| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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 org.apache.drill.exec.store.http.paginator; |
| |
| import okhttp3.HttpUrl.Builder; |
| import org.apache.drill.common.exceptions.UserException; |
| import org.apache.drill.exec.store.http.HttpPaginatorConfig.PaginatorMethod; |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| import java.util.NoSuchElementException; |
| |
| public class OffsetPaginator extends Paginator { |
| |
| private static final Logger logger = LoggerFactory.getLogger(OffsetPaginator.class); |
| |
| private final int limit; |
| private final String limitParam; |
| private final String offsetParam; |
| private int offset; |
| |
| /** |
| * This class implements the idea of an Offset Paginator. See here for complete explanation: |
| * https://nordicapis.com/everything-you-need-to-know-about-api-pagination/ |
| * <p> |
| * |
| * @param builder The okhttp3 URL builder which has the API root URL |
| * @param limit The limit clause from the sql query |
| * @param pageSize The page size from the API documentation. To minimize requests, it should be set to the max that the API allows. |
| * @param limitParam The field name which corresponds to the limit field from the API |
| * @param offsetParam The field name which corresponds to the offset field from the API |
| */ |
| public OffsetPaginator(Builder builder, int limit, int pageSize, String limitParam, String offsetParam) { |
| super(builder, PaginatorMethod.OFFSET, pageSize, limit); |
| this.limit = limit; |
| this.limitParam = limitParam; |
| this.offsetParam = offsetParam; |
| this.offset = 0; |
| |
| // Page size must be greater than zero |
| if (pageSize <= 0) { |
| throw UserException |
| .validationError() |
| .message("API page size must be a positive integer.") |
| .build(logger); |
| } |
| } |
| |
| @Override |
| public boolean hasNext() { |
| return !partialPageReceived && (limit < 0 || offset < limit); |
| } |
| |
| @Override |
| public String next() { |
| if (!hasNext()) { |
| throw new NoSuchElementException(); |
| } |
| |
| builder.removeAllEncodedQueryParameters(offsetParam); |
| builder.removeAllEncodedQueryParameters(limitParam); |
| |
| builder.addQueryParameter(offsetParam, String.valueOf(offset)); |
| builder.addQueryParameter(limitParam, String.valueOf(pageSize)); |
| offset += pageSize; |
| |
| return builder.build().url().toString(); |
| } |
| } |