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/*
* SonarQube
* Copyright (C) 2009-2016 SonarSource SA
* mailto:contact AT sonarsource DOT com
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
package org.sonar.db;
import java.io.Closeable;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.commons.dbutils.DbUtils;
/**
* Forward-only {@link java.util.Iterator} over a {@link java.sql.ResultSet}. Rows are
* lazily loaded. The underlying ResultSet must be closed by calling the method
* {@link #close()}
* <p/>
* As a safeguard, the ResultSet is automatically closed after the last element has
* been retrieved via {@link #next()} or {@link #hasNext()} is called (which will return false).
* This automagic behavior is not enough to remove explicit calls to {@link #close()}
* from caller methods. Errors raised before end of traversal must still be handled.
*/
public abstract class ResultSetIterator<E> implements Iterator<E>, Closeable {
private final ResultSet rs;
private final PreparedStatement stmt;
private volatile boolean didNext = false;
private volatile boolean hasNext = false;
private volatile boolean closed = false;
public ResultSetIterator(PreparedStatement stmt) throws SQLException {
this.stmt = stmt;
this.rs = stmt.executeQuery();
}
protected ResultSetIterator(ResultSet rs) {
this.stmt = null;
this.rs = rs;
}
@Override
public boolean hasNext() {
if (closed) {
return false;
}
if (!didNext) {
hasNext = doNextQuietly();
if (hasNext) {
didNext = true;
} else {
close();
}
}
return hasNext;
}
@Override
public E next() {
if (!hasNext()) {
close();
throw new NoSuchElementException();
}
try {
return read(rs);
} catch (SQLException e) {
throw new IllegalStateException("Fail to read result set row", e);
} finally {
hasNext = doNextQuietly();
if (!hasNext) {
close();
}
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public void close() {
closed = true;
DbUtils.closeQuietly(rs);
DbUtils.closeQuietly(stmt);
}
protected abstract E read(ResultSet rs) throws SQLException;
private boolean doNextQuietly() {
try {
return rs.next();
} catch (SQLException e) {
throw new IllegalStateException("Fail to read row of JDBC result set", e);
}
}
}
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