1，request.getParamter()是返回String类型，而request.setAtrribute()是返回Object类型的，想要将Object类型 a 转换为String类型 String b = a.toString().
2，为了防止报空指针 所以接收的数据进行判断的时候都要放在equals()内。比如message!=null&&!"".equals(message).
3，表单传输时一定要有method方法不然根本没有办法传输出去。
4，使用
方法传递数据到servlet中，servlet返回到界面时，一定要注意路径，路径必须是从目录出发的。
5，统计数据库表中的数据条数 select count(*)as totalCount from demand_form 具体JavaBean代码如下：
/**
* 统计数据库中数据的总数
*/
public int total() {
int total = 0;
Connection con = connect.getCon();
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
pstmt = con.prepareStatement("select count(*)as totalCount from demand_form");
rs = pstmt.executeQuery();
if(rs.next()) {
total = rs.getInt("totalCount");
}
} catch (SQLException e) {
// TODO 自动生成的 catch 块
connect.close(rs,pstmt, con);
}
return total;
}
按时间段查找数据 以及数据条数 select*from demand_form where date between '2019-03-05' and '2019-03-06' limit 0,5;
select count(*)as totalCount from demand_form where date between '2019-03-05' and '2019-03-06';
具体Javabean代码
/**
* 按时间段查找需求表单
*/
public ArrayList<demand> queryTimedemand(String date1,String date2,int a){
Connection con = connect.getCon();
ArrayList<demand> list = new ArrayList<>();
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
pstmt = con.prepareStatement("SELECT*FROM demand_form where date BETWEEN '"+date1+"' and '"+date2+"' limit "+a*5+","+(a+1)*5);
rs = pstmt.executeQuery();
while (rs.next()) {
demand dem = new demand();
dem.Set(rs.getString(1), rs.getString(2), rs.getString(3).split("&"), rs.getString(4), rs.getDouble(5), rs.getString(6),rs.getString(7),rs.getString(8));
dem.setPass(rs.getString(9));
list.add(dem);
}
return list;
} catch (SQLException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
return null;
} finally {
connect.close(rs,pstmt, con);
}
}
/**
* 按时间段统计表单数据条
*/
public int Timetotal(String date1,String date2) {
int total = 0;
Connection con = connect.getCon();
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
pstmt = con.prepareStatement("select count(*)as totalCount from demand_form where date BETWEEN '"+date1+"' and '"+date2+"'");
rs = pstmt.executeQuery();
if(rs.next()) {
total = rs.getInt("totalCount");
}
} catch (SQLException e) {
// TODO 自动生成的 catch 块
connect.close(rs,pstmt, con);
}
return total;
}