public abstract class ResultSetIterator<T> extends Object implements Iterator<T>
PreparedStatement and creates a ResultSet and
implements the Iterator interface that returns the results.
Subclasses may be created which convert a particular row into a particular type of object to be returned from the iterator.
It is intended for those ResultSets which can only iterate forward (i.e. streaming results).
On these ResultSets the aResultSet.hasNext
method cannot be called.
Therefore the ResultSet only has a next method,
but the Iterator must provide a hasNext
method which can be called an arbitrary number of times to see if there would be a next row.
The algorithm employed is to always fetch one row ahead store it in the object, so hasNext
can return if there is a next row or not. The next method then returns that previously fetched one, and
fetches the next one.
Any SQLException which are thrown from the ResultSet are assumed to be "should never happen"
type, and thus are transformed into RuntimeExceptions.
The ResultSet is opened on the first next or hasNext method, and closed at the end of the iteration. This means that an object of this type can be created then used hours later; the ResultSet will not have timed out, as the statement is executed only briefly before the results are needed.
The PreparedStatement, and the associated Connection, can also be closed at the end of the iteration if desired (if this is the only code which will be using that statement) or can be left open (if other code will use it).
Usage:
public class MyDocResultSetIterator extends ResultSetIterator<MyDoc> {
protected MyDoc objectForRow(ResultSet r) throws SQLException {
MyDoc result = new MyDoc();
result.setVal(r.getString("val"));
return result;
}
}
public Iterator<MyDoc> foo() {
PreparedStatement stat = aConnection.prepareStatement(
"SELECT val FROM big_table",
ResultSet.TYPE_FORWARD_ONLY,
ResultSet.CONCUR_READ_ONLY);
stat.setFetchSize(Integer.MIN_VALUE);
boolean shouldClosePreparedStatement = truel
return new MyDocResultSetIterator("...", stat, shouldClosePreparedStatement);
}
See Reading row-by-row into Java from MySQL.
This code has beem tested using Java 6 with MySQL 5.0 and the JDBC driver "MySQL Connector" 5.1.15.
| Modifier and Type | Class and Description |
|---|---|
static class |
ResultSetIterator.CloseStrategy |
| Constructor and Description |
|---|
ResultSetIterator(String sqlForLog,
PreparedStatement statement,
ResultSetIterator.CloseStrategy closeStrategy) |
| Modifier and Type | Method and Description |
|---|---|
boolean |
hasNext() |
T |
next() |
void |
remove() |
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitforEachRemainingpublic ResultSetIterator(String sqlForLog, PreparedStatement statement, ResultSetIterator.CloseStrategy closeStrategy)
sqlForLog - What SQL was executed? This is only used to populate the text of Exceptions