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Lightweight multi-platform REST
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/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.httprpc.sql;

import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.NoSuchElementException;

/**
 * Class that presents the contents of a result set as an iterable sequence
 * of maps.
 */
public class ResultSetAdapter implements Iterable> {
    private ResultSet resultSet;
    private ResultSetMetaData resultSetMetaData;

    private LinkedHashMap row = new LinkedHashMap<>();

    /**
     * Creates a new result set adapter.
     *
     * @param resultSet
     * The source result set.
     */
    public ResultSetAdapter(ResultSet resultSet) {
        if (resultSet == null) {
            throw new IllegalArgumentException();
        }

        this.resultSet = resultSet;

        try {
            resultSetMetaData = resultSet.getMetaData();
        } catch (SQLException exception) {
            throw new RuntimeException(exception);
        }
    }

    @Override
    public Iterator> iterator() {
        return new Iterator>() {
            private Boolean hasNext = null;

            @Override
            public boolean hasNext() {
                if (hasNext == null) {
                    try {
                        hasNext = resultSet.next() ? Boolean.TRUE : Boolean.FALSE;
                    } catch (SQLException exception) {
                        throw new RuntimeException(exception);
                    }
                }

                return hasNext.booleanValue();
            }

            @Override
            public Map next() {
                if (!hasNext()) {
                    throw new NoSuchElementException();
                }

                row.clear();

                try {
                    for (int i = 0, n = resultSetMetaData.getColumnCount(); i < n; i++) {
                        row.put(resultSetMetaData.getColumnLabel(i + 1), resultSet.getObject(i + 1));
                    }
                } catch (SQLException exception) {
                    throw new RuntimeException(exception);
                }

                hasNext = null;

                return row;
            }
        };
    }
}