Java tutorial
/* * #%L * Alfresco Repository * %% * Copyright (C) 2005 - 2016 Alfresco Software Limited * %% * This file is part of the Alfresco software. * If the software was purchased under a paid Alfresco license, the terms of * the paid license agreement will prevail. Otherwise, the software is * provided under the following open source license terms: * * Alfresco is free software: you can redistribute it and/or modify * it under the terms of the GNU Lesser General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * Alfresco is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with Alfresco. If not, see <http://www.gnu.org/licenses/>. * #L% */ package org.alfresco.repo.virtual.page; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.Comparator; import java.util.LinkedList; import java.util.List; import org.alfresco.query.PagingRequest; import org.alfresco.query.PagingResults; import org.alfresco.util.Pair; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * A generic utility for arranging a {@link List} of objects of type * <code>R</code> into a <code>R</code> objects page obtained from a * {@link PagingResultsSource} considering a given {@link PagingRequest} for the * resulted {@link PagingResults}. * * @author Bogdan Horje * @param <R> */ public class PageCollator<R> { private static Log logger = LogFactory.getLog(PageCollator.class); /** * Implementors are paging request capable objects - i.e. can provide * data-paged results of type <code>R</code> considering a given * {@link PagingRequest}. * * @param <R> */ public interface PagingResultsSource<R> { PagingResults<R> retrieve(PagingRequest pr) throws PageCollationException; } /** * @param objects * @param objectPageSurce * @param pagingRequest * @param comparator * @return a {@link PagingResults} R objects obtained from merging a * collection of R objects with a paged result obtained from a * {@link PagingResultsSource} considering the a merged result * {@link PagingRequest} * @throws PageCollationException */ public PagingResults<R> collate(List<R> objects, PagingResultsSource<R> objectPageSurce, PagingRequest pagingRequest, Comparator<R> comparator) throws PageCollationException { final int skip = pagingRequest.getSkipCount(); final int pageSize = pagingRequest.getMaxItems(); if (skip < 0 || pageSize < 0) { throw new InvalidPageBounds("Negative page skip index and/or bounds."); } int preemptiveSkip = Math.max(0, skip - objects.size()); int pageSkip = skip - preemptiveSkip; int preemptiveSize = pageSize + pageSkip; PagingResults<R> pageResults = null; try { PagingRequest preemptiveRequest = new PagingRequest(preemptiveSkip, preemptiveSize, pagingRequest.getQueryExecutionId()); preemptiveRequest.setRequestTotalCountMax(pagingRequest.getRequestTotalCountMax()); pageResults = objectPageSurce.retrieve(preemptiveRequest); } catch (InvalidPageBounds e) { if (logger.isDebugEnabled()) { logger.debug(e); } pageResults = new PagingResults<R>() { @Override public List<R> getPage() { return Collections.emptyList(); } @Override public boolean hasMoreItems() { return false; } @Override public Pair<Integer, Integer> getTotalResultCount() { return new Pair<Integer, Integer>(null, null); } @Override public String getQueryExecutionId() { return null; } }; } return collate(objects, pageResults, pageSkip, pagingRequest, comparator); } private PagingResults<R> collate(List<R> objects, final PagingResults<R> objectPageSurce, int pageSkip, final PagingRequest pagingRequest, Comparator<R> comparator) { final int pageSize = pagingRequest.getMaxItems(); final List<R> inPageList = objectPageSurce.getPage(); final List<R> collatedPageList = new LinkedList<>(); final boolean endOfCollation = collate(objects, inPageList, pageSkip, pageSize, comparator, collatedPageList); final int resultsSize = objects.size(); final Pair<Integer, Integer> pageTotal = objectPageSurce.getTotalResultCount(); Integer pageTotalFirst = null; Integer pageTotalSecond = null; if (pageTotal != null) { pageTotalFirst = pageTotal.getFirst(); pageTotalSecond = pageTotal.getSecond(); } final Pair<Integer, Integer> total = new Pair<>( pageTotalFirst == null ? null : pageTotalFirst + resultsSize, pageTotalSecond == null ? null : pageTotalSecond + resultsSize); final boolean hasMoreItems = objectPageSurce.hasMoreItems() || !endOfCollation; return new PagingResults<R>() { @Override public List<R> getPage() { return collatedPageList; } @Override public boolean hasMoreItems() { return hasMoreItems; } @Override public Pair<Integer, Integer> getTotalResultCount() { return total; } @Override public String getQueryExecutionId() { return pagingRequest.getQueryExecutionId(); } }; } private boolean collate(List<R> objects, List<R> pageObjects, int pageSkip, int pageSize, Comparator<R> comparator, List<R> collatedResult) { final int resultsSize = objects.size(); final int inPageSize = pageObjects.size(); if (pageSkip >= resultsSize + inPageSize) { return true; } List<R> collation = new ArrayList<>(objects.size() + pageObjects.size()); collation.addAll(pageObjects); for (int i = 0; i < resultsSize; i++) { final int collationSize = collation.size(); final R result = objects.get(i); int j = 0; if (comparator != null) { for (; j < collationSize; j++) { final R collated = collation.get(j); if (comparator.compare(result, collated) <= 0) { break; } } } collation.add(j, result); } final R[] collationArray = (R[]) collation.toArray(); final int zeroPageSize = (pageSize == 0 ? collationArray.length - pageSkip : pageSize); final int to = Math.min(pageSkip + zeroPageSize, collationArray.length); collatedResult.addAll(Arrays.asList(Arrays.copyOfRange(collationArray, pageSkip, to))); return to == collationArray.length; } }