全面了解JAVA_BaseDAO数据处理类

package dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;


public class BaseDao {
  private String drive="com.microsoft.sqlserver.jdbc.SQLServerDriver";
  private String url="jdbc:sqlserver://localhost:1433;DatabaseName=BookManage";
  private String user="sa";
  private String password="";
  protected Connection conn;
  protected PreparedStatement ps;
  protected ResultSet rs;
  public Connection getCon(){
    try {
      Class.forName(drive);
      cOnn=DriverManager.getConnection(url, user, password);
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    } catch (SQLException e) {
      e.printStackTrace();
    }
    
    return conn;
  }
  public void allClos(ResultSet rs,PreparedStatement ps,Connection conn){
  
      try {
        if(rs!=null){
        rs.close();
        }
        if(ps!=null){
          ps.close();
          }
        if(conn!=null){
          conn.close();
          }
      } catch (SQLException e) {
        e.printStackTrace();
      }
    }
public int executeUpdate(String sql,Object...str){
  int num=0;
  try {
    ps=getCon().prepareStatement(sql);
    if(ps!=null){
      for(int i=0;i