我是Java的新手，正在尝试使用servlet向数据库中的表添加约会。我能够获取并显示信息，但无法弄清楚如何在表中正确插入新记录。当前，该错误表明名为“ first”的列不存在。但是，当我使用“ query”变量提取信息时，它似乎可以工作。
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class AppointmentServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public AppointmentServlet() {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
// doGet(request, response);
System.out.println("doPost method running");
String first = request.getParameter("firstname");
String last = request.getParameter("lastname");
String day = request.getParameter("day");
String sql = "INSERT INTO \"Reservations\"(\r\n" +
" \"Last\", \"First\", \"Day\")\r\n" +
" VALUES (first, last, day);";
// String query = "SELECT * FROM \"Reservations\"";
Connection c = null;
Statement stmt = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager.getConnection("jdbc:postgresql://localhost:5432/HospitalReservations", "postgres", "coffeeCup");
c.setAutoCommit(false);
System.out.println("Opened database connection successfully.");
System.out.println("C: " + c);
stmt = c.createStatement();
c.commit();
ResultSet rs = stmt.executeQuery(sql);
while ( rs.next() ) {
String firstname = rs.getString("first");
String lastname = rs.getString("last");
String daytime = rs.getString("day");
System.out.println("NAME = " + firstname + " " + lastname);
System.out.println("DAY = " + daytime);
}
} catch( Exception e ) {
System.err.print(e.getClass().getName() + ": " + e.getMessage());
System.exit(0);
}
System.out.println("Operation done successfully.");
response.setContentType("text/html");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>Appointment Response</title>");
out.println("</head>");
out.println("<body>");
out.println("<h3> Reservation Made </h3>");
out.println("<p>" + first + " " + last + " has been added for " + day + "</p>");
out.println("</body>");
out.println("</html>");
}
}
需要传递参数时使用PreparedStatement。例如，在您的情况下：
//use ? for parameter placeholder
String sql = "INSERT INTO \"Reservations\"(\r\n" +
" \"Last\", \"First\", \"Day\")\r\n" +
" VALUES (?, ?, ?);";
PreparedStatement preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, last);
preparedStatement.setString(2, first);
preparedStatement.setString(3, day);
preparedStatement.execute();
注： preparedStatement.setXXX方法的第一个参数称为parameterIndex，它以1开头，第一个参数为1，第二个参数为2，...