下面的HTML页面和Java Servlet负责将员工详细信息更新到数据库中。根据HTML页面，要更新的字段是可选的，但是，空字段也将作为空字符串更新到数据库中。
例如，如果我只想更改员工的小时工资率，我会将其他所有内容留空，因此这些空白值也会作为空字符串更新到数据库中，而不是保留在以前的值
支持可选更新字段的正确方法是什么？
<div id="container">
<h1>Update Employee Details</h1>
<h3>(All update fields are optional)</h3>
<form action ="UpdateEmployeeAccount" method = "post">
<table border ="1">
<tr>
<td>Employee ID (of employee to be updated)</td>
<td><input type = "text" name = "update_id" pattern="[0-9]{4}" title="4 digit number: e.g. 1234" maxlength="4" required></td>
</tr>
<tr>
<td>New Admin Status</td>
<td>
<input type = "radio" name = "NewAdminStatus" value ="1">Yes
<input type = "radio" name = "NewAdminStatus" value = "0" >No
</td>
</tr>
<tr>
<td>New Residential Address</td>
<td><input type = "text" name = "newAddress">
</tr>
<tr>
<td>Revised Hourly Pay Rate ($)</td>
<td><input type = "number" name = "NewPay" min="0" step="0.01">
</tr>
<tr>
<td>New Role:</td>
<td><input type = "text" name = "NewRole" >
</tr>
<tr>
<td>New BSB Number</td>
<td><input type = "text" name = "NewBSB" pattern="[0-9]{6}" title="6-digit BSB number e.g. 123456" maxlength="6" >
</tr>
<tr>
<td>New Bank (if employee has changed bank)</td>
<td><input type = "text" name = "NewBank">
</tr>
<tr>
<td>New Bank Account Number</td>
<td><input type = "text" name = "NewBAN" pattern="[0-9]{12}" title="Please enter a valid Bank Account Number" maxlength="12">
</tr>
<tr>
<td>New Superannuation Company</td>
<td><input type = "text" name = "NewSAC">
</tr>
<tr>
<td>New Superannuation Number</td>
<td><input type = "text" name = "NewSAN">
</tr>
</table>
<br>
<br>
<input type = "submit" value = "Update Employee Details">
</form>.
</div>
</body>
</html>
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
public class UpdateEmployeeAccount extends HttpServlet {
protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String update_id = request.getParameter("update_id");
String NewAdminStatus = request.getParameter("NewAdminStatus");
String newAddress = request.getParameter("newAddress");
String NewPay = request.getParameter("NewPay");
String NewRole = request.getParameter("NewRole");
String NewBSB = request.getParameter("NewBSB");
String NewBank = request.getParameter("NewBank");
String NewBAN = request.getParameter("NewBAN");
String NewSAC = request.getParameter("NewSAC");
String NewSAN = request.getParameter("NewSAN");
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/payroll_system", "root", "");
PreparedStatement ps = con.prepareStatement("UPDATE payroll_system.employee_info SET Admin=?, Address=?, HourlyRate=?, Role=?, BSB=?, BankName=?, Accnumber=?, SuperNumber=?, SuperCompany=? WHERE employeeID=?");
ps.setString(1, NewAdminStatus);
ps.setString(2, newAddress);
ps.setString(3, NewPay);
ps.setString(4, NewRole);
ps.setString(5, NewBSB);
ps.setString(6, NewBank);
ps.setString(7, NewBAN);
ps.setString(8, NewSAN);
ps.setString(9, NewSAC);
ps.setString(10, update_id);
int i = ps.executeUpdate();
if(i>0) {
PreparedStatement pd = con.prepareStatement("UPDATE payroll_system.employee_login SET Admin=? WHERE employeeID=?");
pd.setString(1, NewAdminStatus);
pd.setString(2, update_id);
pd.executeUpdate();
out.println("Employee Details Successfully Updated");
RequestDispatcher rs = request.getRequestDispatcher("UpdateEmployee.html");
rs.include(request, response);
}
}catch(Exception e)
{
e.printStackTrace();
out.println("Failed to update details");
RequestDispatcher rs = request.getRequestDispatcher("UpdateEmployee.html");
rs.include(request, response);
}
out.close();
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
}
答案 0 :(得分：1)
您可以在Java中将空参数设置为NULL：
if(NewAdminStatus.isEmpty()) ps.setNull(1, Types.VARCHAR) else ps.setString(1, NewAdminStatus);
if(newAddress.isEmpty() ) ps.setNull(2, Types.VARCHAR) else ps.setString(2, newAddress );
if(NewPay.isEmpty() ) ps.setNull(3, Types.VARCHAR) else ps.setString(3, NewPay );
if(NewRole.isEmpty() ) ps.setNull(4, Types.VARCHAR) else ps.setString(4, NewRole );
if(NewBSB.isEmpty() ) ps.setNull(5, Types.VARCHAR) else ps.setString(5, NewBSB );
if(NewBank.isEmpty() ) ps.setNull(6, Types.VARCHAR) else ps.setString(6, NewBank );
if(NewBAN.isEmpty() ) ps.setNull(7, Types.VARCHAR) else ps.setString(7, NewBAN );
if(NewSAN.isEmpty() ) ps.setNull(8, Types.VARCHAR) else ps.setString(8, NewSAN );
if(NewSAC.isEmpty() ) ps.setNull(9, Types.VARCHAR) else ps.setString(9, NewSAC );
...并在NULL中处理SQL，就像那样：
UPDATE payroll_system.employee_info
SET Admin = COALESCE(?, Admin ),
Address = COALESCE(?, Address ),
HourlyRate = COALESCE(?, HourlyRate ),
Role = COALESCE(?, Role ),
BSB = COALESCE(?, BSB ),
BankName = COALESCE(?, BankName ),
Accnumber = COALESCE(?, Accnumber ),
SuperNumber = COALESCE(?, SuperNumber ),
SuperCompany = COALESCE(?, SuperCompany)
WHERE employeeID = ?