org.springframework.batch.item.support.SingleItemPeekableItemReader Maven / Gradle / Ivy
/*
* Copyright 2006-2019 the original author or authors.
*
* 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
*
* https://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.springframework.batch.item.support;
import java.util.Map.Entry;
import org.springframework.batch.item.ExecutionContext;
import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.ItemStream;
import org.springframework.batch.item.ItemStreamException;
import org.springframework.batch.item.ItemStreamReader;
import org.springframework.batch.item.ParseException;
import org.springframework.batch.item.PeekableItemReader;
import org.springframework.batch.item.UnexpectedInputException;
import org.springframework.lang.Nullable;
/**
*
* A {@link PeekableItemReader} that allows the user to peek one item ahead.
* Repeated calls to {@link #peek()} will return the same item, and this will be
* the next item returned from {@link #read()}.
*
*
*
* Intentionally not thread-safe: it wouldn't be possible to honour the peek in
* multiple threads because only one of the threads that peeked would get that
* item in the next call to read.
*
*
* @author Dave Syer
*
*/
public class SingleItemPeekableItemReader implements ItemStreamReader, PeekableItemReader {
private ItemReader delegate;
private T next;
private ExecutionContext executionContext = new ExecutionContext();
/**
* The item reader to use as a delegate. Items are read from the delegate
* and passed to the caller in {@link #read()}.
*
* @param delegate the delegate to set
*/
public void setDelegate(ItemReader delegate) {
this.delegate = delegate;
}
/**
* Get the next item from the delegate (whether or not it has already been
* peeked at).
*
* @see ItemReader#read()
*/
@Nullable
@Override
public T read() throws Exception, UnexpectedInputException, ParseException {
if (next != null) {
T item = next;
next = null;
// executionContext = new ExecutionContext();
return item;
}
return delegate.read();
}
/**
* Peek at the next item, ensuring that if the delegate is an
* {@link ItemStream} the state is stored for the next call to
* {@link #update(ExecutionContext)}.
*
* @return the next item (or null if there is none).
*
* @see PeekableItemReader#peek()
*/
@Nullable
@Override
public T peek() throws Exception, UnexpectedInputException, ParseException {
if (next == null) {
updateDelegate(executionContext);
next = delegate.read();
}
return next;
}
/**
* If the delegate is an {@link ItemStream}, just pass the call on,
* otherwise reset the peek cache.
*
* @throws ItemStreamException if there is a problem
* @see ItemStream#close()
*/
@Override
public void close() throws ItemStreamException {
next = null;
if (delegate instanceof ItemStream) {
((ItemStream) delegate).close();
}
executionContext = new ExecutionContext();
}
/**
* If the delegate is an {@link ItemStream}, just pass the call on,
* otherwise reset the peek cache.
*
* @param executionContext the current context
* @throws ItemStreamException if there is a problem
* @see ItemStream#open(ExecutionContext)
*/
@Override
public void open(ExecutionContext executionContext) throws ItemStreamException {
next = null;
if (delegate instanceof ItemStream) {
((ItemStream) delegate).open(executionContext);
}
executionContext = new ExecutionContext();
}
/**
* If there is a cached peek, then retrieve the execution context state from
* that point. If there is no peek cached, then call directly to the
* delegate.
*
* @param executionContext the current context
* @throws ItemStreamException if there is a problem
* @see ItemStream#update(ExecutionContext)
*/
@Override
public void update(ExecutionContext executionContext) throws ItemStreamException {
if (next != null) {
// Get the last state from the delegate instead of using
// current value.
for (Entry entry : this.executionContext.entrySet()) {
executionContext.put(entry.getKey(), entry.getValue());
}
return;
}
updateDelegate(executionContext);
}
private void updateDelegate(ExecutionContext executionContext) {
if (delegate instanceof ItemStream) {
((ItemStream) delegate).update(executionContext);
}
}
}