1.回顾jdbc开发 orm概述

　　orm是一种解决持久层对象关系映射的规则，而不是一种具体技术。jdbc/dbutils/springdao，hibernate/springorm，mybaits同属于ORM解决方案之一。

2.mybaits

　　mybatis基于jdbc，兼顾难易度和速度。

3.mybatis快速入门

　　导入lib包

　　在src目录下配置mybatis.cfg.xml

　　实体类

　　配置映射文件StudentMapper.xml

     
         
          
          
              
               
               
               
           
          
          
      
               INSERT INTO students(id,name,sal) values(1,"haha",7000)    
          
      
               INSERT INTO students(id,name,sal) values(#{id},#{name},#{sal})    
      
     

　　获取连接

public class MybatisUtil {    private static ThreadLocal
     
       threadLocal = new ThreadLocal
      
       ();    private static SqlSessionFactory sqlSessionFactory;    //加载位于mybatis.xml配置文件    static{        try {            Reader reader = Resources.getResourceAsReader("mybatis.cfg.xml");            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);        } catch (IOException e) {            throw new RuntimeException(e);        }    }    public static SqlSession getSqlSession(){                SqlSession sqlSession = threadLocal.get();        if(sqlSession == null){            sqlSession = sqlSessionFactory.openSession();            //将session与当前线程绑定在一起            threadLocal.set(sqlSession);        }        return sqlSession;    }    //关闭当前sqlsession，与当前线程分离    public static void closeSqlSession(){        SqlSession sqlSession = threadLocal.get();        if(sqlSession!=null){            sqlSession.close();            //分离，目的是为了尽早垃圾回收            threadLocal.remove();        }    }}
      
     

　　dao

public void add1() throws Exception{        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            //默认事务开始，读取StudentMapper.xml映射文件中的sql语句            int i = sqlSession.insert("studentNamespace.add1");            sqlSession.commit();            System.out.println("本次操作影响了"+i+"行");        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }    }    public void add2(Student student) throws Exception{        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            //默认事务开始，读取StudentMapper.xml映射文件中的sql语句            sqlSession.insert("studentNamespace.add2",student);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }    }

4.mybatis工作流程

1）通过Reader对象读取src目录下的mybatis.cfg.xml配置文件(该文本的位置和名字可任意)

2）通过SqlSessionFactoryBuilder对象创建SqlSessionFactory对象

3）从当前线程中获取SqlSession对象

4）事务开始，在mybatis中默认

5）通过SqlSession对象读取StudentMapper.xml映射文件中的操作编号，从而读取sql语句

6）事务提交，必写

7）关闭SqlSession对象，并且分开当前线程与SqlSession对象，让GC尽早回收

5基于MybatisUtil工具类，完成CURD操作

　　映射配置文件

     
         
              
               
               
           
          
      
               INSERT  INTO students(id,name, sal) VALUES(#{id},#{name},#{sal})    
          
          
              SELECT ID,NAME,SAL FROM students WHERE id = #{xxx}        
              SELECT ID,NAME,SAL FROM students        
      
               UPDATE students SET name=#{name},sal=#{sal} WHERE id=#{id}    
          
      
               DELETE  FROM students WHERE  ID=#{id}    
      
     

　　dao

public void add(Student student) throws Exception{        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            sqlSession.insert(Student.class.getName()+".add",student);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }    }    private Student findById(int id) {        Student student= null;        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            student = sqlSession.selectOne(Student.class.getName() + ".findById", id);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }        return student;    }    private List
     
       findAll() {        List
      
        students = new ArrayList<>();        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            students = sqlSession.selectList(Student.class.getName() + ".findAll");            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }        return students;    }    private void update(Student student) {        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            sqlSession.update(Student.class.getName()+".update",student);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }    }    private void delete(Student student) {        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            sqlSession.delete(Student.class.getName()+".delete",student);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }    }
      
     

6.分页查询(mysql,oracle)

　　映射配置文件

mysql

        SELECT id,name,sal FROM students LIMIT #{start},#{size}    

oracle

        SELECT ID,NAME,SAL        FROM (SELECT ROWNUM IDS,ID,NAME,SAL            FROM STUDENTS            WHERE ROWNUM < #{end})        WHERE IDS > #{start}    

　　dao

public List
     
       findAllWithFy(int start,int size){        List
      
        students = new ArrayList<>();        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            Map
       
         map = new LinkedHashMap<>();            map.put("start",start);            map.put("size",size);            students = sqlSession.selectList(Student.class.getName()+".findAllWithFy",map);            sqlSession.commit();            return students;        }catch (Exception e){            sqlSession.rollback();            throw e;        }finally {            MybatisUtil.closeSqlSession();        }    }
       
      
     

7.动态SQL操作之查询

　　映射配置文件

        SELECT ID,NAME,SAL FROM STUDENTS                                    and ID = #{pid}                                        and NAME = #{pname}                                        AND SAL < #{psal}                        

　　dao

public List
     
       findAll(Integer id ,String name,Double sal){        List
      
        students = new ArrayList<>();        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            Map
       
         map = new LinkedHashMap<>();            map.put("pid",id);            map.put("pname",name);            map.put("psal",sal);            students = sqlSession.selectList(Student.class.getName()+".findAll",map);            sqlSession.commit();            return students;        }catch (Exception e){            sqlSession.rollback();            throw new RuntimeException(e);        }finally {            MybatisUtil.closeSqlSession();        }    }
       
      
     

8.动态SQL操作之更新

　　映射配置文件

     
              UPDATE STUDENTS        
                  
       
                        name = #{pname},            
                   
       
                        sal = #{psal},            
               
              WHERE id = #{pid}    
     

　　dao

public void update(Student student){        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            Map
     
       map = new LinkedHashMap<>();            map.put("pid",student.getId());            map.put("pname",student.getName());            map.put("psal",student.getSal());            sqlSession.update(Student.class.getName()+".update",map);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw new RuntimeException(e);        }finally {            MybatisUtil.closeSqlSession();        }    }
     

9.动态SQL操作之删除

　　映射配置文件

     
              DELETE FROM  students WHERE ID IN        
      
                   #{ids}        
          
     

　　dao

public void deleteAll(int... ids)throws Exception{        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            sqlSession.delete(Student.class.getName()+".deleteAll",ids);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw new RuntimeException(e);        }finally {            MybatisUtil.closeSqlSession();        }    }

10.动态SQL操作之插入

　　映射配置文件

         
             
                  
       
                        id,            
                   
       
                        name,            
                   
       
                        sal,            
               
          
         
             
                  
       
                        #{id},            
                   
       
                        #{name},            
                   
       
                        #{sal},            
               
          
         
     
              INSERT INTO students(
      ) values (
      )    
     

　　dao

public void deleteList(List
     
       ids)throws Exception{        SqlSession sqlSession = null;        try {            sqlSession = MybatisUtil.getSqlSession();            sqlSession.delete(Student.class.getName()+".deleteList",ids);            sqlSession.commit();        }catch (Exception e){            sqlSession.rollback();            throw new RuntimeException(e);        }finally {            MybatisUtil.closeSqlSession();        }    }