CODEWITHSUNDEEP
javasqlarraylistprepared-statementresultset
Joey Hipolito
Joey Hipolito

Reputation: 3166

returning an arraylist of arraylist from a resultset in java

I created a database wrapper class in java and created a method called 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:

[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?

How can I achieve something like this

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

Upvotes: 2

Views: 27254

Answers (2)

user3328044
user3328044

Reputation: 1

    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");
    }

Upvotes: 0

jlordo
jlordo

Reputation: 37823

Like this:

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
}

Upvotes: 7

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