从java中的结果集返回arraylist的arraylist

Question

我在java中创建了一个数据库包装类,并创建了一个名为的方法fetchAll(query).

this.openConnection();

ArrayList<String> results = new ArrayList<String>();
PreparedStatement stmt = this.conn.prepareStatement(query);
ResultSet resultset = stmt.executeQuery();

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

while (resultset.next()) {
    int i = 1;
    while (i < numcols) {
        results.add(resultset.getString(i++));
    }
}

this.closeConnection();

return results;

现在它返回如下内容:

[1, name1, address1, age1, 2, name2, address2, age2, 2, name2, address2, age3]

我发现奇怪而且方法没有返回所有列,它缺少1列,为什么呢？

我怎样才能实现这样的目标

[
  [1,name1,address1,age1,bday1],
  [2,name2,address2,age2,bday2],
  [3,name3,address3,age3,bday3]
]

Answer 1

像这样:

List<List<String>> result = new ArrayList<>();  // List of list, one per row
...
while (resultset.next()) {
    List<String> row = new ArrayList<>(numcols); // new list per row
    int i = 1;
    while (i <= numcols) {  // don't skip the last column, use <=
        row.add(resultset.getString(i++));
    }
    result.add(row); // add it to the result
}