Mybatis学习之道（一）

本例子为采用的mysql+maven+mybatis构建。

　　初步学习mybatis：

　　　　mybatis为一个半自动框架，相对于hibernate来说他更加轻巧，学习成本更低。

1.新建一个maven工程

2.在maven中配置依赖jar包

   <dependencies>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
       <version>4.11</version>
       <scope>test</scope>
     </dependency>
       <dependency>
           <groupId>org.mybatis</groupId>
           <artifactId>mybatis</artifactId>
           <version>3.4.1</version>
       </dependency>
       <dependency>
           <groupId>mysql</groupId>
           <artifactId>mysql-connector-java</artifactId>
           <version>5.1.40</version>
       </dependency>
   </dependencies>

3.新建一个jdbc.properties文件

jdbc.driver=org.gjt.mm.mysql.Driver jdbc.url=jdbc:mysql://localhost:3306/mybatisStudy jdbc.username=root jdbc.password=123456

4.创建mybatis配置文件

　　propertis:导入配置文件

　　

 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE configuration
         PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
         "http://mybatis.org/dtd/mybatis-3-config.dtd">
 <configuration>
     <properties resource="jdbc.properties"></properties>
     <!--设置一些配置信息-->
     <settings>
         <setting name="useGeneratedKeys" value="true"/>
     </settings>
     <!--设置别名-->
     <typeAliases>
         <typeAlias type="cn.lonecloud.d1.model.Blog" alias="Blog"></typeAlias>
     </typeAliases>
     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC"/>
             <dataSource type="POOLED">
                 <property name="driver" value="${jdbc.driver}"/>
                 <property name="url" value="${jdbc.url}"/>
                 <property name="username" value="${jdbc.username}"/>
                 <property name="password" value="${jdbc.password}"/>
             </dataSource>
         </environment>
     </environments>
     <!--mapper对应的文件-->
     <mappers>
         <mapper resource="mapper/BlogMapper.xml"></mapper>
     </mappers>
 </configuration>

5创建数据库

　　

 SET NAMES utf8;
 SET FOREIGN_KEY_CHECKS = 0;

 -- ----------------------------
 --  Table structure for `blog`
 -- ----------------------------
 DROP TABLE IF EXISTS `blog`;
 CREATE TABLE `blog` (
   `id` varchar(32) NOT NULL DEFAULT '',
   `name` varchar(255) DEFAULT '',
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

 SET FOREIGN_KEY_CHECKS = 1;

6.创建POJO类

 package cn.lonecloud.d1.model;

 /**
  * Created by lonecloud on 17/3/17.
  */
 public class Blog {
     private String id;

     private String name;

     public String getId() {
         return id;
     }

     @Override
     public String toString() {
         return "Blog{" +
                 "id='" + id + '\'' +
                 ", name='" + name + '\'' +
                 '}';
     }

     public void setId(String id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }
 }

.7创建对应的接口类

　　由于mybatis是接口式编程，会将对应的接口通过映射的方式在其容器中通过代理方式创建出一个对象，所以不需要创建实现类

 package cn.lonecloud.d1.dao;

 import cn.lonecloud.d1.model.Blog;

 /**
  * Created by lonecloud on 17/3/17.
  * mybatis接口式编程
  */
 public interface BlogMapper {
     Blog selectOne(String id);
 }

8.编写对应的mapper文件

　　namespce:命名空间,为对这个mapper文件进行唯一性标示，最好使用对应的接口全类名

　　select:筛选语句相当于说明这是一个select查询 id标明为该类下面的某个方法，

　　resultType:返回数据类型，

　　#{id}:为传递过来的参数，最好是和参数名相同

 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE mapper
         PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
         "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 <mapper namespace="cn.lonecloud.d1.dao.BlogMapper">
     <select id="selectOne" resultType="Blog">
         select * from Blog where id = #{id}
     </select>
 </mapper>

9.编写测试类：

 package cn.lonecloud.d1;

 import cn.lonecloud.d1.dao.BlogMapper;
 import cn.lonecloud.d1.model.Blog;
 import org.apache.ibatis.io.Resources;
 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 import org.junit.Test;

 import java.io.IOException;
 import java.io.InputStream;

 /**
  * Created by lonecloud on 17/3/17.
  */
 public class SessionTest {

     SqlSessionFactory sqlSessionFactory;
     @Test
     public void session() throws IOException {
         String resource = "mybatis-config.xml";//配置文件
         InputStream inputStream = Resources.getResourceAsStream(resource);//读取配置文件
         sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//获取sqlSession 对象
         System.out.println(sqlSessionFactory);
         SqlSession session = sqlSessionFactory.openSession();//打开session
         try{
             BlogMapper blogMapper = session.getMapper(BlogMapper.class);
             Blog blog = blogMapper.selectOne("sasa");
             System.out.println(blog);
         }finally {
             session.close();
         }
     }
 }

注意的是SqlSession位非线程安全的类，这个如果定义为类变量会导致线程安全性问题！！

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