java - 使用java jdbc在vista上连接mysql，通讯异常，尝试了常见的答案

Question

我在 Vista 64 位平台上使用 java 获取 mysql 连接时遇到新手问题。我一直在阅读其他有类似问题的网络信息，到目前为止还没有运气。这可能是由于我缺乏理解。我可以使用 netstat -an 看到端口 3306 正在监听。我禁用了 MS 防火墙并安装了 webroot，因为我的防火墙和 mysql 是允许的。我已在 -cp 选项中添加了 JDBC 驱动程序 jar 文件的路径。调试似乎表明驱动程序未注册，但我可以从命令行对数据库执行所有mysql功能。

我看到了以下异常: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException:通信链路故障

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

这是我的输出:

C:\Users\Jerry>java -cp c:\Users\jerry;c:\ProgramFiles(86)\ConnectorJ\mysql-connector-java-5.1.11-bin dbaccess 
FOO:  jdbc:mysql://127.0.0.1:3306/access03tstroot
Cannot connect to database server
SQLEXCEPTION: com.mysql.jdbc.Driver
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at dbaccess.mysqlConnection(dbaccess.java:77)
at dbaccess.main(dbaccess.java:59)

我打印出我要发送的消息，并设置断点以在 DriverManager.getConnection 中停止。我认为有一段代码可以检查已注册的驱动程序。

代码在 isDriverAllowed(aDriver.driver, callCL) 期间失败 据我了解，Class.forName 调用将在找到时注册一个新的驱动程序。 该循环进行两次传递，首先查找 ODBC 驱动程序，然后查找 com.mysql.jdbc.driver。

调用者CL = sun.misc.Launcher$AppClassLoader@1054f93 url 是 jdbc:mysql:/loacalhost:3306/access03tst

    for(DriverInfo aDriver : registeredDrivers) {
        // If the caller does not have permission to load the driver then
        // skip it.
        if(isDriverAllowed(aDriver.driver, callerCL)) {
            try {
                println("    trying " + aDriver.driver.getClass().getName());
                Connection con = aDriver.driver.connect(url, info);
                if (con != null) {
                    // Success!
                    println("getConnection returning " + aDriver.driver.getClass().getName());
                    return (con);
                }
            } catch (SQLException ex) {
                if (reason == null) {
                    reason = ex;
                }
            }

        } else {
            println("    skipping: " + aDriver.getClass().getName());
        }

    }

我的编译命令是:

javac -d . -sourcepath . -cp c:\Users\Jerry;c:\ProgramFiles(86)\ConnectorJ\mysql-connector-java-5.1.11-bin c:\Users\Jerry\dbaccess.java

我的执行命令是:

java -cp c:\Users\jerry;c:\ProgramFiles(86)\ConnectorJ\mysql-connector-java-5.1.11-bin dbaccess

我的代码如下:

package dbaccess;

import java.sql.*;
import java.lang.*;

public class dbaccess
{
    // Public static indicates that this is a class variable not an instance
    // variable. It is part of the class as a whole.
    public static Connection conn = null;
    public boolean success;

    public static void main (String[] args)
    {
        init();
        mysqlConnection();
        getList catList = new getList();
        boolean status = catList.success;
    }
    public static void mysqlConnection()
    {
       try
       {
          String dbName  =  "access03tst";
          String userName = "";
          String password = "";
          String url = "jdbc:mysql://localhost:3306/";
          String driver = "com.mysql.jdbc.driver";
          String foo = url+dbName+userName+password;
          System.out.println("FOO: " + foo);

          //Register the JDBC driver for MySQL.
          Class.forName("com.mysql.jdbc.Driver"); //.newInstance ();

          System.out.println("Surprise we got here ");
          conn = DriverManager.getConnection(url+dbName+userName+password);
          System.out.println ("Database connection established");
          System.out.println("URL: " + url);
          System.out.println("Connection: " + conn);
       }
       catch (Exception e)
       {
           System.err.println ("Cannot connect to database server");
       }
       finally
       {
          if (conn != null)
          {
              try
              {
                 conn.close ();
                 System.out.println ("Database connection terminated");
              }
              catch (Exception e) { /* ignore close errors */ }
          }
       }  // end finally
    }

    public static void init()
    {
    //
    // Public static indicates that this is a class variable not an instance
    // variable. It is part of the class as a whole.
    conn = null;
    boolean success = false;
    boolean CatRequest = false;
    }

}

Answer 1

我终于找到答案了。我使用了许多引用文献中的 url 语法。

      String userName = "root";
      String password = "password";
      String url = "jdbc:mysql://localhost:3306/";
      conn = DriverManager.getConnection(url+dbName+userName+password);

这会导致 url 传递到 getConnection 代码中，显示为 “jdbc:mysql://localhost:3306/dbaccess03tstroot密码” MySQL 查找名为 dbaccess03tstrootpassword 的数据库，该数据库不存在并导致失败的连接为 null。

我将代码更改为以下语法，并获得了有效的连接。

String urlFormated = "jdbc:mysql://localhost:3306/"
              + dbName 
              + "?user="
              + userName
              + "&password="
              + password;
conn = DriverManager.getConnection(urlFormated);