项目场景：

使用mybatis来连接Oracle数据库查询数据

问题描述：

Exception in thread"main" org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: java.sql.SQLRecoverableException: IO 错误: The Network Adapter could not establish the connection
### The error may exist in com/test/dao/rj191Mapper.xml
### The error may involve?.selectRjList
### The error occurredwhile executing a query
### Cause: java.sql.SQLRecoverableException: IO 错误: The Network Adapter could not establish the connection
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:149)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:135)
	at com.test.MyApp3.main(MyApp3.java:20)
Caused by: java.sql.SQLRecoverableException: IO 错误: The Network Adapter could not establish the connection
	at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:673)
	at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:711)
	at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:385)
	at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:30)
	at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:558)
	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.executor.BaseExecutor.getConnection(BaseExecutor.java:336)
	at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:85)
	at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62)
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147)...3 more
Caused by: oracle.net.ns.NetException: The Network Adapter could not establish the connection
	at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:445)
	at oracle.net.resolver.AddrResolution.resolveAndExecute(AddrResolution.java:464)
	at oracle.net.ns.NSProtocol.establishConnection(NSProtocol.java:594)
	at oracle.net.ns.NSProtocol.connect(NSProtocol.java:229)
	at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1360)
	at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:486)...24 more
Caused by: java.net.ConnectException: Connection refused: connect
	at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
	at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)
	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 oracle.net.nt.TcpNTAdapter.connect(TcpNTAdapter.java:162)
	at oracle.net.nt.ConnOption.connect(ConnOption.java:133)
	at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:411)...29 more

原因分析：

The Network Adapter could not establish the connection
网络适配器无法建立连接，代表着我们Oracle服务未开启。

解决方案：

我们在连接Oracle数据库时候一定要打开所需的服务：

1. 通过 window+r 输入services.msc 打开我们的本地服务
2. 找到服务名称为：
   OracleServiceSID（这里SID是你的实例名）
   OracleOraDb11g_home1TNSListener（监听器服务）
   ———— 至少要启动这两种服务 ——————
3. 最后就可以查询到我们数据表中数据