mybatis 开发自己的项目

1、Mybatis优缺点

优点：  Mybatis实现了对Dao层的封装，隔离了SQL语句，便于管理，避免了像JDBC那样操作数据集，便于扩展等等。

缺点：  Mybatis属于?半自动“ORM”，比Hibernate的工作做得要多很多，对象参数传递比较麻烦，没有Hibernate对象操作的概念。

2、Mybatis的实现方式  

Mybatis提供两种应用实现：XML配置和注解。

2.1配置主要依赖实体对象的xml文件，将对象以<resultMap>形式注入，并提供给<insert > <delete > <select> <update> 语句引用。

2.2使用注解来的比配置XML文件要简单得多。只需要在接口上添加相应的注解并附上SQL语句就行了，如：   

  插入语句：@insert(" insert  into table_user ..")   

  修改语句： @update(" update table_user set ....")  

  删除语句：@delete(" delete from table_user .....")   

  查询语句：@select(" select * from table_user .....")

3、下载mybatis的jar包：mybatis-3.1.1-bundle.zip?，网址：http://code.google.com/p/mybatis/

4、构建自己的mybatis项目,如图所示：

5、mybatis-config.xml:配置数据源和隐射文件

<?xml version="1.0" encoding="UTF-8" ?>

  <!DOCTYPE configuration   PUBLIC "-//ibatis.apache.org//DTD Config 3.0//EN"   "http://ibatis.apache.org/dtd/ibatis-3-config.dtd">

  <configuration>  

  <environments default="environment">      

    <environment id="environment">      

      <transactionManager type="JDBC"/>        

      <dataSource type="POOLED">         

          <property name="driver" value="com.mysql.jdbc.Driver"/>         

         <property name="url"   value="jdbc:mysql://localhost:3306/mybatis?characterEncoding =UTF-8"/>    

          <property name="username" value="root"/>       

          <property name="password" value="root"/>        

        </dataSource>    

      </environment>  

  </environments>  

<!--  <mappers>      

   <mapper resource="mybatis/User.xml"/>  

   </mappers>  -->

</configuration>

注：mappers部分字体是使用实体配置的实现，如果使用注解则不需要添加。

6、使用注解实现CRUD操作-此处以实现用户管理为例  

6.1编写接口（interface）：实际上就是官方文档所述的Mapper

public interface UserService {

   @Insert(" insert into users (id,username,password) values (#{id},#{username},#{password})") void add(@Param("id")String id,@Param("username") String username,@Param("password")String password); 

   @Delete(" delete  from users where id=#{id}") void delete(String id); 

   @Update(" update users set username=#{username},password=#{password} where id=#{id}") int update(@Param("username") String username,@Param("password")String password,@Param("id")String id); 

   @Select(" select * from users where id=#{id}")  User getUser(String id); 

   @Select(" select * from users order by id asc ")  List<User> getUsers();   @Select(" select * from users order by id asc limit #{pageSize} offset #{offset} ")  List<User> getUsersByPage(@Param("offset")int offset,@Param("pageSize") int pageSize);//offset=pageSize*(page-1)}?

注：使用注解时接口的方法不能重载，否者会产生Mapped Statements collection does not contain value for  异常,另外还应尽量避免配置和注解混合使用的情况。

6.2获取数据源

public class GetSqlSessionFactory {  

     private  static SqlSessionFactory sqlSessionFactory = null;   

     private static GetSqlSessionFactory getSqlSessionFactory = null; 

     private GetSqlSessionFactory(){         

          String rs = "mybatis-config.xml";   

          Reader reader = null;      

          try {              

              reader = Resources.getResourceAsReader(rs);    

          } catch (IOException e) {     

               e.printStackTrace();       

          }          

          sqlSessionFactory = new  SqlSessionFactoryBuilder().build(reader);   

          //注解方式查询时需要注册mapper  

           sqlSessionFactory.getConfiguration().addMapper(UserService.class); 

     }  

    public static GetSqlSessionFactory getInstance(){  

       if(getSqlSessionFactory == null)          getSqlSessionFactory = new GetSqlSessionFactory();        

       return getSqlSessionFactory;    

    }       

    public static SqlSessionFactory getSqlSessionFactory(){      

        return sqlSessionFactory;   

    }

}

6.3DAO层：数据访问

public class UserDao { 

  @SuppressWarnings("static-access") 

   public void add(String id,String username,String password) {  

       SqlSession session =GetSqlSessionFactory.getInstance().getSqlSessionFactory().openSession(); 

       try {      

          session.getMapper(UserService.class).add(id,username,password);     

          session.commit();//提交事务

        } catch (Exception e) { 

           e.printStackTrace(); 

       }finally{  

          session.close(); 

      }

   }   

 

   @SuppressWarnings("static-access") 

   public void delete(String id) {   

       SqlSession session=GetSqlSessionFactory.getInstance().getSqlSessionFactory().openSession(); 

       try {      

            session.getMapper(UserService.class).delete(id);    

            session.commit();//提交事务  

      } catch (Exception e) {  

           e.printStackTrace();

       }finally{   

        session.close(); 

      } 

  }

  @SuppressWarnings("static-access") 

   public int update(String username,String password,String id) { 

       int count=0;  

      SqlSession session=GetSqlSessionFactory.getInstance().getSqlSessionFactory().openSession();  

      try {  

          // Map<String, Object> map=new HashMap<String, Object>();    

          // map.put("username", user.getUsername());  

          // map.put("password", user.getPassword()); 

          // session.update("updateUser", map);  

          count=session.getMapper(UserService.class).update(username,password,id); 

           session.commit();//提交事务

       } catch (Exception e) {

            count=0;  

          e.printStackTrace();  

     }finally{

            session.close();

       }  

    return count;

  }

 @SuppressWarnings("static-access")

   public List<User> getUsers(int offset, int pageSize) {  

       List<User> users=new ArrayList<User>(); 

       SqlSession session =GetSqlSessionFactory.getInstance().getSqlSessionFactory().openSession(); 

       try { 

             //users=session.selectList("user_list_page", new User(),new  RowBounds(offset,pageSize));//未测试过 

             //注解方式查询    

             users=session.getMapper(UserService.class).getUsersByPage(offset, pageSize);

        } catch (Exception e) {

             e.printStackTrace();

        }finally{  

           session.close(); 

       }    

    return users; 

  }

}

6.4servlet实现数据跳转访问

protected void doPost(HttpServletRequest request, HttpServletResponse response)

     throws ServletException, IOException {

     response.setContentType("text/html;charset=utf-8");

     UserService userService=new UserServiceImpl(); 

    PrintWriter out = response.getWriter();

    String method=request.getParameter("method");

    String returnString=""; 

    //方法入口  

   if(method.equals("users")){  

     returnString=new  JsonUtil<User>().getJsonByListObj(userService.getUsers()); 

  }else if(method.equals("user")){ 

     String id=request.getParameter("id");

    returnString=new  JsonUtil<User>().getJsonByEntity(userService.getUser(id)); 

  }else if(method.equals("delete")){  

     String id=request.getParameter("id");   

     Map<String,Object> map=new HashMap<String, Object>();  

     map.put("event", method);   

     map.put("param", id); 

     returnString=new  JsonUtil<User>().getJsonByObject(map); 

  }else if(method.equals("update")){   

     String id=request.getParameter("id");  

     String username=request.getParameter("username");   

     String password=request.getParameter("password");  

     Map<String,Object> map=new HashMap<String, Object>();

     int count=userService.update(username, password,id);   

     map.put("status",count==0?false:true); 

     map.put("event", method);   

     map.put("param", id);  

     returnString=new  JsonUtil<User>().getJsonByObject(map); 

  }else if(method.equals("paginate")){ 

     int limit=Integer.valueOf(request.getParameter("pageSize"));  

     int offset=Integer.valueOf(request.getParameter("offset"));   

     returnString=new  JsonUtil<User>().getJsonByListObj(userService.getUsersByPage(offset, limit));

  }

//输出JSON数据  

out.print(returnString);  

out.flush();

out.close();

}

至此，注解方式的实现就全部完成了。

7、XML实体对象配置

<?xml version="1.0" encoding="UTF-8" ?> 

<!DOCTYPE mapper   PUBLIC "-//ibatis.apache.org//DTD Mapper 3.0//EN"   "http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">  

  <mapper namespace="com.boonya.mybatis.entity.User">   

    <resultMap id="UserResultMap"  type="com.boonya.mybatis.entity.User">    

       <result property="id" column="id" jdbcType="VARCHAR"  javaType="string"/>      

       <result property="name" column="name" javaType = "string"  jdbcType="VARCHAR"/>    

      <result property="createtime" column="createtime" javaType =  "string" jdbcType="VARCHAR"/>

      <result property="tilepath" column="tilepath" javaType =  "string" jdbcType="VARCHAR"/>      

      <result property="lastlogintime" column="lastlogintime"  javaType = "string" jdbcType="VARCHAR"/>    

      <result property="nickname" column="nickname" javaType =  "string" jdbcType="VARCHAR"/>   

     <result property="password" column="password" javaType =  "string" jdbcType="VARCHAR"/> 

     <result property="picture" column="picture" javaType = "string"  jdbcType="VARCHAR"/> 

     <result property="sex" column="sex" javaType = "string"  jdbcType="VARCHAR"/> 

     <result property="username" column="username" javaType =  "string" jdbcType="VARCHAR"/> 

    </resultMap>

 <!-- 一般的SQL查询或操作语句配置-->

<select id="user" parameterType="int" resultType="com.boonya.mybatis.entity.User" 

                           resultMap="UserResultMap">select * from users where id=#{id} </select>   

  <select id="users"   resultMap="UserResultMap">select * from users order by id asc </select>  

   <insert id="addUser" parameterType="com.boonya.mybatis.entity.User" parameterMap="UserResultMap">insert into users (id,name,createtime,email,tilepath,lastloginip,lastlogintime,nickname,password,picture,sessionid,sex,tel,username)   values (#{id},#{name},#{createtime},#{email},#{tilepath},#{lastloginip},#{lastlogintime},#{nickname},#{password},#{picture},#{sessionid},#{sex},#{tel},#{username})</insert>   

  <!-- Dynamic SQL 这里的方法未经测试 -->  

   <!-- IF -->  

   <select id="dynamic_user"   resultMap="UserResultMap">select * from users where username=#{username}    

     <if test="name!=null">and name=#{name}</if>  

   </select>      

    <!-- FOREACH -->    

  <select id="dynamic_users"   resultMap="UserResultMap">select * from users name=#{name} and createtime in     

    <foreach collection="list" item="classTimeList"  open="(" separator="," close=")">              #{classTimeList}           </foreach>   

    </select> 

<!-- choose when  otherwise-->    

<select id="dynamic_findNameLike"  resultMap="UserResultMap">         SELECT * FROM USERS WHERE NAME IS NOT NULL  

    <choose> 

        <when test="nickname!=null">AND nickname like #{nickname}</when>   

      <when test="picture!=null ">AND picture like #{picture}</when>   

      <otherwise>AND lastlogintime > #{lastlogintime}</otherwise>  

   </choose>

 </select>     

    <!-- WHERE -->   

<select id="dynamic_findUSERSLike" resultMap="UserResultMap">select * from users  

   <where>   

    <if test="name!=null">WHERE name LIKE #{name}</if>  

   </where> 

  </select>   

</mapper>

注：如果使用配置需将mybatis-config.xml文件的mapper去掉注释：

<!--  <mappers>      

     <mapper resource="mybatis/User.xml"/>   

    </mappers>  -->

并且注释掉使用注解的mapper隐射：  

  //注解方式查询时需要注册mapper   

  sqlSessionFactory.getConfiguration().addMapper(UserService.class);

配置方式是根据SQL语句的隐射去访问的 如UserDao 中的getUsers方法：  

  //xml方式查询 

  //users=session.selectList("users");

注：刚开始学习mybatis的使用很多地方或细节不是很在意，如某些地方存在问题希望指点一二！