/*
* Copyright (c) the original 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 com.complexible.stardog.ext.spring.batch;
import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.batch.item.ItemReader;
import org.springframework.batch.item.NonTransientResourceException;
import org.springframework.batch.item.ParseException;
import org.springframework.batch.item.UnexpectedInputException;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import com.complexible.stardog.ext.spring.DataSource;
import com.complexible.stardog.ext.spring.RowMapper;
import com.complexible.stardog.ext.spring.SnarlTemplate;
/**
* Implementation of a Spring Batch ItemReader that supports the SNARL API
*
* @author Al Baker
* @author Clark & Parsia
*
* @param <T>
*
*/
public class SnarlItemReader<T> implements ItemReader<T>, InitializingBean, DisposableBean {
final Logger log = LoggerFactory.getLogger(SnarlItemReader.class);
private SnarlTemplate snarlTemplate;
private DataSource dataSource;
private List<T> results;
private String query;
private RowMapper<T> rowMapper;
/*
* Some explanation on this method: in Spring Batch, ItemReader is stateful for the life of
* a Batch run, and will be called repeatedly until exhausted and returns null. There is
* an 'ItemStream' interface that provides an open, close, and update method for managing a
* cursor based approach for reading. However, this includes an execution context since Spring
* Batch manages execution state for things like retries and restarts.
*
* For the initial implementation - will keep a simple implementation with Stardog where the
* result set is read out and then read out one at a time by Spring Batch. Therefore, any Spring
* Batch retries, or persisting job state to disk, will include the results sets instead of a cursor.
*
* The rationale for this is to keep the batch system simple as Stardog moves to 1.0 and keeping
* Stardog connections (ie the cursor) around in Spring Batch will be a post 1.0 refactoring.
*
* (non-Javadoc)
* @see org.springframework.batch.item.ItemReader#read()
*/
@Override
public T read() throws Exception, UnexpectedInputException, ParseException,
NonTransientResourceException {
if (results == null) {
results = snarlTemplate.query(query, rowMapper);
log.debug("SnarlItemReader finished loading query data");
}
if (results.size() > 0) {
return results.remove(0);
} else {
return null;
}
}
@Override
public void afterPropertiesSet() throws Exception {
snarlTemplate = new SnarlTemplate();
snarlTemplate.setDataSource(dataSource);
}
@Override
public void destroy() throws Exception {
snarlTemplate.setDataSource(null);
snarlTemplate = null;
}
/**
* @return the dataSource
*/
public DataSource getDataSource() {
return dataSource;
}
/**
* @param dataSource the dataSource to set
*/
public void setDataSource(DataSource dataSource) {
this.dataSource = dataSource;
}
/**
* @return the query
*/
public String getQuery() {
return query;
}
/**
* @param query the query to set
*/
public void setQuery(String query) {
this.query = query;
}
/**
* @return the rowMapper
*/
public RowMapper<T> getRowMapper() {
return rowMapper;
}
/**
* @param rowMapper the rowMapper to set
*/
public void setRowMapper(RowMapper<T> rowMapper) {
this.rowMapper = rowMapper;
}
}