org.sonar.server.db.ResultSetIterator.java Source code

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Here is the source code for org.sonar.server.db.ResultSetIterator.java

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/*
 * SonarQube, open source software quality management tool.
 * Copyright (C) 2008-2014 SonarSource
 * mailto:contact AT sonarsource DOT com
 *
 * SonarQube 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.
 *
 * SonarQube 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.server.db;

import org.apache.commons.dbutils.DbUtils;

import javax.annotation.CheckForNull;

import java.io.Closeable;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * 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
    @CheckForNull
    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);
        }
    }
}