PaginationUtil.java

package io.github.jhipster.sample.web.rest.util;

/*-
 * #%L
 * Jhipster Sample Application
 * %%
 * Copyright (C) 2017 Osgiliath
 * %%
 * 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
 * 
 *      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.
 * #L%
 */

import org.springframework.data.domain.Page;
import org.springframework.http.HttpHeaders;
import org.springframework.web.util.UriComponentsBuilder;

/**
 * Utility class for handling pagination.
 *
 * <p>
 * Pagination uses the same principles as the <a href="https://developer.github.com/v3/#pagination">GitHub API</a>,
 * and follow <a href="http://tools.ietf.org/html/rfc5988">RFC 5988 (Link header)</a>.
 */
public final class PaginationUtil {

    private PaginationUtil() {
    }

    public static HttpHeaders generatePaginationHttpHeaders(Page page, String baseUrl) {

        HttpHeaders headers = new HttpHeaders();
        headers.add("X-Total-Count", Long.toString(page.getTotalElements()));
        String link = "";
        if ((page.getNumber() + 1) < page.getTotalPages()) {
            link = "<" + generateUri(baseUrl, page.getNumber() + 1, page.getSize()) + ">; rel=\"next\",";
        }
        // prev link
        if ((page.getNumber()) > 0) {
            link += "<" + generateUri(baseUrl, page.getNumber() - 1, page.getSize()) + ">; rel=\"prev\",";
        }
        // last and first link
        int lastPage = 0;
        if (page.getTotalPages() > 0) {
            lastPage = page.getTotalPages() - 1;
        }
        link += "<" + generateUri(baseUrl, lastPage, page.getSize()) + ">; rel=\"last\",";
        link += "<" + generateUri(baseUrl, 0, page.getSize()) + ">; rel=\"first\"";
        headers.add(HttpHeaders.LINK, link);
        return headers;
    }

    private static String generateUri(String baseUrl, int page, int size) {
        return UriComponentsBuilder.fromUriString(baseUrl).queryParam("page", page).queryParam("size", size).toUriString();
    }
}