kafka AbstractIterator 源码
kafka AbstractIterator 代码
文件路径：/clients/src/main/java/org/apache/kafka/common/utils/AbstractIterator.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF 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 org.apache.kafka.common.utils;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* A base class that simplifies implementing an iterator
* @param <T> The type of thing we are iterating over
*/
public abstract class AbstractIterator<T> implements Iterator<T> {
private enum State {
READY, NOT_READY, DONE, FAILED
}
private State state = State.NOT_READY;
private T next;
@Override
public boolean hasNext() {
switch (state) {
case FAILED:
throw new IllegalStateException("Iterator is in failed state");
case DONE:
return false;
case READY:
return true;
default:
return maybeComputeNext();
}
}
@Override
public T next() {
if (!hasNext())
throw new NoSuchElementException();
state = State.NOT_READY;
if (next == null)
throw new IllegalStateException("Expected item but none found.");
return next;
}
@Override
public void remove() {
throw new UnsupportedOperationException("Removal not supported");
}
public T peek() {
if (!hasNext())
throw new NoSuchElementException();
return next;
}
protected T allDone() {
state = State.DONE;
return null;
}
protected abstract T makeNext();
private Boolean maybeComputeNext() {
state = State.FAILED;
next = makeNext();
if (state == State.DONE) {
return false;
} else {
state = State.READY;
return true;
}
}
}
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