如何比較兩個在jsp中選擇的arraylist和set選項？

Question

我有兩個表：

表1帶列的geoCountry

country_name | country_code

表2帶有列的user_countries

country_name | username 

我想設置用戶國家預選（即從數據庫中獲取）

這是我嘗試過的代碼

     <select multiple="multiple" class="country" style="width: 200px">
         <%
           sql6 = "SELECT DISTINCT countryname FROM user_countries WHERE username = ?";
           ps6 = connection.prepareStatement(sql6);
           ps6.setString(1, user);
           rs6 = ps6.executeQuery();

            while (rs6.next()) {
                usercountries.add(rs6.getString(1));
             }

            for (int i = 0; i < geoCountry.size(); i++) {
                 for (int j = 0; j < usercountries.size(); j++) {
                    if (usercountries.get(j).equals(geoCountry.get(i))) {
                 %>
                <option value="<%=geoCountry.get(i)%>" selected="selected"><%=geoCountry.get(i)%></option>
                 <% } else {%>
                 <option value="<%=geoCountry.get(i)%>"><%=geoCountry.get(i)%></option>
              <% }
              }
           } %>
      </select>

它在選擇框中顯示重復的值..為什么？

Answer 1

用“ usercountries” thms刪除第二個循環。 喜歡：

  for (int i = 0; i < geoCountry.size(); i++) {
         if (usercountries.contains(geoCountry.get(i)) {
             %>
            <option value="<%=geoCountry.get(i)%>" selected="selected"><%=geoCountry.get(i)%></option>
             <% } else {%>
             <option value="<%=geoCountry.get(i)%>"><%=geoCountry.get(i)%></option>
          <% }
       } %>