com.speedment.runtime.core.internal.stream.StreamUtil Maven / Gradle / Ivy
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/**
*
* Copyright (c) 2006-2019, Speedment, Inc. All Rights Reserved.
*
* 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.
*/
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package com.speedment.runtime.core.internal.stream;
import com.speedment.runtime.core.db.SqlFunction;
import com.speedment.runtime.core.exception.SpeedmentException;
import com.speedment.runtime.core.stream.parallel.ParallelStrategy;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.*;
import java.util.function.Consumer;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import static com.speedment.runtime.core.util.StaticClassUtil.instanceNotAllowed;
import static java.util.Objects.requireNonNull;
/**
*
* @author Emil Forslund
*/
public final class StreamUtil {
public static Stream streamOfOptional(@SuppressWarnings("OptionalUsedAsFieldOrParameterType") Optional element) {
return Stream.of(element.orElse(null)).filter(Objects::nonNull);
}
public static Stream streamOfNullable(T element) {
// Needless to say, element is nullable...
if (element == null) {
return Stream.empty();
} else {
return Stream.of(element);
}
}
public static Stream asStream(Iterator iterator) {
requireNonNull(iterator);
return asStream(iterator, false);
}
public static Stream asStream(Iterator iterator, boolean parallel) {
requireNonNull(iterator);
final Iterable iterable = () -> iterator;
return StreamSupport.stream(iterable.spliterator(), parallel);
}
public static Stream asStream(ResultSet resultSet, SqlFunction mapper) {
return asStream(resultSet, mapper, ParallelStrategy.computeIntensityDefault());
}
public static Stream asStream(ResultSet resultSet, SqlFunction mapper, ParallelStrategy parallelStrategy) {
requireNonNull(resultSet);
requireNonNull(mapper);
final Iterator iterator = new ResultSetIterator<>(resultSet, mapper);
return StreamSupport.stream(parallelStrategy.spliteratorUnknownSize(iterator, Spliterator.IMMUTABLE + Spliterator.NONNULL), false);
}
public static Stream from(@SuppressWarnings("OptionalUsedAsFieldOrParameterType") Optional optional) {
requireNonNull(optional);
return optional.map(Stream::of).orElseGet(Stream::empty);
}
/**
* Specialized read-only {@link Iterator} for consuming
* {@link ResultSet ResultSets} by mapping them to an entity using an
* adapter. This implementation is not thread safe.
*
* @param the type of the entity
*/
static class ResultSetIterator implements Iterator {
/**
* The current state of the {@code ResultSetIterator}.
*/
private enum State {
/**
* There is a row in the ResultSet that has not yet been consumed.
*/
NEXT,
/**
* There are no more rows in the ResultSet.
*/
NO_NEXT,
/**
* The current row has already been consumed and we don't know if
* there are any more yet. Call {@link #hasNext()} to find out.
*/
NOT_DETERMINED
}
private final ResultSet resultSet;
private final SqlFunction mapper;
private State state = State.NOT_DETERMINED;
ResultSetIterator(final ResultSet resultSet,
final SqlFunction mapper) {
this.resultSet = requireNonNull(resultSet);
this.mapper = requireNonNull(mapper);
}
/**
* {@inheritDoc}
*
* After the termination of this method, the state will be either
* {@link State#NEXT} or {@link State#NO_NEXT}. Calling this method
* multiple times in a row has no effect. The state will remain the
* same.
*
* @return if there are more rows
*/
@Override
public boolean hasNext() {
switch (state) {
case NEXT : return true;
case NO_NEXT : return false;
case NOT_DETERMINED : {
try {
if (!resultSet.next()) {
state = State.NO_NEXT;
return false;
}
} catch (final SQLException ex) {
state = State.NO_NEXT;
return false;
}
state = State.NEXT;
return true;
}
default : throw new IllegalStateException(
"Unknown state '" + state + "'."
);
}
}
@Override
public T next() {
if (state == State.NOT_DETERMINED) {
if (!hasNext()) {
throwNoSuchElementException();
};
}
if (state == State.NO_NEXT) {
throwNoSuchElementException();
}
state = State.NOT_DETERMINED;
try {
return mapper.apply(resultSet);
} catch (final SQLException ex) {
throw new SpeedmentException(ex);
}
}
@Override
public void forEachRemaining(Consumer action) {
if (state == State.NOT_DETERMINED) {
if (!hasNext()) {
return;
};
}
if (state == State.NO_NEXT) {
return;
}
try {
do {
try {
action.accept(mapper.apply(resultSet));
} catch (final SQLException ex) {
throw new SpeedmentException(ex);
}
} while (resultSet.next());
} catch (final SQLException ex) {
// Do nothing.
} finally {
state = State.NO_NEXT;
}
}
private void throwNoSuchElementException() {
throw new NoSuchElementException(
"Next was called even though hasNext() returned false."
);
}
}
/**
* Utility classes should not be instantiated.
*/
private StreamUtil() {
instanceNotAllowed(getClass());
}
}