我正在使用tomcat创建一个vaadin Web应用程序,并在另一台服务器上创建一个外部数据库。无论如何,我都无法连接到外部数据库。我甚至使用j2se jre 1.6创建了一个新的纯java项目,并尝试连接到数据库,但连接仍然失败。我下载了mysql驱动程序并将其复制到〜/ Library / Java / Extensions中,甚至从构建路径中添加/删除,但仍然没有改变。 我关闭了防火墙,我不知道还能做什么。我相信我的代码是正确的,但无论如何:
String host = "jdbc:mysql://db.host.sk:3306/myDB";
String name = "name";
String pass = "pass";
Connection connection;
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
System.out.println("Connecting to database...");
connection = DriverManager.getConnection(host, name,
pass);
System.out.println("SUCCESSFUL!!!");
} catch (SQLException e) {
System.out.println("Connecting to database failed");
System.out.println(e.getMessage());
e.printStackTrace();
}
catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
你可以帮我解决这个问题吗?谢谢。
修改
堆栈跟踪:
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:525)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1121)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:355)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2479)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2516)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2301)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
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:525)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:317)
at java.sql.DriverManager.getConnection(DriverManager.java:579)
at java.sql.DriverManager.getConnection(DriverManager.java:221)
at DatabaseHelper.main(DatabaseHelper.java:17)
Caused by: java.net.ConnectException: Operation timed out
at java.net.PlainSocketImpl.socketConnect(Native Method)
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.SocksSocketImpl.connect(SocksSocketImpl.java:391)
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:259)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:305)
... 15 more
答案 0 :(得分:1)
检查您的数据库服务已在专用服务器上启动并运行。
答案 1 :(得分:0)
之前从未遇到过这种情况,我读了几篇文章,发现可能的原因可能是Java和数据库之间存在阻塞连接的问题,例如:防火墙或服务器已关闭/不支持tcp / ip 或主机名在jdbc url中无法被本地dns服务器等识别。 那么你可以尝试以下建议(值得一试):
SET GLOBAL wait_timeout = 10000;
您还可以在此处查看由 Soheil 发布的具有良好答案的类似问题:Solving a "communications link failure" with JDBC and MySQL
答案 2 :(得分:0)