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;
}
Minor optimization, if you don't really want to create any new list at all.
/**
* returns a view (not a new list) of the sourceList for the
* range based on page and pageSize
* @param sourceList
* @param page, page number should start from 1
* @param pageSize
* @return
* custom error can be given instead of returning emptyList
*/
public static <T> List<T> getPage(List<T> sourceList, int page, int pageSize) {
if(pageSize <= 0 || page <= 0) {
throw new IllegalArgumentException("invalid page size: " + pageSize);
}
int fromIndex = (page - 1) * pageSize;
if(sourceList == null || sourceList.size() <= fromIndex){
return Collections.emptyList();
}
// toIndex exclusive
return sourceList.subList(fromIndex, Math.min(fromIndex + pageSize, sourceList.size()));
}