001/* 002 * Copyright 2006-2012 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.database.support; 018 019import org.springframework.util.StringUtils; 020 021/** 022 * Postgres implementation of a {@link org.springframework.batch.item.database.PagingQueryProvider} using database specific features. 023 * 024 * When using the groupClause, this implementation expects all select fields not used in aggregate functions to be included in the 025 * groupClause (the provider does not add them for you). 026 * 027 * @author Thomas Risberg 028 * @author Michael Minella 029 * @since 2.0 030 */ 031public class PostgresPagingQueryProvider extends AbstractSqlPagingQueryProvider { 032 033 @Override 034 public String generateFirstPageQuery(int pageSize) { 035 return SqlPagingQueryUtils.generateLimitSqlQuery(this, false, buildLimitClause(pageSize)); 036 } 037 038 @Override 039 public String generateRemainingPagesQuery(int pageSize) { 040 if(StringUtils.hasText(getGroupClause())) { 041 return SqlPagingQueryUtils.generateLimitGroupedSqlQuery(this, true, buildLimitClause(pageSize)); 042 } 043 else { 044 return SqlPagingQueryUtils.generateLimitSqlQuery(this, true, buildLimitClause(pageSize)); 045 } 046 } 047 048 private String buildLimitClause(int pageSize) { 049 return new StringBuilder().append("LIMIT ").append(pageSize).toString(); 050 } 051 052 @Override 053 public String generateJumpToItemQuery(int itemIndex, int pageSize) { 054 int page = itemIndex / pageSize; 055 int offset = (page * pageSize) - 1; 056 offset = offset<0 ? 0 : offset; 057 String limitClause = new StringBuilder().append("LIMIT 1 OFFSET ").append(offset).toString(); 058 return SqlPagingQueryUtils.generateLimitJumpToQuery(this, limitClause); 059 } 060 061}