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RESOLVED - issue BATCH-1347: Restartable look-ahead (peekable) ItemReader

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dsyer
2009-11-18 07:45:15 +00:00
parent d67b9d7101
commit c7bb8ae1a8
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49
spring-batch-infrastructure/src/main/java/org/springframework/batch/item/PeekableItemReader.java Normal file
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/*
* Copyright 2006-2010 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
*
* 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.springframework.batch.item;
/**
* <p>
* A specialisation of {@link ItemReader} that allows the user to look ahead
* into the stream of items. This is useful, for instance, when reading flat
* file data that contains record separator lines which are actually part of the
* next record.
* </p>
*
* <p>
* The detailed contract for {@link #peek()} has to be defined by the
* implementation because there is no general way to define it in a concurrent
* environment. The definition of "the next read()" operation is tenuous if
* multiple clients are reading concurrently, and the ability to peek implies
* that some state is likely to be stored, so implementations of
* {@link PeekableItemReader} may well be restricted to single threaded use.
* </p>
*
* @author Dave Syer
*
*/
public interface PeekableItemReader<T> extends ItemReader<T> {
/**
* Get the next item that would be returned by {@link #read()}, without
* affecting the result of {@link #read()}.
*
* @return the next item
* @throws Exception if there is a problem
*/
T peek() throws Exception, UnexpectedInputException, ParseException;
}

155
spring-batch-infrastructure/src/main/java/org/springframework/batch/item/support/SingleItemPeekableItemReader.java Normal file
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/*
* Copyright 2006-2010 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
*
* 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.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;
/**
* <p>
* 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()}.
* </p>
*
* <p>
* 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.
* </p>
*
* @author Dave Syer
*
*/
public class SingleItemPeekableItemReader<T> implements ItemStreamReader<T>, PeekableItemReader<T> {
private ItemReader<T> 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<T> delegate) {
this.delegate = delegate;
}
/**
* Get the next item from the delegate (whether or not it has already been
* peeked at).
*
* @see ItemReader#read()
*/
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()
*/
@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()
*/
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)
*/
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)
*/
public void update(ExecutionContext executionContext) throws ItemStreamException {
if (next != null) {
// Get the last state from the delegate instead of using
// current value.
for (Entry<String, Object> 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);
}
}
}

135
spring-batch-infrastructure/src/test/java/org/springframework/batch/item/support/SingleItemPeekableItemReaderTests.java Normal file
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/*
* Copyright 2006-2010 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
*
* 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.springframework.batch.item.support;
import static org.junit.Assert.assertEquals;
import java.util.Arrays;
import java.util.List;
import org.junit.Test;
import org.springframework.batch.item.ExecutionContext;
/**
* @author Dave Syer
*
*/
public class SingleItemPeekableItemReaderTests {
private SingleItemPeekableItemReader<String> reader = new SingleItemPeekableItemReader<String>();
/**
* Test method for {@link org.springframework.batch.item.support.SingleItemPeekableItemReader#read()}.
*/
@Test
public void testRead() throws Exception {
reader.setDelegate(new CountingListItemReader<String>(Arrays.asList("a", "b")));
assertEquals("a", reader.read());
assertEquals("b", reader.read());
assertEquals(null, reader.read());
}
/**
* Test method for {@link org.springframework.batch.item.support.SingleItemPeekableItemReader#peek()}.
*/
@Test
public void testPeek() throws Exception {
reader.setDelegate(new CountingListItemReader<String>(Arrays.asList("a", "b")));
assertEquals("a", reader.peek());
assertEquals("a", reader.read());
assertEquals("b", reader.read());
assertEquals(null, reader.peek());
assertEquals(null, reader.read());
}
/**
* Test method for {@link org.springframework.batch.item.support.SingleItemPeekableItemReader#close()}.
*/
@Test
public void testCloseAndOpenNoPeek() throws Exception {
reader.setDelegate(new CountingListItemReader<String>(Arrays.asList("a", "b")));
assertEquals("a", reader.read());
ExecutionContext executionContext = new ExecutionContext();
reader.update(executionContext);
reader.close();
reader.open(executionContext);
assertEquals("b", reader.read());
}
/**
* Test method for {@link org.springframework.batch.item.support.SingleItemPeekableItemReader#close()}.
*/
@Test
public void testCloseAndOpenWithPeek() throws Exception {
reader.setDelegate(new CountingListItemReader<String>(Arrays.asList("a", "b", "c")));
assertEquals("a", reader.read());
assertEquals("b", reader.peek());
ExecutionContext executionContext = new ExecutionContext();
reader.update(executionContext);
reader.close();
reader.open(executionContext);
assertEquals("b", reader.read());
}
@Test
public void testCloseAndOpenWithPeekAndRead() throws Exception {
ExecutionContext executionContext = new ExecutionContext();
reader.setDelegate(new CountingListItemReader<String>(Arrays.asList("a", "b", "c")));
assertEquals("a", reader.read());
assertEquals("b", reader.peek());
reader.update(executionContext);
reader.close();
reader.open(executionContext);
assertEquals("b", reader.read());
assertEquals("c", reader.peek());
reader.update(executionContext);
reader.close();
reader.open(executionContext);
assertEquals("c", reader.read());
}
public static class CountingListItemReader<T> extends AbstractItemCountingItemStreamItemReader<T> {
private final List<T> list;
private int counter = 0;
public CountingListItemReader(List<T> list) {
this.list = list;
setName("foo");
}
@Override
protected void doClose() throws Exception {
counter = 0;
}
@Override
protected void doOpen() throws Exception {
counter = 0;
}
@Override
protected T doRead() throws Exception {
if (counter>=list.size()) {
return null;
}
return list.get(counter++);
}
}
}