无法从Ubuntu上的Java程序连接到localhost上的MySQL

Posted 2021-05-06

以下是代码。

import java.sql.*;

public class ActivityReader {
    public static void main(String[] args) {
                      System.out.println("mysql Connect Example.");
              Connection conn = null;
              String url = "jdbc:mysql://localhost:3306/";
              String dbName = "jdbctutorial";
              String driver = "com.mysql.jdbc.Driver";
              String userName = "root"; 
              String password = "password";
              try {
                  Class.forName("com.mysql.jdbc.Driver").newInstance();
                  conn = DriverManager.getConnection(url,userName,password);
                  System.out.println("Connected to the database");
                  conn.close();
                  System.out.println("Disconnected from database");
              } catch (Exception e) {
                      e.printStackTrace();
              }
    }

} 

我已经在this url的项目中添加了mysql-connector-java-5.1.20-bin.jar。 Mysql服务已经在运行。

mysql start/running, process 25326

MySQL Connect示例。

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:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:348)
    at c

om.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2391)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2428)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2213)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:797)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:389)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:305)
    at java.sql.DriverManager.getConnection(DriverManager.java:582)
    at java.sql.DriverManager.getConnection(DriverManager.java:185)
    at ActivityReader.main(ActivityReader.java:45)
Caused by: java.net.ConnectException: Connection refused
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
    at java.net.Socket.connect(Socket.java:529)
    at java.net.Socket.connect(Socket.java:478)
    at java.net.Socket.<init>(Socket.java:375)
    at java.net.Socket.<init>(Socket.java:218)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:257)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:298)
    ... 15 more

任何的想法.... ？？？？？？

答案

使用127.0.0.1而不是localhost连接，可能是您系统上发生的事情的线索：

如果你告诉它连接到“localhost”，MySQL将尝试连接到unix套接字。如果您告诉它连接到127.0.0.1，则强制它连接到网络套接字。因此，您可能已将MySQL配置为仅侦听网络套接字而不是文件系统套接字。

https://serverfault.com/questions/295285/mysql-cannot-connect-via-localhost-only-127-0-0-1

另一答案

尝试

>telnet localhost 3306

您应该会看到类似的服务器响应

“5.5.19☺（：* b2p`p☻ǧ4Oph7xxsV5C5mysql_native_password”

最可能的问题将通过用ip替换hostname来修复，检查https://serverfault.com/a/90055

另一答案

我认为您没有在连接URL中指定您的数据库名称 试试这个 conn = DriverManager.getConnection（url +“/”+ dbName，userName，password）; 并确保您已创建具有相同名称的数据库。

另一答案

我在VPS linux服务器上面临同样的问题。我通过用真实IP地址替换localhost或127.0.0.1来解决它。