Custom Pagination by Array List

Custom pagination by array list

I SOLVED with this workaround.

    import org.springframework.data.domain.Sort;
    import org.springframework.data.domain.PageRequest;
    import org.springframework.data.domain.Page;
    import org.springframework.data.domain.PageImpl;
    import org.springframework.data.domain.Sort.Direction;
    ...    

        int page = 0;
        int count = 8;
        String sortOrder = "desc";
        String sortBy = "id";

        Sort sort = new Sort(Direction.fromString(sortOrder), sortBy);
        PageRequest pageable = new PageRequest(page, count, sort);

        List<Impianto> impiantos = myService.findMyMethod(); // returned 30 objects 
        int max = (count*(page+1)>impiantos.size())? impiantos.size(): count*(page+1);

        Page<Impianto> pageImpianto = new PageImpl<Impianto>(impiantos.subList(page*count, max), pageable, impiantos.size());  

and I implemented a new custom comparator class

import java.lang.reflect.Field;
import java.util.Comparator;
import java.util.Date;

public class MyListComparator implements Comparator<Object> {

    final String sortBy;
    final String sortOrder;

    public MyListComparator(String sortBy, String sortOrder) {
        this.sortBy = sortBy;
        this.sortOrder = sortOrder;
    }

    @Override
    public int compare(Object o1, Object o2) {

        try {
            Field field1 = o1.getClass().getDeclaredField(sortBy);
            Field field2 = o2.getClass().getDeclaredField(sortBy);

            field1.setAccessible(true); // because the fields in Impianto entity has "private" 
            field2.setAccessible(true);

            if(o1.getClass().getDeclaredField(sortBy).getType() == Long.class){
                Long d1 = (Long) field1.get(o1);
                Long d2 = (Long) field2.get(o2);
                return (sortOrder.toLowerCase().equals("asc"))? d1.compareTo(d2) : d2.compareTo(d1);

            }else if(o1.getClass().getDeclaredField(sortBy).getType() == Date.class){
                Date d1 = (Date) field1.get(o1);
                Date d2 = (Date) field2.get(o2);
                return (sortOrder.toLowerCase().equals("asc"))? d1.compareTo(d2) : d2.compareTo(d1);

            }else{
                String d1 = (String) field1.get(o1);
                String d2 = (String) field2.get(o2);
                return (sortOrder.toLowerCase().equals("asc"))? d1.compareTo(d2) : d2.compareTo(d1);

            }
        } catch (SecurityException e) {
            throw new RuntimeException(e);
        } catch (NoSuchFieldException e) {
            throw new RuntimeException("Missing variable sortBy");
        }catch (ClassCastException e) {
            throw new RuntimeException("sortBy is not found in class list");
        } catch (IllegalArgumentException e) {
            //shoud not happen
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }


}

Paginating an ArrayList

I would do it like this:

I'm not sure what renderValues does, and whether we have to substract 1 or maybe defaultStep from the upper bound of the moveCounter.

private void pageMove (int step)
{
    moveCounter = moveCounter + step;
    if (moveCounter < 0) moveCounter = 0;
    if (moveCounter > values.size ()) moveCounter = values.size ();
    renderValues (currentIndex, false);
}

private void pageNext ()
{
    pageMove (defaultStep);
}

private void pagePrevious ()
{
    pageMove (-defaultStep);
}

The first 3 lines could be packed into two big ternary experssions like so:

mc = ((mc + s) < 0) ? 0 : ((mc + s) > vs) ? vs : (mc + s); 

but the 3 lines solution is better to follow.

Pagination From ArrayList in Android

try this

ArrayList<ItemCategory> arraylistsub = new ArrayList<>(Constant.arrayListCategories.subList(0,10));

How to implement pagination on a list?

I've solved this before. I made a static getPages method that breaks a generic collection into a list of pages (which are also lists). I've provided the code below.

public static <T> List<List<T>> getPages(Collection<T> c, Integer pageSize) {
    if (c == null)
        return Collections.emptyList();
    List<T> list = new ArrayList<T>(c);
    if (pageSize == null || pageSize <= 0 || pageSize > list.size())
        pageSize = list.size();
    int numPages = (int) Math.ceil((double)list.size() / (double)pageSize);
    List<List<T>> pages = new ArrayList<List<T>>(numPages);
    for (int pageNum = 0; pageNum < numPages;)
        pages.add(list.subList(pageNum * pageSize, Math.min(++pageNum * pageSize, list.size())));
    return pages;
}

How to create a pagination function with a given list

def paginator(array, page_number):
    n, remainder = page_number, len(array) % page_number
    curr, idx, old_idx = 1, 0, 0
    while n + remainder != 0:
        idx += len(array) // page_number + bool(remainder)
        print(f"this is page {curr} have object {array[old_idx:idx]}")
        n -= 1
        remainder = max(remainder - 1, 0)
        curr += 1
        old_idx = idx


lst = list(range(1, 10))
page_number = 4

paginator(lst, page_number)

Prints:

this is page 1 have object [1, 2, 3]
this is page 2 have object [4, 5]
this is page 3 have object [6, 7]
this is page 4 have object [8, 9]

Java how to transform List<Object> to Page from JPA pagination

When you do custom queries and want to use Pageable, it's up to you to implement a logic to create a paging for your result list. In your case you aren't doing that so it's probably (you said it isn't working, but didn't say what isn't working so I can only guess) just returning the entire result list without paging applied.

A simple solution would be to use sublist and use the result of that operation as your parameter for PageImpl. Big problem is that you are still getting the entire result list from the database in the background which creates uneceassary overhead.

You could also adjust your query using

em.createQuery(query.where(predicate))
      .setFirstResult(offset)
     .setMaxResults(limit)
     .getResultList()

Now the paging is done in the database which is a lot better.

Or you save yourself some trouble and use Springs Specification interface instead of creating your own search method.

First your CarRepository needs to extend JpaSpecificationExecutor. Now spring will generate a findAll(Specification, Pageable) method for your repository.

Second step is to create your search specification:

public class SearchSpecification implements Specification<Car> {
    private final String brand;
    private final String model
    private final String type
    private final Integer registrationYear
    private final String color
    private final String fuel
    private final String transmission
    private final String doors
    private final double price

    // constructor & maybe getter
    public Predicate toPredicate(Root<Car> root, CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder) {
        // Create your search predicate
    }
}

Now you can simply call carRepository.findAll(new SearchSpecification (/* parameters */), pageable); and spring does the paging for you.

Paginate Javascript array

You can use Array.prototype.slice and just supply the params for (start, end).

function paginate(array, page_size, page_number) {  // human-readable page numbers usually start with 1, so we reduce 1 in the first argument  return array.slice((page_number - 1) * page_size, page_number * page_size);}
console.log(paginate([1, 2, 3, 4, 5, 6], 2, 2));console.log(paginate([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], 4, 1));

$menuItems = array_slice( $menuItems, 0, 10 ); 

$menuItems = array_slice( $menuItems, 10, 10 );

$page = ! empty( $_GET['page'] ) ? (int) $_GET['page'] : 1;
$total = count( $yourDataArray ); //total items in array    
$limit = 20; //per page    
$totalPages = ceil( $total/ $limit ); //calculate total pages
$page = max($page, 1); //get 1 page when $_GET['page'] <= 0
$page = min($page, $totalPages); //get last page when $_GET['page'] > $totalPages
$offset = ($page - 1) * $limit;
if( $offset < 0 ) $offset = 0;

$yourDataArray = array_slice( $yourDataArray, $offset, $limit );

$link = 'index.php?page=%d';
$pagerContainer = '<div style="width: 300px;">';   
if( $totalPages != 0 ) 
{
  if( $page == 1 ) 
  { 
    $pagerContainer .= ''; 
  } 
  else 
  { 
    $pagerContainer .= sprintf( '<a href="' . $link . '" style="color: #c00"> « prev page</a>', $page - 1 ); 
  }
  $pagerContainer .= ' <span> page <strong>' . $page . '</strong> from ' . $totalPages . '</span>'; 
  if( $page == $totalPages ) 
  { 
    $pagerContainer .= ''; 
  }
  else 
  { 
    $pagerContainer .= sprintf( '<a href="' . $link . '" style="color: #c00"> next page » </a>', $page + 1 ); 
  }           
}                   
$pagerContainer .= '</div>';

echo $pagerContainer;