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 */ 016package org.springframework.batch.item; 017 018import org.springframework.lang.Nullable; 019 020/** 021 * <p> 022 * A specialisation of {@link ItemReader} that allows the user to look ahead 023 * into the stream of items. This is useful, for instance, when reading flat 024 * file data that contains record separator lines which are actually part of the 025 * next record. 026 * </p> 027 * 028 * <p> 029 * The detailed contract for {@link #peek()} has to be defined by the 030 * implementation because there is no general way to define it in a concurrent 031 * environment. The definition of "the next read()" operation is tenuous if 032 * multiple clients are reading concurrently, and the ability to peek implies 033 * that some state is likely to be stored, so implementations of 034 * {@link PeekableItemReader} may well be restricted to single threaded use. 035 * </p> 036 * 037 * @author Dave Syer 038 * @author Mahmoud Ben Hassine 039 * 040 */ 041public interface PeekableItemReader<T> extends ItemReader<T> { 042 043 /** 044 * Get the next item that would be returned by {@link #read()}, without 045 * affecting the result of {@link #read()}. 046 * 047 * @return the next item or {@code null} if the data source is exhausted 048 * @throws Exception if there is a problem 049 */ 050 @Nullable 051 T peek() throws Exception, UnexpectedInputException, ParseException; 052 053}