public void testQuery(){ 
  Session session=null; 
   
  try{ 
    session=HibernateUtils.getSession(); 
    session.beginTransaction(); 
     
    /** 
     * 会出现N+1问题，所谓的N+1值得是发出了N+1条sql语句 
     * 
     * 1：发出一条查询id列表的语句 
     * 
     * N：根据id发出N条sql语句，加载相关的对象 
     */ 
    Iterator iter=session.createQuery("from Student").iterate(); 
     
    while(iter.hasNext()){ 
      Student student=(Student)iter.next(); 
      System.out.println(student.getName()); 
    } 
    session.getTransaction().commit(); 
  }catch(Exception e){ 
    e.printStackTrace(); 
    session.getTransaction().rollback(); 
  }finally{ 
    HibernateUtils.closeSession(session); 
  } 
} 

public void testQuery(){ 
  Session session=null; 
   
  try{ 
    session=HibernateUtils.getSession(); 
    session.beginTransaction(); 
     
    List students=session.createQuery("from Student").list(); 
     
     
    System.out.println("---------------------------------"); 
    /** 
     * 避免了N+1问题 
     * 
     * 因为执行list操作后会将数据放到session的缓存中（一级缓存），所以采用iterate的时候 
     * 首先会发出一条查询id列表的语句，再根据id到缓存中加载相应的数据，如果缓存中存在与之匹配的数据 
     * 则不再发出根据id查询的sql语句，直接使用缓存中的数据 
     * 
     * Iterate方法如果缓存中存在数据，它可以提高性能，否则出现N+1问题 
     */ 
    //可以使用as别名 
    Iterator iter=session.createQuery("from Student").iterate(); 
     
    while(iter.hasNext()){ 
      Student student=(Student)iter.next(); 
      System.out.println(student.getName()); 
    } 
    session.getTransaction().commit(); 
  }catch(Exception e){ 
    e.printStackTrace(); 
    session.getTransaction().rollback(); 
  }finally{ 
    HibernateUtils.closeSession(session); 
  } 
} 

@SuppressWarnings({ "unchecked", "rawtypes" }) 
public void testQuery1(){ 
  Session session=null; 
   
  try{ 
    session=HibernateUtils.getSession(); 
    session.beginTransaction(); 
     
    //返回结果集属性列表，元素类型和实体类中的属性类型一致 
    List students=session.createQuery("from Student s where s.classes.name like '%2%'").list(); 
     
    for(Iterator ite=students.iterator();ite.hasNext();){ 
      Student obj=(Student)ite.next(); 
      System.out.println(obj.getName()); 
    } 
       
    session.getTransaction().commit(); 
  }catch(Exception e){ 
    e.printStackTrace(); 
    session.getTransaction().rollback(); 
  }finally{ 
    HibernateUtils.closeSession(session); 
  } 
} 

public void testQeury(){ 
  Session session=null; 
  try{ 
    session=HibernateUtils.getSession(); 
    session.beginTransaction(); 
     
    List list=session.createSQLQuery("select * from t_student").list(); 
     
    for(Iterator ite=list.iterator();ite.hasNext();){ 
      Object[] obj=(Object[])ite.next(); 
      System.out.println(obj[0]+","+obj[1]); 
    } 
     
    session.getTransaction().commit(); 
  }catch(Exception e){ 
    e.printStackTrace(); 
    session.getTransaction().rollback(); 
  }finally{ 
    HibernateUtils.closeSession(session); 
  } 
} 

//内连接 
@SuppressWarnings({ "unchecked", "rawtypes" }) 
public void testQuery(){ 
  Session session=null; 
   
  try{ 
    session=HibernateUtils.getSession(); 
    session.beginTransaction(); 
     
    //返回结果集属性列表，元素类型和实体类中的属性类型一致 
    List students=session.createQuery("select s.name,c.name from Student s join s.classes c").list(); 
     
    for(Iterator ite=students.iterator();ite.hasNext();){ 
      Object[] obj=(Object[])ite.next(); 
      System.out.println(obj[0]); 
    } 
     
    session.getTransaction().commit(); 
  }catch(Exception e){ 
    e.printStackTrace(); 
    session.getTransaction().rollback(); 
  }finally{ 
    HibernateUtils.closeSession(session); 
  } 
} 

@SuppressWarnings({ "unchecked", "rawtypes" }) 
public void testQuery(){ 
  Session session=null; 
   
  try{ 
    session=HibernateUtils.getSession(); 
    session.beginTransaction(); 
     
    //返回结果集属性列表，元素类型和实体类中的属性类型一致 
    List students=session.createQuery("select s.name,c.name from Student s left join s.classes c").list(); 
     
    for(Iterator ite=students.iterator();ite.hasNext();){ 
      Object[] obj=(Object[])ite.next(); 
      System.out.println(obj[0]); 
    } 
     
    session.getTransaction().commit(); 
  }catch(Exception e){ 
    e.printStackTrace(); 
    session.getTransaction().rollback(); 
  }finally{ 
    HibernateUtils.closeSession(session); 
  } 
} 

<?xml version="1.0"?> 
<!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.src.hibernate.Student" table="t_student"> 
    <id name="id"> 
      <generator class="native"/> 
    </id> 
    <property name="name"/> 
    <property name="createTime"></property> 
    <!-- 在多的一端Student中添加一行新的Classes列 ,并且列的名称要和Classes.hbm.xml的列明相同--> 
    <many-to-one name="classes" column="classesid"></many-to-one> 
  </class> 
   
  <query name="queryStudent"> 
    <![CDATA[ 
      select s from Student s where s.id<? 
    ]]> 
  </query> 
   
</hibernate-mapping> 

//外置命名查询 
@SuppressWarnings({ "unchecked", "rawtypes" }) 
public void testQuery(){ 
  Session session=null; 
   
  try{ 
    session=HibernateUtils.getSession(); 
    session.beginTransaction(); 
     
    List students=session.getNamedQuery("queryStudent").setParameter(0, 10).list(); 
     
    for(Iterator ite=students.iterator();ite.hasNext();){ 
      Student obj=(Student)ite.next(); 
      System.out.println(obj.getName()); 
    } 
     
    session.getTransaction().commit(); 
  }catch(Exception e){ 
    e.printStackTrace(); 
    session.getTransaction().rollback(); 
  }finally{ 
    HibernateUtils.closeSession(session); 
  } 
}