java - 将数据导出到双数组

我想将从数据库检索到的数据添加到数组中，但其检索数据为空。我的错是什么？请帮帮我。

for (User u : userLists) {
            for (Resource r : resourceLists) {

                String ratingQuery
                        = "SELECT rank FROM ratings WHERE userindex='"
                        + u.getIndex()
                        + "' AND resourceindex='"
                        + r.getIndex()
                        + "'";

                try {
                    ratingCon = ConnectionManager.getConnection();
                    stmt = ratingCon.prepareStatement(ratingQuery);
                    rs = stmt.executeQuery();

                    while (rs.next()) {
                    rate = rs.getDouble("rank");
                    ratings[u.getIndex()][r.getIndex()] = rate; //it seems here is the problem
                    }

                } catch (Exception e) {
                    System.out.println("Log In failed: An Exception has occurred! " + e);
                }
            }
        }

最佳答案

如果ratings是一个二维双精度数组，则这一行没有问题：

ratings[u.getIndex()][r.getIndex()] = rate;

但可能是您的数据库返回空的ResultSet？插入要调试的打印语句：

  while (rs.next()) {
      rate = rs.getDouble("rank");
       System.out.println("Result set is not empty! Current rank is: " + rate);
      ratings[u.getIndex()][r.getIndex()] = rate; //it seems here is the problem
  }

如果它什么也不打印-那么问题不在代码中而是在数据库数据中。另外，我认为您在查询结束时遗漏了分号;。
关于异常处理：

 catch (Exception e) {
     System.out.println("Log In failed: An Exception has occurred! " + e);
 }

您在这里捕获的异常类型太抽象-您不知道它是SQLException异常还是ArrayIndexOutOfBoundsException。换成几个挡块。