迭代ResultSet并在ArrayList中添加其值 [英] Iterating over ResultSet and adding its value in an ArrayList

问题描述

我正在迭代 ResultSet 并尝试在 ArrayList 中复制其值。
问题是它的遍历只有一次。但是使用 resultset.getString（Col 1）到 resultset.getString（'Col n）显示全部所有列的条目。
下面是代码片段 -

I am iterating over an ResultSet and trying to copy its values in an ArrayList. The problem is that its traversing only once. But using resultset.getString("Col 1") to resultset.getString('Col n") is showing all entries of all columns. Below is the code snippet -

ResultSet resultset = null;
ArrayList<String> arrayList = new ArrayList<String>(); 
int i = 1;
while (resultset.next()) {              
    arrayList.add(resultset.getString(i++));
    System.out.println(resultset.getString("Col 1"));
    System.out.println(resultset.getString("Col 2"));
    System.out.println(resultset.getString("Col n"));
}

唯一值 ResultSet 被复制到 ArrayList 用于第1列。然后在退出时。
但我可以看到所有列的值。
为什么？

The only value of ResultSet getting copied into ArrayList is for column 1. And then while exits. But I can see the value of all columns. Why?

推荐答案

如果我理解你的问题，有两种可能问题在这里：

If I've understood your problem correctly, there are two possible problems here:

• 结果集是 null - 我认为这不可能就像你在你的while循环中得到一个异常而没有输出任何东西


• 第二个问题是 resultset.getString（i ++）将从每个后续行
获取列1,2,3等等

• resultset is null - I assume that this cant be the case as if it was you'd get an exception in your while loop and nothing would be output
• the second problem is that resultset.getString(i++) will get columns 1,2,3 and so on from each subsequent row

我认为第二点可能是你的问题。

I think that the second point is probably your problem here.

让我们说你只返回1行，如下所示

Lets say you only had 1 row returned, as follows

Col 1, Col 2, Col3 
A    ,     B,    C

您的代码只能获得A - 它不会得到其余的列。

Your code as it stands would only get A - it wouldnt get the rest of the columns.

我建议您更改代码如下：

I suggest you change your code as follows:

ResultSet resultset = ...;
ArrayList<String> arrayList = new ArrayList<String>(); 
while (resultset.next()) {              
        int i = 1;
        while(i <= numberOfColumns) {
            arrayList.add(resultset.getString(i++));
        }
        System.out.println(resultset.getString("Col 1"));
        System.out.println(resultset.getString("Col 2"));
        System.out.println(resultset.getString("Col 3"));                    
        System.out.println(resultset.getString("Col n"));
}

修改：

获取列数：

ResultSetMetaData metadata = resultset.getMetaData();
int numberOfColumns = metadata.getColumnCount();

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