spring-batch PostgresPagingQueryProvider 源码
spring-batch PostgresPagingQueryProvider 代码
文件路径：/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/database/support/PostgresPagingQueryProvider.java
/*
* Copyright 2006-2021 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.database.support;
import org.springframework.util.StringUtils;
/**
* Postgres implementation of a
* {@link org.springframework.batch.item.database.PagingQueryProvider} using database
* specific features.
*
* When using the groupClause, this implementation expects all select fields not used in
* aggregate functions to be included in the groupClause (the provider does not add them
* for you).
*
* @author Thomas Risberg
* @author Michael Minella
* @author Mahmoud Ben Hassine
* @since 2.0
*/
public class PostgresPagingQueryProvider extends AbstractSqlPagingQueryProvider {
@Override
public String generateFirstPageQuery(int pageSize) {
return SqlPagingQueryUtils.generateLimitSqlQuery(this, false, buildLimitClause(pageSize));
}
@Override
public String generateRemainingPagesQuery(int pageSize) {
if (StringUtils.hasText(getGroupClause())) {
return SqlPagingQueryUtils.generateLimitGroupedSqlQuery(this, buildLimitClause(pageSize));
}
else {
return SqlPagingQueryUtils.generateLimitSqlQuery(this, true, buildLimitClause(pageSize));
}
}
private String buildLimitClause(int pageSize) {
return new StringBuilder().append("LIMIT ").append(pageSize).toString();
}
@Override
public String generateJumpToItemQuery(int itemIndex, int pageSize) {
int page = itemIndex / pageSize;
int offset = (page * pageSize) - 1;
offset = offset < 0 ? 0 : offset;
String limitClause = new StringBuilder().append("LIMIT 1 OFFSET ").append(offset).toString();
return SqlPagingQueryUtils.generateLimitJumpToQuery(this, limitClause);
}
}
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