简单的数据库操作类

import java.sql.Connection;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.DriverManager;
import java.sql.*;

/**
 * 多复用的数据库操作类
 */
public class CntDataBase {
    private Connection conn = null;
    private Statement stmt = null;
    ResultSet rs = null;

    public CntDataBase() {}

    public void openConn() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost/mytest",
                                               "username", "password");
        } catch (Exception e) {
            System.out.println("加载驱动器类时出现异常");
            e.printStackTrace();
        }
    }

    public void executeUpdate(String sql) {
        stmt = null;
        rs = null;
        try {
            stmt = conn.createStatement();
            stmt.executeUpdate(sql);
        } catch (SQLException ex) {
            System.out.println("executeUpdate时出现异常");
            ex.printStackTrace();
        }

    }

    public Statement getStmt(String sql) {
        stmt = null;
        rs = null;
        try {
            stmt = conn.createStatement();
            stmt.executeUpdate(sql);
        } catch (SQLException ex) {
            System.out.println("getStmt时出现异常");
            ex.printStackTrace();
        }
        return stmt;

    }

    public ResultSet getRs(String sql) {
        stmt = null;
        rs = null;
        try {
            stmt = conn.createStatement();
            rs = stmt.executeQuery(sql);
        } catch (SQLException ex) {
            System.out.println("getRs时出现异常");
            ex.printStackTrace();
        }
        return rs;
    }

    public void closeDataBase() {
        try {
            if (rs == null) {
                stmt.close();
                conn.close();
            } else if (stmt == null) {
                rs.close();
                conn.close();
            } else if (rs == null && stmt == null) {
                conn.close();
            } else {
                rs.close();
                stmt.close();
                conn.close();
            }
        } catch (SQLException e) {
            System.out.println("关闭数据库连接时出现异常");
            e.printStackTrace();
        }
    }
}