MariaDB CommunicationsException：通信 link 失败
MariaDB CommunicationsException: Communications link failure
在 Whosebug 上发布的与 CommunicationsException 相关的问题似乎已经够多了。但是 none 帮助我摆脱了困境。
我在我的 CentOS 7 服务器上安装了 MariaDB 5.5，并配置了所有内容，以便我可以通过 MySQL Workbench 或 Eclipse 中的数据源资源管理器远程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，它继续失败并出现异常 "com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure"。
测试class如下图
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
我无法解决这个问题，所以我在网上搜索，在 here 找到了一个检查表。但是现在我可以通过 IDE 连接到我的数据库服务器，我不知道哪里出了问题。
我也尝试使用 org.mariadb.jdbc.driver 而不是 mysql 驱动程序，我也收到错误消息。
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
谁能告诉我如何解决这个问题，或者给我一些提示，说明为什么会这样？非常感谢。
解决问题的关键点在"java.net.SocketException: Bad address: connect"。
问题是由客户端（我的 Windows PC）的防火墙规则引起的。我在客户端 PC 上启用了 Ahnlab V3 Internet Security Personal Firewall。默认情况下，出站规则仅允许某些类型的传出套接字。当我尝试使用 workbench 连接到我的远程服务器时，没有问题。但是当我尝试通过 运行 java Class 连接到服务器时，本地防火墙保留了套接字，所以连接请求甚至没有通过我的网卡！我添加了一个新的出站规则，允许 mysql 出站连接，然后我的程序运行正常。
希望这对遇到同样问题的人有所帮助。
在 Whosebug 上发布的与 CommunicationsException 相关的问题似乎已经够多了。但是 none 帮助我摆脱了困境。
我在我的 CentOS 7 服务器上安装了 MariaDB 5.5，并配置了所有内容，以便我可以通过 MySQL Workbench 或 Eclipse 中的数据源资源管理器远程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，它继续失败并出现异常 "com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure"。
测试class如下图
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
我无法解决这个问题，所以我在网上搜索，在 here 找到了一个检查表。但是现在我可以通过 IDE 连接到我的数据库服务器，我不知道哪里出了问题。
我也尝试使用 org.mariadb.jdbc.driver 而不是 mysql 驱动程序，我也收到错误消息。
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
谁能告诉我如何解决这个问题，或者给我一些提示，说明为什么会这样？非常感谢。
解决问题的关键点在"java.net.SocketException: Bad address: connect"。
问题是由客户端（我的 Windows PC）的防火墙规则引起的。我在客户端 PC 上启用了 Ahnlab V3 Internet Security Personal Firewall。默认情况下，出站规则仅允许某些类型的传出套接字。当我尝试使用 workbench 连接到我的远程服务器时，没有问题。但是当我尝试通过 运行 java Class 连接到服务器时，本地防火墙保留了套接字，所以连接请求甚至没有通过我的网卡！我添加了一个新的出站规则，允许 mysql 出站连接，然后我的程序运行正常。
希望这对遇到同样问题的人有所帮助。