本篇博客的主要内容是：（1）SqlSessionFactory的演示；（2）SqlSession的演示；（3）本篇博客的内容仅仅是演示这两个类的作用，本篇博客的案例，书写形式都不是实际工作中惯用的书写形式，即本篇博客的目的仅仅是让自己对这俩类有个基本了解。（4）本篇博客内容很简单，快速浏览效果更佳。
目录
一.SqlSessionFactory和SqlSession简介
二.演示案例
1.MyBatisTestor：案例代码
2.代码说明：
（1）代码的基本架构
（2）如果某个数据库连接不上，会报PersistenceException（了解这种情况，以后遇到了这种错误，知道解决的方向就行）
（3）注意Resources使用的是哪一个
（4）本案例的创建Connection仅仅出于演示目的
（5）和以前套路一样，创建连接放在try块中，关闭连接放在finally块中
一.SqlSessionFactory和SqlSession简介
二.演示案例
1.MyBatisTestor：案例代码
package com.imooc.mybatis;
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.Reader;
import java.sql.Connection;
/**
* JUnit单元测试类
*/
public class MyBatisTestor {
@Test
public void testSqlSessionFactory() {
try {
// get是获取；Resources代表资源，就是指文本文件；AsReader是按照字符流的方式读取；
// Resources.getResourceAsReader()方法会默认从当前编译后class文件路径下去加载这个xml文件；
Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
// 初始化SqlSessionFactory对象，同时解析mybatis-config.xml文件；
// SqlSessionFactoryBuilder使用了构造者模式，利用构造者模式初始化SqlSessionFactory对象；
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
System.out.println("SessionFactory加载成功。");
SqlSession sqlSession = null;
try {
// 创建SqlSession对象；SqlSession对象是专用于数据库交互的；
sqlSession = sqlSessionFactory.openSession();
Connection connection = sqlSession.getConnection();
System.out.println(connection);
}catch (Exception e){
e.printStackTrace();
}finally {
if (sqlSession != null) {
// 如果在mybatis-config.xml中的<dataSource type="POOLED">，代表使用连接池，close则是将连接回收到连接池中；
// 如果在mybatis-config.xml中的<dataSource type="UNPOOLED">，代表不使用连接池，close则是调用Connection.close()方法关闭；
sqlSession.close();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
2.代码说明：
（1）代码的基本架构
（2）如果某个数据库连接不上，会报PersistenceException（了解这种情况，以后遇到了这种错误，知道解决的方向就行）
其就报了PersistenceException
详细报错信息：随便瞅一眼就行。
org.apache.ibatis.exceptions.PersistenceException:
### Error getting a new connection. Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
at org.apache.ibatis.session.defaults.DefaultSqlSession.getConnection(DefaultSqlSession.java:299)
at com.imooc.mybatis.MyBatisTestor.testSqlSessionFactory(MyBatisTestor.java:29)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:342)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2197)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2230)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2025)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:778)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:208)
at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:201)
at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:196)
at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.getConnection(UnpooledDataSource.java:93)
at org.apache.ibatis.datasource.pooled.PooledDataSource.popConnection(PooledDataSource.java:403)
at org.apache.ibatis.datasource.pooled.PooledDataSource.getConnection(PooledDataSource.java:89)
at org.apache.ibatis.transaction.jdbc.JdbcTransaction.openConnection(JdbcTransaction.java:138)
at org.apache.ibatis.transaction.jdbc.JdbcTransaction.getConnection(JdbcTransaction.java:60)
at org.apache.ibatis.session.defaults.DefaultSqlSession.getConnection(DefaultSqlSession.java:297)
... 23 more
Caused by: java.net.ConnectException: Connection timed out: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:301)
... 45 more
Process finished with exit code -1
（3）注意Resources使用的是哪一个
（4）本案例的创建Connection仅仅出于演示目的
（5）和以前套路一样，为了保证close()方法一定将能够被执行，将创建连接放在try块中，关闭连接放在finally块中
