de.m0ep.canvas.Pagination.java Source code

Introduction

Here is the source code for de.m0ep.canvas.Pagination.java

Source

/*
 * The MIT License (MIT) Copyright  2013 Florian Mller
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the Software?), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED AS IS?, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package de.m0ep.canvas;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import org.apache.http.client.methods.HttpGet;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Strings;
import com.google.gson.JsonArray;

import de.m0ep.canvas.exceptions.CanvasLmsException;

/**
 * Class to navigate through canvas pagination
 * 
 * @author Florian Mller
 * 
 * @param <T>
 *            Ressource type
 */
public class Pagination<T> implements Iterable<List<T>> {
    private static final Logger LOG = LoggerFactory.getLogger(Pagination.class);

    /**
     * Pagination iterator to iterate through pages.
     * 
     * @author Florian Mller
     */
    protected class PaginationIterator implements Iterator<List<T>> {
        private Pagination<T> pagination;
        private boolean initialPage = false;

        public PaginationIterator(Pagination<T> pagination) {
            this.pagination = pagination;
            this.initialPage = true;
        }

        @Override
        public boolean hasNext() {
            if (initialPage) {
                return true;
            }

            return pagination.hasNext();
        }

        @Override
        public List<T> next() {
            if (initialPage) {
                initialPage = false;
                return pagination.getData();
            }

            if (!pagination.hasNext()) {
                throw new NoSuchElementException("No further pages to fetch.");
            }

            pagination = pagination.fetchNextPage();
            return pagination.getData();
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException(
                    "Remove is not supported by " + PaginationIterator.class.getSimpleName());
        }
    }

    private final CanvasLmsClient client;
    private final Class<T> paginationType;
    private final String nextURL;
    private final List<T> data;

    /**
     * Constructs a new {@link Pagination}.
     * 
     * @param client
     *            The {@link CanvasLmsClient}.
     * @param json
     *            The JSON data.
     * @param next
     *            The URI to the next page.
     * @param paginationType
     *            The class of the data in <code>json</code> parameter.
     */
    public Pagination(final CanvasLmsClient client, final String json, final String next,
            final Class<T> paginationType) {
        this.paginationType = paginationType;
        this.client = client;
        this.nextURL = next;

        JsonArray array = client.getGson().fromJson(json, JsonArray.class);
        List<T> pageItems = new ArrayList<T>();
        for (int i = 0; i < array.size(); i++) {
            pageItems.add(client.getGson().fromJson(array.get(i), paginationType));
        }

        this.data = Collections.unmodifiableList(pageItems);
    }

    @Override
    public Iterator<List<T>> iterator() {
        return new PaginationIterator(this);
    }

    /**
     * Fetch the next page of this pagination
     * 
     * @return A new {@link Pagination} for the next page.
     */
    public Pagination<T> fetchNextPage() {
        LOG.info("Fetch next page {}.", getNextURL());
        try {
            CanvasLmsRequest<T> request = new CanvasLmsRequest<T>(client, HttpGet.class, getNextURL() + "",
                    paginationType) {
            };
            request.setOauthToken(client.getOAuthToken());

            return request.executePagination();
        } catch (CanvasLmsException e) {
            throw new RuntimeException(e);
        }
    }

    public String getNextURL() {
        return nextURL;
    }

    public List<T> getData() {
        return data;
    }

    public boolean hasNext() {
        return !Strings.isNullOrEmpty(nextURL);
    }
}