java - 带有 MYSQL 的 JSP 中的 NoSuchElementException

Question

我不断收到以下异常:org.apache.jasper.JasperException: java.util.NoSuchElementException

你能帮我处理我的代码吗，因为我显然遗漏了一些东西。非常感谢!

JSP 文件:

    <%
  Enumeration names = request.getParameterNames();
  while (names.hasMoreElements()) {
  String name = (String) names.nextElement();
  StringBuffer sb = new StringBuffer(name);
  sb.deleteCharAt(0);
  VoCo.Vogel.Delete(sb.toString());
}

%>
<br>

<div class="navigator">
<a href="index.jsp">Add</a>
<a id="currenttab" href="waarnemingen.jsp">Delete</a>
</div>

<br> <br> <br>

<form action="waarnemingen.jsp" method="post">
<table>
<tr>
<th>Datum</th>
<th>Tijd</th>
<th>Plaats</th>
<th>Spotternaam</th>
<th>Vogelsoort</th>
</tr> 
<%

List list = VoCo.Vogel.GetWaarnemingen();
int id = 0;
String box = null;

Iterator<String> it = list.iterator();

while (it.hasNext()) {
  id = Integer.parseInt(it.next());
  out.print("<tr>");
  for (int i = 0; i < 5; i++) {
      out.print("<td>");
      out.print(it.next());
      out.print("</td>");
}
out.print("<td>");
box = "<input name=r" + id + " type='checkbox'>";
out.print(box);
out.print("</td>");
out.print("</tr>");
}
%>

</table>

<br>
<input type="submit" value="Delete">

</form>

java文件:

    public class Vogel {
static final String url = "jdbc:mysql://localhost:3306/turving";

public static void Insert(String datum, String tijd, String plaats, String spotternaam, String vogelsoort) {
  try {

      String insert = "INSERT INTO turving(datum, tijd, plaats, spotternaam, vogelsoort)" + "VALUES (?, ?, ?, ?, ?)";

      Class.forName("com.mysql.jdbc.Driver");
      Connection con = DriverManager.getConnection(url, "root", "");

      PreparedStatement ps = con.prepareStatement(insert);

      ps.setString(1, datum);
      ps.setString(2, tijd);
      ps.setString(3, plaats);
      ps.setString(4, spotternaam);
      ps.setString(5, vogelsoort);
      ps.executeUpdate();
      con.close();

  } catch (Exception ex) {
      Logger.getLogger(Vogel.class.getName()).log(Level.SEVERE, null, ex);
  }
 }

 public static List GetWaarnemingen() {

  List<String> list = new ArrayList<String>();

  try {

      Class.forName("com.mysql.jdbc.Driver");
      Connection con = DriverManager.getConnection(url, "root", "");

      Statement stmt = con.createStatement();

      ResultSet result = stmt.executeQuery("SELECT * FROM turving");

      while(result.next())
      {
         list.add(result.getString("id"));
         list.add(result.getString("datum"));
         list.add(result.getString("tijd"));
         list.add(result.getString("plaats"));
         list.add(result.getString("spotternaam"));
         list.add(result.getString("vogelsoort"));
      } 

      con.close();

  } catch (Exception ex) {
      Logger.getLogger(Vogel.class.getName()).log(Level.SEVERE, null, ex);
  }
      return list;
  }

 public static void Delete(String id) {
  try {
      String delete = "DELETE from turving WHERE id = ?";

      Class.forName("com.mysql.jdbc.Driver");
      Connection con = DriverManager.getConnection(url, "root", "");
      PreparedStatement ps = con.prepareStatement(delete);

      ps.setString(1, id);
      ps.executeUpdate();
      con.close();

  } catch (Exception ex) {
      Logger.getLogger(Vogel.class.getName()).log(Level.SEVERE, null, ex);
  }
 }
}

Answer 1

问题出在这里:

 Iterator<String> it = list.iterator();

 while (it.hasNext()) {
   id = Integer.parseInt(it.next());
   out.print("<tr>");
   for (int i = 0; i < 5; i++) {
       out.print("<td>");
       out.print(it.next());
       out.print("</td>");
 }

您调用 it.next() 的次数过多。第一次调用应保存在一个变量中，这样您就不会在子循环中再次调用它。

应该是这样的:

 Iterator<String> it = list.iterator();

 while (it.hasNext()) {
   String item = (String)it.next();
   id = Integer.parseInt(item);
   out.print("<tr>");
   for (int i = 0; i < 5; i++) {
       out.print("<td>");
       out.print(item);
       out.print("</td>");
 }