java - 如何将java中HashMap中表的多个值发送到jsp？

Question

我想从 java tp 中的 hashmap 发送一个 jsp 文件中数据库表中的多个值。这就是我到目前为止所做的

    ResultSet rs = st.executeQuery("SELECT * FROM seeding where scheme = '"+user+"' "); 
    HashMap<String, String> verify = new HashMap<String, String>();
    while (rs.next())
    {
    verify.put("beneficiaryID",rs.getString("beneficiaryID"));
    verify.put("scheme", rs.getString("scheme"));
    verify.put("aadhaar",rs.getString("aadhaar"));
    verify.put("name",rs.getString("name"));
    }
    request.setAttribute("verify", verify);

jsp>>

<%
HashMap<String, String> verify = (HashMap<String, String>) 
request.getAttribute("verify");
for (String key : verify.keySet())  
{ 
out.print(verify.get("aadhaar"));
out.print(verify.get("scheme"));
out.print(verify.get("beneficiaryID")+"$"+verify.get("name"));
}

但这只给出了表的最后一行，而不是所有结果! 需要改变什么？ 谢谢

Answer 1

考虑这段代码:

HashMap<String, String> verify = new HashMap<String, String>();
while (rs.next())
{
    verify.put("beneficiaryID",rs.getString("beneficiaryID"));
    verify.put("scheme", rs.getString("scheme"));
    verify.put("aadhaar",rs.getString("aadhaar"));
    verify.put("name",rs.getString("name"));
}

每次循环(针对数据库中的每一行或每个结果集行)，您都会将相同的条目放入 Map 中并使用新值。

每一行都会覆盖前一行。

您无法在 JSP 中取出它们，因为您覆盖了除最后一个之外的所有内容。

有几种解决方案。我将创建一个具有 4 个属性的 POJO 类，并将每行结果放入一个列表中。但是，让我们使用您的 map 创意:

List results = new ArrayList<Map<String, String>>();
while (rs.next())
{
    Map<String, String> verify = new HashMap<String, String>();
    verify.put("beneficiaryID",rs.getString("beneficiaryID"));
    verify.put("scheme", rs.getString("scheme"));
    verify.put("aadhaar",rs.getString("aadhaar"));
    verify.put("name",rs.getString("name"));
    results.add(verify);
}
 request.setAttribute("verify", results);

现在您必须稍微更改一下 JSP(其中包含丑陋的 java 代码):

<%
List<Map<String, String>> results = (List<Map<String, String>>)request.getAttribute("verify");
for (Map<String, String> verify: results) {
{ 
    out.print(verify.get("aadhaar"));
    out.print(verify.get("scheme"));
    out.print(verify.get("beneficiaryID")+"$"+verify.get("name"));
}
%>