org.springframework.batch.item.data.AbstractPaginatedDataItemReader Maven / Gradle / Ivy
/*
* Copyright 2013 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.data;
import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.ItemStreamReader;
import org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader;
import org.springframework.util.Assert;
import java.util.Iterator;
/**
* A base class that handles basic reading logic based on the paginated
* semantics of Spring Data's paginated facilities. It also handles the
* semantics required for restartability based on those facilities.
*
* @author Michael Minella
* @author Glenn Renfro
* @since 2.2
* @param Type of item to be read
*/
public abstract class AbstractPaginatedDataItemReader extends
AbstractItemCountingItemStreamItemReader {
protected volatile int page = 0;
protected int pageSize = 10;
protected Iterator results;
private Object lock = new Object();
/**
* The number of items to be read with each page.
*
* @param pageSize the number of items. pageSize must be greater than zero.
*/
public void setPageSize(int pageSize) {
Assert.isTrue(pageSize > 0, "pageSize must be greater than zero");
this.pageSize = pageSize;
}
@Override
protected T doRead() throws Exception {
synchronized (lock) {
if(results == null || !results.hasNext()) {
results = doPageRead();
page ++;
if(results == null || !results.hasNext()) {
return null;
}
}
if(results.hasNext()) {
return results.next();
}
else {
return null;
}
}
}
/**
* Method this {@link ItemStreamReader} delegates to
* for the actual work of reading a page. Each time
* this method is called, the resulting {@link Iterator}
* should contain the items read within the next page.
*
* If the {@link Iterator} is empty or null when it is
* returned, this {@link ItemReader} will assume that the
* input has been exhausted.
*
* @return an {@link Iterator} containing the items within a page.
*/
protected abstract Iterator doPageRead();
@Override
protected void doOpen() throws Exception {
}
@Override
protected void doClose() throws Exception {
}
@Override
protected void jumpToItem(int itemLastIndex) throws Exception {
synchronized (lock) {
page = itemLastIndex / pageSize;
int current = itemLastIndex % pageSize;
Iterator initialPage = doPageRead();
for(; current >= 0; current--) {
initialPage.next();
}
}
}
}