pageable.java

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/*
 * Copyright (c) 2003-2006, Simon Brown
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in
 *     the documentation and/or other materials provided with the
 *     distribution.
 *
 *   - Neither the name of Pebble nor the names of its contributors may
 *     be used to endorse or promote products derived from this software
 *     without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package net.sourceforge.pebble.util;

import java.util.List;

/**
 * Helper class that implements paging over a collection.
 *
 * @author    Simon Brown
 */
public class Pageable<T> {

  /** the default page size */
  public static final int DEFAULT_PAGE_SIZE = 10;

  private static final int PAGE_WINDOW = 10;

  /** the list over which this class is paging */
  private List<T> list;

  /** the page size */
  private int pageSize = DEFAULT_PAGE_SIZE;

  /** the current page */
  private int page;

  /** the starting index */
  private int startingIndex;

  /** the ending index */
  private int endingIndex;

  /** the maximum number of pages */
  private int maxPages;

  /**
   * Creates a new instance with the specified list.
   *
   * @param list    a List
   */
  public Pageable(List<T> list) {
    this.list = list;
    this.page = 1;
    this.maxPages = 1;

    calculatePages();
  }

  private void calculatePages() {
    if (pageSize > 0) {
      // calculate how many pages there are
      if (list.size() % pageSize == 0) {
        maxPages = list.size() / pageSize;
      } else {
        maxPages = (list.size() / pageSize) + 1;
      }
    }
  }

  /**
   * Gets the list that this instance is paging over.
   *
   * @return  a List
   */
  public List<T> getList() {
    return this.list;
  }

  /**
   * Gets the subset of the list for the current page.
   *
   * @return  a List
   */
  public List<T> getListForPage() {
    return list.subList(startingIndex, endingIndex);
  }

  /**
   * Gets the page size.
   *
   * @return  the page size as an int
   */
  public int getPageSize() {
    return this.pageSize;
  }

  /**
   * Sets the page size.
   *
   * @param pageSize   the page size as an int
   */
  public void setPageSize(int pageSize) {
    this.pageSize = pageSize;
    calculatePages();
  }

  /**
   * Gets the page.
   *
   * @return  the page as an int
   */
  public int getPage() {
    return this.page;
  }

  /**
   * Sets the page size.
   *
   * @param p    the page as an int
   */
  public void setPage(int p) {
    if (p >= maxPages) {
      this.page = maxPages;
    } else if (p <= 1) {
      this.page = 1;
    } else {
      this.page = p;
    }

    // now work out where the sub-list should start and end
    startingIndex = pageSize * (page-1);
    if (startingIndex < 0) {
      startingIndex = 0;
    }
    endingIndex = startingIndex + pageSize;
    if (endingIndex > list.size()) {
      endingIndex = list.size();
    }
  }

  /**
   * Gets the maximum number of pages.
   *
   * @return  the maximum number of pages as an int
   */
  public int getMaxPages() {
    return this.maxPages;
  }

  /**
   * Determines whether there is a previous page and gets the page number.
   *
   * @return  the previous page number, or zero
   */
  public int getPreviousPage() {
    if (page > 1) {
      return page-1;
    } else {
      return 0;
    }
  }

  /**
   * Determines whether there is a next page and gets the page number.
   *
   * @return  the next page number, or 0
   */
  public int getNextPage() {
    if (page < maxPages) {
      return page+1;
    } else {
      return 0;
    }
  }

  /**
   * Gets the minimum page in the window.
   *
   * @return  the page number
   */
  public int getMinPageRange() {
    if (getPage() > PAGE_WINDOW) {
      return getPage() - PAGE_WINDOW;
    } else {
      return 1;
    }
  }

  /**
   * Gets the maximum page in the window.
   *
   * @return  the page number
   */
  public int getMaxPageRange() {
    if (getPage() < (getMaxPages() - PAGE_WINDOW)) {
      return getPage() + PAGE_WINDOW;
    } else {
      return getMaxPages();
    }
  }

}