如何在servlet -jsp / jsp-servlet中过滤arraylist结果？

Question

在我的项目中，你好朋友，我有一个arraylist在给定数据库内容的jsp页表中显示结果，我想向其中添加一个过滤器以仅显示list中匹配的内容，

the table which is coming out is as:
student_id class_id student_name
1x0001        10         Ashish
1x2001        11         Alex
1x2002        11         Atr.
1x0001        10         Alok

.............going on...

但我希望结果仅显示class_id :: 11的页面，并删除其他结果该怎么做？

List dataList = new ArrayList();
rs = s.getResultSet();
      while (rs.next ()){
        //Add records into data list
        dataList.add(rs.getInt("class_id"));
        dataList.add(rs.getString("name"));
        dataList.add(rs.getString("student_id"));
      }

然后通过获取arraylist在servlet中显示结果：我想要的是将问题显示为具有arraylist而不是DB的过滤表：

the table which is coming(result???) out on servlet is as:
    student_id class_id student_name
    1x2001        11         Alex
    1x2002        11         Atr.

    .............going on...

Answer 1

问题出在哪儿。 把这个条件放在像这样的SQL查询中， where class_id = ? 。

Answer 2

您应该像Adeel所说的那样在SQL层进行过滤。

同样，您应该使用Bean / Class / Struct来保存每个记录，而不是将所有非结构化数据堆积到单个ArrayList中。

不过，以下代码可以满足您的要求：

public class FilterTest {
    public static int COLS_PER_RECORD = 3;

    public static void main(String[] args) {
        ArrayList dataList = populateTestData();
        printRecords(dataList);
        ArrayList filtered = filterForClassId(dataList, 2);
        printRecords(filtered);
    }

    private static ArrayList populateTestData() {
        ArrayList dataList = new ArrayList();
        ResultSet rs = s.getResultSet();
        while (rs.next()) {
            dataList.add(rs.getInt("class_id"));
            dataList.add(rs.getString("name"));
            dataList.add(rs.getString("student_id"));
        }
        return dataList;
    }

    private static ArrayList filterForClassId(ArrayList dataList,
            int classIdToFilterFor) {
        ArrayList filtered = new ArrayList();
        Integer classIdToFilterForInteger = new Integer(classIdToFilterFor);
        for (int i = 0; i < dataList.size(); i += COLS_PER_RECORD) {
            if (classIdToFilterForInteger.equals(dataList.get(i))) {
                for (int j = 0; j < COLS_PER_RECORD; j++) {
                    filtered.add(dataList.get(i + j));
                }
            }
        }
        return filtered;
    }

    private static void printRecords(ArrayList dataList) {
        System.out.println("----");
        for (int i = 0; i < dataList.size(); i += COLS_PER_RECORD) {
            System.out.println("class_id=" + dataList.get(i) + " name="
                    + dataList.get(i + 1) + " student_id="
                    + dataList.get(i + 2));
        }
        System.out.println("----");
    }
}