数据库连接类

package system.dao;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.PreparedStatement;
import java.sql.Statement;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Vector;
import java.sql.ResultSetMetaData;

public class DBCon {
  public DBCon() {
  }

  //属性设置
  private PreparedStatement pstmt;
  private Statement st;
  private Connection conn;
  private ResultSet rs;
  //获取数据库连接
  private Connection getConnection() {
    try {
      //注册驱动器
      Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
      //创建连接
      conn = DriverManager.getConnection(
          "jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=pubs;",
          "sa", "");
    }

    catch (ClassNotFoundException ex) {
      ex.printStackTrace();
    }
    catch (SQLException ex) {
      /** @todo Handle this exception */
      ex.printStackTrace();
    }

    return conn;
  }

  //插入、修改、删除
  public boolean preChange(String sql, Object[] data) {
    boolean flag = false;
    //获取连接
    conn = this.getConnection();
    try {
      pstmt = conn.prepareStatement(sql);
      for (int i = 1; i <= data.length; i++) {
        pstmt.setObject(i, data[i - 1]);
      }
      int count = pstmt.executeUpdate();
      if (count > 0) {
        flag = true;
      }
      else {
        flag = false;
      }
    }
    catch (SQLException ex) {