SQLException ResultSet

每个方法里都有关闭数据库连接，导致rs=db.executeQuery(sql)之后rs.next()出错。

package com.db;
import java.io.*;
import java.sql.*;

public class sqlBean {
	public Connection conn = null;
	public ResultSet rs = null;
	
	private String DatebaseDriver = "com.mysql.jdbc.Driver";
	private String DatebaseConnStr = null;
	
	public void setDatebaseDriver(String Driver){
		this.DatebaseDriver = Driver;
	}
	
	public String getDatebaseDriver(){
		return (this.DatebaseDriver);
	}
	
	public void setDatebaseConnStr(String ConnStr){
		this.DatebaseConnStr = ConnStr;
	}
	
	public String getDatebaseConnStr(){
		return (this.DatebaseConnStr);
	}
	
	public sqlBean(){
		try{
			Class.forName(DatebaseDriver);
		}
		catch(ClassNotFoundException e){
			System.err.println("加载驱动器失败" + e.getMessage());
			System.out.print("执行插入有错误" + e.getMessage());
		}
	}
	
	public int executeInsert(String sql){
		int num = 0;
		try{
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/charge?useUnicode=true&characterEncoding=GBK", "root", "mysql51");
			Statement stmt = conn.createStatement();
			num = stmt.executeUpdate(sql);
		}
		catch(SQLException ex){
			System.err.println("执行插入有错误" + ex.getMessage());
			System.out.print("执行插入有错误" + ex.getMessage());
		}
		CloseDateBase();
		return num;
	}
	
	public ResultSet executeQuery(String sql){
		rs = null;
		try{
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/charge?useUnicode=true&characterEncoding=GBK", "root", "mysql51");
			Statement stmt = conn.createStatement();
			rs = stmt.executeQuery(sql);
		}
		catch(SQLException ex){
			System.err.println("执行查询有错误" + ex.getMessage());
			System.out.print("执行查询有错误" + ex.getMessage());
		}
		//CloseDateBase();
		return rs;
	}
	
	public int executeDelete(String sql){
		int num = 0;
		try{
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/charge?useUnicode=true&characterEncoding=GBK", "root", "mysql51");
			Statement stmt = conn.createStatement();
			num = stmt.executeUpdate(sql);
		}
		catch(SQLException ex){
			System.err.println("执行删除有错误" + ex.getMessage());
			System.out.print("执行删除有错误" + ex.getMessage());
		}
		CloseDateBase();
		return num;
	}
	
	public void CloseDateBase(){
		try{
			conn.close();
		}
		catch(Exception end){
			System.err.println("关闭conn时出错" + end.getMessage());
			System.out.print("关闭conn时出错" + end.getMessage());
		}
	}

}