無法連接到MySQL數據庫

Question

每當我嘗試運行此rs私有服務器時，都會收到此控制台錯誤。 幾乎所有內容都連接到mysql數據庫。

我已經花了很長時間來解決這個問題，但無法弄清楚出了什么問題。 如果有任何特定文件，您可能需要查看以幫助我找出問題所在，請告訴我，我將其發布。

所有幫助將不勝感激！

[Stage - 1] Launching Elunity...
[Stage - 2] Loaded object configurations
[Stage - 3] Loaded region configurations
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1 432 637 479 787 milliseconds ago.  The last packet sent successfully to the   server was 0 milliseconds ago.
Failed to connect to MySQL database
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2214)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:773)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:352)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at paladious.model.players.Highscores.process(Highscores.java:17)
at paladious.Server.main(Server.java:117)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1 432 637 479 777 milliseconds ago.  The last packet sent successfully to the server was 0 milliseconds ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2137)
... 13 more
Caused by: java.net.ConnectException: Connection refused: 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 java.net.Socket.<init>(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:253)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:290)
... 14 more
[Stage - 4] Loaded single event manager
[Stage - 7] Loaded NPC drops
[Stage - 8] Loaded player punishments and starters
[Stage - 10] Elunity online on port :43594

提前致謝！ :)

Answer 1

這是一個包裝的異常，並不是很有趣。 這是異常的根本原因，實際上可以告訴我們一些有關根本原因的信息。 請在堆棧跟蹤中再看一些。 然后您將面臨一個SQLException：連接被拒絕或SQLException：連接超時的機會很大。

如果您的情況也是如此，那么所有可能的原因是：

1. JDBC URL中的IP地址或主機名錯誤。
2. 本地DNS服務器無法識別JDBC URL中的主機名。
3. JDBC URL中的端口號丟失或錯誤。
4. 數據庫服務器已關閉。
5. DB服務器不接受TCP / IP連接。
6. Java和DB之間的某種事物正在阻止連接，例如防火牆或代理。

要解決一個或兩個問題，請遵循以下建議：

1. 使用ping驗證並測試它們。
2. 刷新DNS或在JDBC URL中使用IP地址。
3. 根據MySQL DB的my.cnf進行驗證。
4. 啟動它。
5. 驗證是否在沒有--skip-networking選項的情況下啟動了mysqld。
6. 禁用防火牆和/或配置防火牆/代理以允許/轉發端口。