我通过指定数据库（jdbc:mysql://hostname:port/db）连接到mysql服务器，或者在所有网络中使用DataGrip指定数据库（jdbc:mysql://hostname:port/）。
当我在学校网络中时，我仍然可以在不指定数据库的情况下连接到mysql服务器，或者指定除X数据库之外的数据库。如果我指定像jdbc:mysql://hostname:port/X这样的X数据库，请执行以下错误：
[08S01] Communications link failure.
The last packet successfully received from the server was 8 milliseconds ago. The last packet sent successfully to the server was 8 milliseconds ago.
我尝试连接指定超时变量，我没有得到任何结果。 任何人都建议我解决这个问题的正确方法。
完全异常堆栈跟踪：
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 200 milliseconds ago. The last packet sent successfully to the server was 24 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:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3589)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3478)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4019)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:951)
at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1717)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1276)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2395)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2428)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2213)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:797)
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:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:389)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:305)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at Example.main(Example.java:22)
Caused by: java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:210)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:114)
at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:161)
at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:189)
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3036)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3489)
... 20 more