跟着狂神學mybatis 建立第一個程序就遇到了一直解決不了的問題。。。不停百度查找，也一直沒解決問題，今天終於在csdn找到了解決方法
參考鏈接：https://blog.csdn.net/zks_1998/article/details/103327519?spm=1001.2014.3001.5501
遇到的問題：
**org.apache.ibatis.exceptions.PersistenceException: **
### Error querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 513 milliseconds ago. The last packet sent successfully to the server was 509 milliseconds ago.
### The error may exist in com/young/dao/UserMapper.xml
### The error may involve com.young.dao.UserDao.getUserList
### The error occurred while executing a query
### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 525 milliseconds ago. The last packet sent successfully to the server was 521 milliseconds ago.
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.binding.MapperMethod.executeForMany(MapperMethod.java:147)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:80)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:57)
at com.sun.proxy.$Proxy4.getUserList(Unknown Source)
at com.young.dao.UserDaoTest.test(UserDaoTest.java:16)
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$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 525 milliseconds ago. The last packet sent successfully to the server was 521 milliseconds ago.
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.ExportControlled.transformSocketToSSLSocket(ExportControlled.java:201)
at com.mysql.jdbc.MysqlIO.negotiateSSLConnection(MysqlIO.java:4914)
at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1663)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1224)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2199)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2230)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2025)
at com.mysql.jdbc.ConnectionImpl.
at com.mysql.jdbc.JDBC4Connection.
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:221)
at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:216)
at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.getConnection(UnpooledDataSource.java:95)
at org.apache.ibatis.datasource.pooled.PooledDataSource.popConnection(PooledDataSource.java:422)
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)
... 28 more
Caused by: javax.net.ssl.SSLHandshakeException: java.security.cert.CertificateException: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors
at sun.security.ssl.Alert.createSSLException(Alert.java:131)
at sun.security.ssl.TransportContext.fatal(TransportContext.java:353)
at sun.security.ssl.TransportContext.fatal(TransportContext.java:296)
at sun.security.ssl.TransportContext.fatal(TransportContext.java:291)
at sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:652)
at sun.security.ssl.CertificateMessage$T12CertificateConsumer.onCertificate(CertificateMessage.java:471)
at sun.security.ssl.CertificateMessage$T12CertificateConsumer.consume(CertificateMessage.java:367)
at sun.security.ssl.SSLHandshake.consume(SSLHandshake.java:376)
at sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:444)
at sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:422)
at sun.security.ssl.TransportContext.dispatch(TransportContext.java:183)
at sun.security.ssl.SSLTransport.decode(SSLTransport.java:154)
at sun.security.ssl.SSLSocketImpl.decode(SSLSocketImpl.java:1279)
at sun.security.ssl.SSLSocketImpl.readHandshakeRecord(SSLSocketImpl.java:1188)
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:401)
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:373)
at com.mysql.jdbc.ExportControlled.transformSocketToSSLSocket(ExportControlled.java:186)
... 60 more
Caused by: java.security.cert.CertificateException: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors
at com.mysql.jdbc.ExportControlled$X509TrustManagerWrapper.checkServerTrusted(ExportControlled.java:302)
at sun.security.ssl.AbstractTrustManagerWrapper.checkServerTrusted(SSLContextImpl.java:1255)
at sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:636)
... 72 more
Caused by: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors
at sun.security.provider.certpath.PKIXCertPathValidator.validate(PKIXCertPathValidator.java:159)
at sun.security.provider.certpath.PKIXCertPathValidator.engineValidate(PKIXCertPathValidator.java:85)
at java.security.cert.CertPathValidator.validate(CertPathValidator.java:292)
at com.mysql.jdbc.ExportControlled$X509TrustManagerWrapper.checkServerTrusted(ExportControlled.java:295)
... 74 more
Process finished with exit code -1
Mybaitis核心配置文件mybatis-config.xml 中的數據庫url的value只保留這一部分<propertyname="url"value="jdbc:mysql://localhost:3306/mybatis?>
然后就可以顯示數據庫的數據了!!!可是它還是有一個警告:
**Mon Apr 19 14:39:39 CST 2021 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification. **
翻譯：不建議在沒有服務器身份驗證的情況下建立SSL連接。根據MySQL 5.5.45+、5.6.26+和5.7.6+的要求，如果不設置顯式選項，則必須建立默認的SSL連接。需要通過設置useSSL=false來顯式禁用SSL，或者設置useSSL=true並為服務器證書驗證提供信任存儲。
出現這個警告的原因：mysql在高版本中需要指明是否進行SSL連接
解決方案如下：
在mysql連接字符串url中加入ssl=true或者false即可，如下所示。
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&userUnicode=true&characterEncoding=UTF-8"/>
SSL協議提供服務主要：
1）認證用戶服務器，確保數據發送到正確的服務器； .
2）加密數據，防止數據傳輸途中被竊取使用；
3）維護數據完整性，驗證數據在傳輸過程中是否丟失；
當前支持SSL協議兩層：
SSL記錄協議（SSL Record Protocol）：建立靠傳輸協議（TCP）高層協議提供數據封裝、壓縮、加密等基本功能支持
SSL握手協議（SSL Handshake Protocol）：建立SSL記錄協議用於實際數據傳輸始前通訊雙進行身份認證、協商加密
算法、 交換加密密鑰等。
所以建議設置useSSL為false，有時遇到的問題可以這樣來考慮