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似乎有足够的与CommunicationsException有关的问题发布在Stackoverflow上。但他们没有一个能够帮助我摆脱困境。MariaDB CommunicationsException：通信链接失败
我在CentOS的7服务器上安装MariaDB的5.5，并且配置的一切，让我可以远程通过MySQL工作台或数据源资源管理器在eclipse连接到数据库服务器。成功连接的屏幕截图如下所示。 
但是，当我尝试通过JDBC连接数据库服务器时，它继续失败，异常“com.mysql.jdbc.exceptions.jdbc4.CommunicationsException：通信链接失败”。
测试类如下所示。
package com.pratice;
import java.sql.*;
public class DatabaseConn {
public static void main(String[] args) throws Exception{
Connection conn = null;
ResultSet rs = null;
Statement stmt = null;
String url = "jdbc:mysql://59.12.140.121:6330/myPrjs";//?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true
String username = "user";
String password = "password";
String driver = "com.mysql.jdbc.Driver";
try{
Class.forName(driver);
conn = DriverManager.getConnection(url, username, password);
stmt = conn.createStatement();
rs = stmt.executeQuery("SELECT 1");
while(rs.next()){
System.out.print(rs.getObject(1) + "\t" + rs.getObject(2));
}
}finally{
if(rs!=null) {
rs.close();
}
if(stmt!=null) {
stmt.close();
}
if (conn != null) {
conn.close();
}
}
}
}
当我运行DatabaseConn时，我收到了错误消息。
Exception in thread "main" 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:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1127)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:356)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2502)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2539)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2321)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:832)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:417)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:344)
at java.sql.DriverManager.getConnection(DriverManager.java:571)
at java.sql.DriverManager.getConnection(DriverManager.java:215)
at com.webjsp.pratice.DatabaseConn.main(DatabaseConn.java:18)
Caused by: java.net.SocketException: Bad address: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:579)
at java.net.Socket.connect(Socket.java:528)
at java.net.Socket.<init>(Socket.java:425)
at java.net.Socket.<init>(Socket.java:241)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:258)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:306)
... 15 more
我解决不了这个问题，所以我在互联网上搜索，我发现了一个清单，在here。但现在我可以通过IDE连接到我的数据库服务器，我不知道可能是错误的。
我也试过，而不是使用MySQL驱动org.mariadb.jdbc.driver，我得到错误信息了。
Exception in thread "main" java.sql.SQLNonTransientConnectionException: Could not connect to 59.12.140.121:6330 : Bad address: connect
at org.mariadb.jdbc.internal.SQLExceptionMapper.get(SQLExceptionMapper.java:136)
at org.mariadb.jdbc.internal.SQLExceptionMapper.throwException(SQLExceptionMapper.java:106)
at org.mariadb.jdbc.Driver.connect(Driver.java:115)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at DatabaseConn.main(DatabaseConn.java:16)
Caused by: org.mariadb.jdbc.internal.common.QueryException: Could not connect to 59.12.140.121:6330
: Bad address: connect
at org.mariadb.jdbc.internal.mysql.MySQLProtocol.connect(MySQLProtocol.java:714)
at org.mariadb.jdbc.internal.mysql.MySQLProtocol.<init>(MySQLProtocol.java:280)
at org.mariadb.jdbc.Driver.connect(Driver.java:111)
... 3 more
Caused by: java.net.SocketException: Bad address: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at org.mariadb.jdbc.internal.mysql.MySQLProtocol.connect(MySQLProtocol.java:387)
at org.mariadb.jdbc.internal.mysql.MySQLProtocol.connect(MySQLProtocol.java:709)
... 5 more
谁能告诉我我该怎么解决这个问题，或者给我一些暗示，为什么会发生？非常感谢。
防火墙问题？ – gustafbstrom
@gustafbstrom我想不是。我配置了防火墙设置，并通过MySQL Workbench远程连接到我的数据库服务器。 – sincosmos