009.初始化工具类MyBatisUtil

1.MyBatisUtils工具类,创建全局唯一的SqlSessionFactory对象（src/main/java/com/imooc/mybatis/utils/MyBatisUtils.java）

package com.imooc.mybatis.utils;

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 java.io.IOException;
import java.io.Reader;

/**
 * MyBatisUtils工具类,创建全局唯一的SqlSessionFactory对象
 */
public class MyBatisUtils {
    //利用static(静态)属于类不属于对象,且全局唯一
    private static SqlSessionFactory sqlSessionFactory = null;
    //利用静态块在初始化类时实例化sqlSessionFactory
    static {
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
            //初始化错误时,通过抛出异常ExceptionInInitializerError通知调用者
            throw new ExceptionInInitializerError(e);
        }
    }

    /**
     * openSession 创建一个新的SqlSession对象
     * @return SqlSession对象
     */
    public static SqlSession openSession(){
        return sqlSessionFactory.openSession();
    }

    /**
     * 释放一个有效的SqlSession对象
     * @param session 准备释放SqlSession对象
     */
    public static void closeSession(SqlSession session){
        if(session != null){
            session.close();
        }
    }
}

2.测试MyBatisUtils

/**
     * MyBatisUtils使用指南
     *
     * @throws Exception
     */
    @Test
    public void testMyBatisUtils() throws Exception
    {
        SqlSession sqlSession = null;
        try
        {
            sqlSession = MyBatisUtils.openSession();
            Connection connection = sqlSession.getConnection();
            System.out.println(connection);
        }
        catch (Exception e)
        {
            throw e;
        }
        finally
        {
            MyBatisUtils.closeSession(sqlSession);
        }
    }