001/* 002 * Copyright 2006-2018 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.batch.item; 018 019import org.springframework.lang.Nullable; 020 021/** 022 * Strategy interface for providing the data. <br> 023 * 024 * Implementations are expected to be stateful and will be called multiple times 025 * for each batch, with each call to {@link #read()} returning a different value 026 * and finally returning <code>null</code> when all input data is exhausted.<br> 027 * 028 * Implementations need <b>not</b> be thread-safe and clients of a {@link ItemReader} 029 * need to be aware that this is the case.<br> 030 * 031 * A richer interface (e.g. with a look ahead or peek) is not feasible because 032 * we need to support transactions in an asynchronous batch. 033 * 034 * @author Rob Harrop 035 * @author Dave Syer 036 * @author Lucas Ward 037 * @author Mahmoud Ben Hassine 038 * @since 1.0 039 */ 040public interface ItemReader<T> { 041 042 /** 043 * Reads a piece of input data and advance to the next one. Implementations 044 * <strong>must</strong> return <code>null</code> at the end of the input 045 * data set. In a transactional setting, caller might get the same item 046 * twice from successive calls (or otherwise), if the first call was in a 047 * transaction that rolled back. 048 * 049 * @throws ParseException if there is a problem parsing the current record 050 * (but the next one may still be valid) 051 * @throws NonTransientResourceException if there is a fatal exception in 052 * the underlying resource. After throwing this exception implementations 053 * should endeavour to return null from subsequent calls to read. 054 * @throws UnexpectedInputException if there is an uncategorised problem 055 * with the input data. Assume potentially transient, so subsequent calls to 056 * read might succeed. 057 * @throws Exception if an there is a non-specific error. 058 * @return T the item to be processed or {@code null} if the data source is 059 * exhausted 060 */ 061 @Nullable 062 T read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException; 063 064}