Mybatis

1. jdbc
   
   

   package com.gcl.jdbc;
   
   import java.sql.Connection;
   import java.sql.DriverManager;
   import java.sql.PreparedStatement;
   import java.sql.ResultSet;
   
   public class JDBCTest {
       public static void main(String[] args) throws Exception {
           String url="jdbc:mysql://localhost:3306/mybatis_study";
           String user="root";
           String password="root";
           String sql = "select * from user where username=?;";
           //加载驱动    
           Class.forName("com.mysql.jdbc.Driver");
           //获取连接
           Connection conn = DriverManager.getConnection(url, user, password);
           //获取预处理statement
           PreparedStatement pst = conn.prepareStatement(sql);
           //设置参数
           pst.setString(1, "张三丰");
           //获得查询结果集
           ResultSet ret = pst.executeQuery();
           //遍历结果集
           while(ret.next()){
               System.out.println(ret.getString("username"));
           }
           ret.close();
           pst.close();
           conn.close();
       }
   
   }

   问题：开启关闭连接，造成数据库资源浪费，降低性能；SQL硬编码到代码中，不利于维护

2. Mybatis入门程序
   添加jar包
   
   

   
   SqlMapConfig.xml是Mybatis核心配置文件，在里面配置数据源等，在里面还加入了编写有sql语句的User.xml文件
   配置log4j使sql语句打印到控制台：加入log4j和slf4j的包，然后在log4j.properties中
   
   

   # Global logging configuration
   #开发环境日志级别DEBUG 生产环境INFO或error
   log4j.rootLogger=DEBUG, stdout
   # Console output...
   log4j.appender.stdout=org.apache.log4j.ConsoleAppender
   log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
   log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
   #log4j.logger.org.apache=INFO

   测试代码：
   
   

   package com.gcl.test;
   
   import java.io.InputStream;
   
   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 com.gcl.po.User;
   
   public class TSET {
   
       @Test
       public void test() throws Exception {
           String resource = "mybatis/SqlMapConfig.xml";
           InputStream is = Resources.getResourceAsStream(resource);
           SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder()
                   .build(is);
           SqlSession sqlsession = sqlSessionFactory.openSession();
           User user = sqlsession.selectOne("test.getUserbyid", 10);
           System.out.println(user.getAddress());
           sqlsession.close();
       }
   
   }