java - 尝试运行 executeQuery/prepared statements() 时出错

Question

SQL statement is not executedcom.mysql.jdbc.CommunicationsException: Communications link >failure due to underlying exception:

** BEGIN NESTED EXCEPTION **

java.net.ConnectException MESSAGE: Connection refused

STACKTRACE:

java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:310) at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:176) at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:163) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:384) at java.net.Socket.connect(Socket.java:546) at java.net.Socket.connect(Socket.java:495) at java.net.Socket.(Socket.java:392) at java.net.Socket.(Socket.java:235) at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256) at com.mysql.jdbc.MysqlIO.(MysqlIO.java:271) at com.mysql.jdbc.Connection.createNewIO(Connection.java:2771) at com.mysql.jdbc.Connection.(Connection.java:1555) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285) at java.sql.DriverManager.getConnection(DriverManager.java:620) at java.sql.DriverManager.getConnection(DriverManager.java:200) at org.jtdemo.preparedst.main(preparedst.java:18)

** END NESTED EXCEPTION **

Last packet sent to the server was 1 ms ago. at com.mysql.jdbc.Connection.createNewIO(Connection.java:2847) at com.mysql.jdbc.Connection.(Connection.java:1555) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285) at java.sql.DriverManager.getConnection(DriverManager.java:620) at java.sql.DriverManager.getConnection(DriverManager.java:200) at org.jtdemo.preparedst.main(preparedst.java:18)

我的程序是

---

package org.jtdemo;
import java.sql.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class preparedst
{
 //private static final String y = null;

 public static void main(String arg[])throws Exception
 {
 try
 {
  Class.forName("com.mysql.jdbc.Driver");
  String url="jdbc:mysql://localhost:3036/mylib_db";
  Connection con=DriverManager.getConnection(url,"nikki","dkm007");
  String query = " select c.sub_category, b.title,b.author,b.b_key,ta.available_copies" +
    "from Book_dim b,Category_list c,item_availablity_fact ta" +
   " where sub_category = 'Mathematics' and " + 
    " c.category_id=b.category_id and " + 
   " b.b_key=ta.b_key " ;
  /*ps = con.prepareStatement(" select c.sub_category, b.title,b.author,b.b_key,ta.available_copies" +
     "from Book_dim b,Category_list c,item_availablity_fact ta" +
    " where sub_category = ? and " + 
     " c.category_id=b.category_id and " + 
    " b.b_key=ta.b_key ");*///pass sql query ,no parameter passing
  //ps.String(1, "Mathematics"); // set input parameter
  Statement stmt = con.createStatement();
  ResultSet rs = stmt.executeQuery(query) ;
  while(rs.next())
  {

  String scat = rs.getString(1);
  String ttl = rs.getString(2);
  String auth = rs.getString(3);
  int bkey = rs.getInt(4);
  int avcop = rs.getInt(5);
  //String b_key;
  System.out.println("subcategory:"+scat+"title:"+ttl+"author:"+auth+"bookkey:"+bkey+"availcopies:"+avcop);

  }

  con.close();
  //ps.close();
 } 
  catch(Exception e)
        {
         System.out.println("SQL statement is not executed");
         e.printStackTrace();
        }

   }
 }

我正在使用 jdk 1.6，mysql-connector-java-5.0.8-bin.jar，Eclipse 版本:3.5.2。

请帮忙....................

Answer 1

异常告诉你问题所在。如果您的连接被拒绝，那么客户端或服务器的配置有问题。所以首先要检查的是 JDBC URL。您需要验证以下内容:

• 服务器在本地
• 服务器在端口 3036 上提供服务(MySQL 的默认端口是 3306，所以这可能是您的问题)
• 您在该服务器上有一个名为“mylib_db”的数据库
• 您的用户名是正确的
• 您的密码是正确的(以后您可能需要使用占位符文本，例如“密码”)

如果所有这些信息都是正确的，您需要检查您的服务器以确保“nikki”有权通过网络连接到数据库。