/*
* Copyright 2014 NAVER Corp.
*
* 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.navercorp.pinpoint.common.util;
import java.util.Enumeration;
/**
* @author emeroad
*/
public class DelegateEnumeration<E> implements Enumeration<E> {
private static final Object NULL_OBJECT = new Object();
private final Enumeration<E> delegate;
private final Filter<E> filter;
private boolean hasMoreElements;
private E nextElement;
private Exception nextException;
private static final Filter SKIP_FILTER = new Filter() {
@Override
public boolean filter(Object o) {
return false;
}
};
@SuppressWarnings("unchecked")
public DelegateEnumeration(Enumeration<E> delegate) {
this(delegate, SKIP_FILTER);
}
public DelegateEnumeration(Enumeration<E> delegate, Filter<E> filter) {
this.delegate = delegate;
this.filter = filter;
}
@Override
public boolean hasMoreElements() {
next(true);
return hasMoreElements;
}
@Override
public E nextElement() {
next(false);
// nextException
if (nextException != null) {
final Exception exception = this.nextException;
clearNext();
this.<RuntimeException>throwException(exception);
}
// nextResult
final E result = getNextElement();
clearNext();
return result;
}
private void clearNext() {
this.nextException = null;
this.nextElement = null;
}
private E getNextElement() {
if (nextElement == NULL_OBJECT) {
return null;
}
return nextElement;
}
@SuppressWarnings("unchecked")
private <T extends Exception> void throwException(final Exception exception) throws T {
throw (T) exception;
}
private void next(final boolean hasMoreElementMethod) {
if (nextElement != null || nextException != null) {
return;
}
while (true) {
final boolean nextExist = delegate.hasMoreElements();
if (!nextExist && hasMoreElementMethod) {
this.hasMoreElements = false;
return;
}
// error emulation
E nextElement;
try {
nextElement = delegate.nextElement();
} catch (Exception e) {
this.hasMoreElements = nextExist;
this.nextException = e;
break;
}
if (filter.filter(nextElement)) {
continue;
}
this.hasMoreElements = nextExist;
if (nextElement == null) {
this.nextElement = (E) NULL_OBJECT;
} else {
this.nextElement = nextElement;
}
break;
}
}
// for Test
Exception _getNextException() {
return nextException;
}
public interface Filter<E> {
boolean filter(E e);
}
}