如何将MySQL与Java连接？

Question

I have installed MYSQLSERVER 5.1 .Then I installed mysql-connector-java-3.0.8-stable-bin.jar and put in drive c with folder core that is C:\\core.Then in properties of computer I create user variable with variable name CLASSPATH and variable value:C:\\core\\mysql-connector-java-3.0.8-stable-bin.jar.

Now I have created database EMPLOYEE4 My java code is:

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
        }

    }  
   }

I get error that java.sql.SQLEXCEPTION:communication link failure:java.IO.Exception underlying cause:Unexpected end of input stream

Answer 1

You should be getting NPE. As you are executing your query on dbCon and not on dbcon

// 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);

EDIT

This how your code suppose to look like.

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);