com.metamx.common.collect.MoreIterators Maven / Gradle / Ivy
/*
* Copyright 2011,2012 Metamarkets Group Inc.
*
* 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.metamx.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;
}
}
}
}