java - SQL 数据库和 Java

Question

我在这里读了很多关于如何从 java 连接到 mysql 数据库的文章。不知何故，这对我不起作用，我无法找出我做错了什么。首先，这是我的代码:

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Connection;
import java.sql.DriverManager;

class sqltest{
    private static int uid = -1;
    protected static Connection dbConn = null;

    public static void main (String args[]){
        try {
            Class.forName("org.gjt.mm.mysql.Driver").newInstance();
        } catch (ClassNotFoundException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        ResultSet rs = null;
        try{
            dbConn = DriverManager.getConnection("jdbc:mysql://XXX.XXX.XX.XX:XXXX/peXXXXX","XXXXXX","XXXXXX");
            PreparedStatement ps = dbConn.prepareStatement("select id from supervisor where username = philipp");
            rs = ps.executeQuery();
            uid = rs.getInt("id");
        }catch(SQLException e){
                e.printStackTrace();
            }
        System.out.println(uid);
    }
}

连接详细信息(用户、密码、地址)正确。只有一件事我不明白:已经有一个 java-web-applet 正在建立这样的连接，并且它不使用端口(这可能吗？)。现在这些是我得到的错误:当我不使用端口或使用默认的 3306 端口时，我收到此错误:

com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception: 

** BEGIN NESTED EXCEPTION ** 

java.net.ConnectException
MESSAGE: Connection timed out: connect

STACKTRACE:

java.net.ConnectException: Connection timed out: 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:173)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:268)
    at com.mysql.jdbc.Connection.createNewIO(Connection.java:2745)
    at com.mysql.jdbc.Connection.<init>(Connection.java:1553)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at sqltest.main(sqltest.java:27)


** END NESTED EXCEPTION **



Last packet sent to the server was 28 ms ago.-1

    at com.mysql.jdbc.Connection.createNewIO(Connection.java:2820)
    at com.mysql.jdbc.Connection.<init>(Connection.java:1553)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at sqltest.main(sqltest.java:27)

我认为这是由错误的端口引起的。这是正确的吗？

当我使用我认为正确的端口时，我没有收到任何错误，但程序只是无休止地运行，不会产生任何结果。

感谢您的帮助!

Answer 1

确保您连接到正确的主机/端口并且这些主机/端口可以访问。
为此，例如打开终端并输入 telnet <host> <port>来自同一个
运行 Java 代码的机器。