今日学习笔记

翻页函数的实现

int pl = 10, pn = 1, cn = 0, tn =  userService.queryUserCount();

int tp = (tn / pl + tn % pl == 0 ? 0 : 1);
if (pageNum != null) {
    pn = Integer.parseInt(pageNum);
}
if (changeNum != null) {
    cn = Integer.parseInt(changeNum);
}

if (!(pn == 1 && cn == -1) && !(pn == tp && cn == 1)){
    pn = pn + cn;
}
//pl是pageline表示每页显示多少条;pn是pagenum;cn是上一页、下一页、查询等changenum;tn是totalnum总条数；tp是总页数


建立传参

StringBuffer sql = new StringBuffer("select count(*) as usercount from userInfo u ");
    sql.append(" where 1 = 1");
    if (u.getUserId() != null && !"".equals(u.getUserId())) {
        sql.append(" and u.userId like '%" + u.getUserId() + "%' ");
    }
    if (u.getUserName() != null && !"".equals(u.getUserName())) {
        sql.append(" and u.userName like '%" + u.getUserName() + "%' ");
    }
    MySqlDB mySqlDB = new MySqlDB();
    Connection conn = mySqlDB.getConn();
    Statement stmt = null;
    ResultSet rs = null;
    int userCount = 0;
    try {
        stmt = conn.createStatement();
        rs = stmt.executeQuery(sql);
        while (rs.next()) {
            userCount = rs.getInt("userCount");
        }
    } catch (SQLException throwables) {
        throwables.printStackTrace();

    } finally {
        assert rs != null;
        rs.close();
        stmt.close();
        conn.close();//先进后出，后进先出
    }
    return userCount;
}

@Override
public User queryUserById(String userId) throws SQLException {
    String sql = "select u.* from userInfo u where u.userId='"+userId+"'";
    User user = null;
    MySqlDB mySqlDB = new MySqlDB();
    Connection conn = mySqlDB.getConn();
    Statement stmt = null;
    ResultSet rs = null;
    try {
        stmt = conn.createStatement();
        rs = stmt.executeQuery(sql);
        while (rs.next()) {
             user = new User();
            user.setUserId(rs.getString("userId"));
            user.setUserName(rs.getString("userName"));
            user.setUserPassword(rs.getString("userPassword"));
            user.setRoleId(rs.getInt("roleId"));
        }
    } catch (SQLException throwables) {
        throwables.printStackTrace();