java如何在JSONArray中存储唯一的元素

Question

我试图将从数据库中获取的唯一元素存储在JSONArray中

HashSet<String> hs = new HashSet<String>();
JSONArray mainarray=new JSONArray();

PreparedStatement stmt = connection.prepareStatement("SELECT * from categories");
ResultSet rs=stmt.executeQuery();

while(rs.next())
{
    String T1 = rs.getString("T1");
    hs.add(T1);
    if(!hs.contains(T1))
    {
        mainarray.put(T1);
    }
}


System.out.println(mainarray); 

首先，输出是一个空数组[]

顺便说一下，我正在使用org.json.JSONArray

谁能帮忙吗

Answer 1

调整查询，就不需要处理Java代码中的重复项

JSONArray mainarray=new JSONArray();

PreparedStatement stmt = connection.prepareStatement("SELECT DISTINCT T1 from categories");
ResultSet rs=stmt.executeQuery();

while(rs.next()) {
    String T1 = rs.getString("T1");
    mainarray.put(T1);
}
System.out.println(mainarray);