从java中的结果集中返回arraylist的arraylist
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returning an arraylist of arraylist from a resultset in java
提问by Joey Hipolito
I created a database wrapper class in java and created a method called fetchAll(query).
我在 java 中创建了一个数据库包装器类并创建了一个名为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;
Now it returns something like this:
现在它返回如下内容：
[1, name1, address1, age1, 2, name2, address2, age2, 2, name2, address2, age3]
Which I found odd and the method does not return all columns, it lacks 1 column, why is it?
我发现这很奇怪，并且该方法没有返回所有列，它缺少 1 列，这是为什么？
How can I achieve something like this
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]
]
采纳答案by jlordo
Like this:
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
}
回答by user3328044
ResultSet resultset = statement.executeQuery(sql);//from DB
int numcols = resultset.getMetaData().getColumnCount();
List <List <String> > result = new ArrayList<>();
while (resultset.next()) {
List <String> row = new ArrayList<>(numcols); // new list per row
for (int i=1; i<= numcols; i++) { // don't skip the last column, use <=
row.add(resultset.getString(i));
System.out.print(resultset.getString(i) + "\t");
}
result.add(row); // add it to the result
System.out.print("\n");
}
