封装Util获取session工厂

• 采用单例模式（保证外部调用的方法中不包含new操作，new操作只执行一次，比如让它随着类的加载而执行）

  public class HibernateUtil {
  
      //静态域，随着类的加载而加载；类的所有实例共享一个sqlSessionFactory，一个对象对其修改则所有对象的该域都被修改。常量，调用对象构造器初始化后不能更改
      private static final SessionFactory sessionFactory=buildSessionFactory();
  
      private static SessionFactory buildSessionFactory() {
          Configuration configuration=new Configuration().configure();
          ServiceRegistry serviceRegistry=new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
          return configuration.buildSessionFactory(serviceRegistry);    
      }
  
      //这样获取的就都是单例了
      public static SessionFactory getSessionFactory() {
          return sessionFactory;
      }
  
  }
  

  Crud

  public class StudentTest {
  

  private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();

  private void add() {

  Session session=sessionFactory.openSession();
  session.beginTransaction();
  
  Student s=new Student();
  s.setName("李四");
  session.save(s);
  
  session.getTransaction().commit();
  session.close();
  

  }

  private void delete() {

  Session session=sessionFactory.openSession();
  session.beginTransaction();
  
  Student s=(Student)session.get(Student.class, Long.valueOf(1));
  session.delete(s);
  
  session.getTransaction().commit();
  session.close();
  

  }

  private void update() {

  Session session=sessionFactory.openSession();
  session.beginTransaction();
  
  Student s=(Student)session.get(Student.class, Long.valueOf(1));
  s.setName("张三2");
  session.save(s);
  
  session.getTransaction().commit();
  session.close();
  

  }

  private void getAllStudent() {

  Session session=sessionFactory.openSession();
  session.beginTransaction();
  
  String hql="from Student";
  Query query=session.createQuery(hql);
  List<Student> studentList=query.list();
  for(Student s:studentList) {
      System.out.println(s);
  }
  
  session.getTransaction().commit();
  session.close();
  

  }

  public static void main(String[] args) {

  StudentTest studentTest=new StudentTest();
  //studentTest.add();
  //studentTest.delete();
  //studentTest.update();
  studentTest.getAllStudent();
  

  }
  }

  session缓存

• 查询某条数据都是先到session缓存中查看是否存在，存在即引用，不存在再去数据库查询

  Student s1=(Student)session.get(Student.class, Long.valueOf(1)); //select语句查询
  Student s2=(Student)session.get(Student.class, Long.valueOf(2));
  Student s3=(Student)session.get(Student.class, Long.valueOf(1)); //在session缓存中获取
  System.out.println(s1==s2); //false
  System.out.println(s1==s3); //true
  

  代码实例

• eclipse->HibernateCrud