length=32)
     public String getId(){
     
     return id;
     
     
    }
    public User(String id){
      this.id=id;
     }
    
    public User(){}
    
    
    public void setId(String id){
    
       this.id=id;
    }
 
    @Column(name="name", length=50)
    public String getName(){
     
     return name;
    }
    
    
    public void setName(String name){
    
       this.name=name;
    }
 
    @Column(name="password", length=50)
    public String getPassword(){
     
     return password;
    }
    
    
    public void setPassword(String password){
    
       this.password=password;
    }
 
    @Column(name="isactive", length=3)
    public Byte getIsactive(){
     
     return isactive;
    }
    
    
    public void setIsactive(Byte isactive){
    
       this.isactive=isactive;
    }
 
    @Column(name="birth", length=10)
    public Date getBirth(){
     
     return birth;
    }
    
    
    public void setBirth(Date birth){
    
       this.birth=birth;
    }
 
	
   
}

 这里要注意Import引入的包名，我这里引入的包名是正确的，这个报错是因为，sessionFactory中没有这个类，解决办法：

<!-- 配置SessionFactory sessionFactory-->
	<bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
		<property name="dataSource" ref="dataSource" />
		<!-- <property name="hibernateProperties">
			<props>
				<prop key="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</prop>
				<prop key="hibernate.hbm2ddl.auto">update</prop>
				<prop key="hibernate.show_sql">true</prop>
				<prop key="hibernate.format_sql">true</prop>
			</props>
		</property>
		<property name="annotatedClasses">
			<list>
				<value>com.freemark.model.User</value>
			</list>
		</property> -->
		
		<property name="packagesToScan">
			<list> 
				<value>com.freemark.model</value>
			</list>
		</property>
	</bean>

 注意上面红色字体的部分（或者是span标签包住的部分），让sessionFactory来扫描这个包下面的类。问题解决！