io.druid.java.util.common.collect.MoreIterators Maven / Gradle / Ivy
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* Licensed to Metamarkets Group Inc. (Metamarkets) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. Metamarkets licenses this file
* to you 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 io.druid.java.util.common.collect;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class MoreIterators
{
public static Iterator bracket(final Iterator iterator, final Runnable before, final Runnable after)
{
return before(after(iterator, after), before);
}
/**
* Run f immediately before the first element of iterator is generated.
* Exceptions raised by f will prevent the requested behavior on the
* underlying iterator, and can be handled by the caller.
*/
public static Iterator before(final Iterator iterator, final Runnable f)
{
return new Iterator()
{
private final Runnable fOnlyOnce = new RunOnlyOnce(f);
@Override
public boolean hasNext()
{
fOnlyOnce.run();
return iterator.hasNext();
}
@Override
public X next()
{
fOnlyOnce.run();
return iterator.next();
}
@Override
public void remove()
{
fOnlyOnce.run();
iterator.remove();
}
};
}
/**
* Run f immediately after the last element of iterator is generated.
* Exceptions must not be raised by f.
*/
public static Iterator after(final Iterator iterator, final Runnable f)
{
return new Iterator()
{
private final Runnable fOnlyOnce = new RunOnlyOnce(f);
@Override
public boolean hasNext()
{
final boolean hasNext = iterator.hasNext();
if (!hasNext) {
fOnlyOnce.run();
}
return hasNext;
}
@Override
public X next()
{
try {
return iterator.next();
}
catch (NoSuchElementException e) {
fOnlyOnce.run(); // (f exceptions are prohibited because they destroy e here)
throw e;
}
}
@Override
public void remove()
{
iterator.remove();
}
};
}
private static class RunOnlyOnce implements Runnable
{
private final Runnable f;
private volatile boolean hasRun = false;
public RunOnlyOnce(Runnable f)
{
this.f = f;
}
@Override
public void run()
{
if (!hasRun) {
f.run();
hasRun = true;
}
}
}
}