Question

我安装了 MYSQLSERVER 5.1 。然后我安装了mysql-connector-java-3.0.8-stable-bin.jar并将驱动器c放入文件夹核心C：\ core.Then在计算机属性中，我创建了变量名为CLASSPATH和变量值的用户变量：C：\ core \ mysql-connector-java-3.0.8-stable-bin.jar。

现在我已经创建了数据库EMPLOYEE4 我的java代码是：

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;

class MySQLTest{


    public static void main(String[] args) {  
        try {  
            Class.forName("com.mysql.jdbc.Driver");  
            Connection dbcon = DriverManager.getConnection(  
                    "jdbc:mysql://localhost:3306/EMPLOYEE", "root", "root");  

        String query ="select count(*) from EMPLOYEE4 ";
             Connection dbCon = null;
        Statement stmt = null;
        ResultSet rs = null;

            //getting PreparedStatment to execute query
            stmt = dbCon.prepareStatement(query);

            //Resultset returned by query
            rs = stmt.executeQuery(query);

            while(rs.next()){
             int count = rs.getInt(1);
             System.out.println("count of stock : " + count);
            }

        } catch (Exception ex) {
             ex.printStackTrace();
            //Logger.getLogger(CollectionTest.class.getName()).log(Level.SEVERE, null, ex);
        } finally{
           //close connection ,stmt and resultset here
        }

    }  
   }

我得到的错误是java.sql.SQLEXCEPTION：通信链接失败：java.IO.Exception底层原因：意外的输入流结束

Answer 1

你应该得到NPE。当您在dbCon而非dbcon

上执行查询时

// initialize here
Connection dbcon = DriverManager.getConnection(  
                "jdbc:mysql://localhost:3306/EMPLOYEE", "root", "root");  

String query ="select count(*) from EMPLOYEE4 ";

// Null here
Connection dbCon = null;

// on dbCon which is null 
stmt = dbCon.prepareStatement(query);

修改

这是你的代码看起来的样子。

Connection dbcon = DriverManager.getConnection( "jdbc:mysql://localhost:3306/EMPLOYEE", "root", "root"); String query = "select count(*) from EMPLOYEE4 "; Statement stmt = dbcon.createStatement(); ResultSet rs = stmt.executeQuery(query);

如何将MySQL与Java连接？

1 个答案: