DelegatingSystemTablesProvider.java
/*
* 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.facebook.presto.connector.system;
import com.facebook.presto.spi.ConnectorSession;
import com.facebook.presto.spi.SchemaTableName;
import com.facebook.presto.spi.SystemTable;
import com.google.common.collect.ImmutableList;
import java.util.List;
import java.util.Optional;
import java.util.Set;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.collect.ImmutableSet.toImmutableSet;
import static com.google.common.collect.MoreCollectors.toOptional;
import static java.util.Objects.requireNonNull;
public class DelegatingSystemTablesProvider
implements SystemTablesProvider
{
private final List<SystemTablesProvider> delegates;
public DelegatingSystemTablesProvider(SystemTablesProvider... delegates)
{
this(ImmutableList.copyOf(delegates));
}
public DelegatingSystemTablesProvider(List<SystemTablesProvider> delegates)
{
requireNonNull(delegates, "delegates is null");
checkArgument(delegates.size() >= 1, "empty delegates");
this.delegates = ImmutableList.copyOf(delegates);
}
@Override
public Set<SystemTable> listSystemTables(ConnectorSession session)
{
return delegates.stream()
.flatMap(delegate -> delegate.listSystemTables(session).stream())
.collect(toImmutableSet());
}
@Override
public Optional<SystemTable> getSystemTable(ConnectorSession session, SchemaTableName tableName)
{
return delegates.stream()
.map(delegate -> delegate.getSystemTable(session, tableName))
.filter(Optional::isPresent)
// this ensures there is 0 or 1 element in stream
.map(Optional::get)
.collect(toOptional());
}
}