/**
* Copyright 1999-2015 dangdang.com.
*
* 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 com.dangdang.ddframe.rdb.sharding.merger.component.reducer;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import com.dangdang.ddframe.rdb.sharding.exception.ShardingJdbcException;
import com.dangdang.ddframe.rdb.sharding.jdbc.adapter.AbstractReducerResultSetAdapter;
import com.dangdang.ddframe.rdb.sharding.merger.component.ReducerResultSet;
import com.dangdang.ddframe.rdb.sharding.merger.row.OrderByRow;
import com.dangdang.ddframe.rdb.sharding.parser.result.merger.OrderByColumn;
import com.google.common.base.Predicate;
import com.google.common.collect.Collections2;
import lombok.extern.slf4j.Slf4j;
/**
* 流式排序.
*
* @author gaohongtao
*/
@Slf4j
public class StreamingOrderByReducerResultSet extends AbstractReducerResultSetAdapter implements ReducerResultSet {
private final List orderByColumns;
private boolean initial;
private Queue effectiveResultSetQueue;
public StreamingOrderByReducerResultSet(final List orderByColumns) {
this.orderByColumns = orderByColumns;
}
@Override
public void init(final List preResultSet) throws SQLException {
input(preResultSet);
setDelegate(preResultSet.get(0));
effectiveResultSetQueue = new LinkedList<>(Collections2.filter(preResultSet, new Predicate() {
@Override
public boolean apply(final ResultSet input) {
try {
return input.next();
} catch (final SQLException ex) {
throw new ShardingJdbcException(ex);
}
}
}));
log.trace("Effective result set:{}", effectiveResultSetQueue);
}
@Override
public boolean next() throws SQLException {
if (initial) {
nextEffectiveResultSets();
} else {
initial = true;
}
OrderByRow chosenOrderByValue = null;
for (ResultSet each : effectiveResultSetQueue) {
OrderByRow eachOrderByValue = new OrderByRow(orderByColumns, each);
if (null == chosenOrderByValue || chosenOrderByValue.compareTo(eachOrderByValue) > 0) {
chosenOrderByValue = eachOrderByValue;
setDelegate(each);
}
}
if (!effectiveResultSetQueue.isEmpty()) {
log.trace(toString());
}
return !effectiveResultSetQueue.isEmpty();
}
private void nextEffectiveResultSets() throws SQLException {
boolean next = getDelegate().next();
if (!next) {
effectiveResultSetQueue.remove(getDelegate());
log.trace("Result set {} finish", getDelegate());
}
}
@Override
public String toString() {
return String.format("Current result set:%s", getDelegate());
}
}