MySQL的JDBC连接问题

Question

最近两天，我一直在寻找StackOverflow来解决类似问题，并且发现很多人都遇到了同样的问题，但是，没有任何建议对我有用，所以我认为我会在此处发布确切的问题，以防万一我遗漏了一些东西明显。 我注意到连接被拒绝的原因，但是，我确切知道我的用户名和密码以及dbname是什么，所以我知道这不是身份验证问题。

沮丧之后，我发现了一个仅检查机器上运行的MySQL版本的类。 我也使用XAMPP运行MySQL。 但是，无论我尝试做什么，都会出现以下错误：

Apr 26, 2014 7:29:37 PM Version main
SEVERE: 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.
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: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:525)
    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:579)
    at java.sql.DriverManager.getConnection(DriverManager.java:221)
    at Version.main(Version.java:23)
Caused by: java.net.ConnectException: Connection refused
    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:258)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:306)
    ... 15 more

这是我的Version类：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Version {

    public static void main(String[] args) {

        Connection con = null;
        Statement st = null;
        ResultSet rs = null;

        String url = "jdbc:mysql://localhost:3306/dbname";
        String user = "username";
        String password = "password";

        try {
            con = DriverManager.getConnection(url, user, password);
            st = con.createStatement();
            rs = st.executeQuery("SELECT VERSION()");

            if (rs.next()) {
                System.out.println(rs.getString(1));
            }

        } catch (SQLException ex) {
            Logger lgr = Logger.getLogger(Version.class.getName());
            lgr.log(Level.SEVERE, ex.getMessage(), ex);

        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (st != null) {
                    st.close();
                }
                if (con != null) {
                    con.close();
                }

            } catch (SQLException ex) {
                Logger lgr = Logger.getLogger(Version.class.getName());
                lgr.log(Level.WARNING, ex.getMessage(), ex);
            }
        }
    }
}

Answer 1

我能够使它工作。

我必须重新安装XAMPP并从Exported SQL重新创建数据库。

你不知道我这样做有多烦。 很多浪费的时间。 谢谢您的帮助。

Answer 2

在Ubuntu上，我使用MySQL，并尝试使用终端编辑文件
须藤nano /etc/mysql/my.cnf
找到包含以下内容的行：
绑定地址
只需编辑此行
绑定地址= 0.0.0.0
保存文件并重新启动mysql
sudo服务mysql重新启动，然后重试

它对我有用，祝你好运！

Answer 3

您错过了一些代码朋友！ 尝试添加Class.forName(com.mysql.jdbc.Driver); 在您的try catch块中。 希望能帮助到你