tech.simter.data.Page Maven / Gradle / Ivy
package tech.simter.data;
import java.io.Serializable;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.function.Consumer;
/**
* A page is a sublist of a list of objects.
* It allows gain information about the position of it in the containing entire list.
*
* The main interface methods just 4 of below, all other method can be calculate from them:
*
* - int getNumber() - The page number, it's one of the page conditions
* - int getCapacity() - The page capacity, it's the maximal size of each page, it's one of the page conditions
* - int getRows() - All real row data of this page, it's one of the page results
* - int getTotalCount() - The total amount of all data store in the repository, it's one of the page results
*
*
* @param the type of the row data
* @author RJ 2017-04-27
*/
public interface Page extends Serializable, Iterable {
/**
* The default page capacity.
*/
int DEFAULT_CAPACITY = 25;
/**
* The number of this page. It's minimal value is 1.
*
* @return the number of this page
*/
int getNumber();
/**
* The maximal size of each page. It's minimal value is 1.
*
* @return the maximal size of each page
*/
int getCapacity();
/**
* All the row data of this page.
* Returns {@link Collections#emptyList()} if this page has no data. Implementer should never return null.
*
* @return all the real row data of this page
*/
List getRows();
/**
* The total amount of all rows in the store.
*
* @return zero if the repository has no data
*/
long getTotalCount();
/**
* The number of total pages. It's minimal value is 0.
*
* @return zero if the repository has no data
*/
int getPageCount();
/**
* The offset to be taken according to the page number and capacity. It's minimal value is 0.
*
* @return The offset to be taken according to the page number and capacity
*/
int getOffset();
/**
* Whether the page has data at all.
*
* @return true if this page has data, otherwise return false
*/
boolean isEmpty();
/**
* The real data size of this page. It's minimal value is 0.
*
* @return the real data size of this page
*/
int getSize();
/**
* Whether the current page is the first page.
*
* @return true if this page is the first page, otherwise return false
*/
boolean isFirst();
/**
* Whether the current page is the last page.
*
* @return true if this page is the last page, otherwise return false
*/
boolean isLast();
/**
* Build a new page instance.
*
* @param number the page number
* @param capacity the page maximal size
* @param rows the page data
* @param totalCount the total amount of all rows in the store
* @param the type of the row data
* @return the page instance holds the data
*/
static Page build(int number, int capacity, List rows, long totalCount) {
// Make this class can not be reached from outside.
class PageImpl implements Page {
private int number;
private int capacity;
private List rows;
private long totalCount;
private PageImpl(int number, int capacity, List rows, long totalCount) {
this.number = Math.max(1, number);
this.capacity = toValidCapacity(capacity);
this.rows = rows != null ? Collections.unmodifiableList(rows) : Collections.emptyList();
this.totalCount = Math.max(0, totalCount);
}
@Override
public int getNumber() {
return number;
}
@Override
public int getCapacity() {
return capacity;
}
@Override
public List getRows() {
return rows;
}
@Override
public long getTotalCount() {
return totalCount;
}
@Override
public int getPageCount() {
return (int) Math.ceil((double) totalCount / (double) capacity);
}
@Override
public int getOffset() {
return (number - 1) * capacity;
}
@Override
public boolean isEmpty() {
return rows.isEmpty();
}
@Override
public int getSize() {
return rows.size();
}
@Override
public boolean isFirst() {
return number <= 1;
}
@Override
public boolean isLast() {
return number + 1 > getPageCount();
}
// implement the {@link Iterable} interface
@Override
public Iterator iterator() {
return rows.iterator();
}
@Override
public void forEach(Consumer action) {
Objects.requireNonNull(action);
for (TT t : this.getRows()) {
action.accept(t);
}
}
}
return new PageImpl<>(number, capacity, rows, totalCount);
}
/**
* Calculate the offset value
*
* @param number the page number, default to 1 if less then 1
* @param capacity the page capacity, default to {@link Page#DEFAULT_CAPACITY} if less then 1
* @return the offset value, it's minimal value is zero
*/
static int calculateOffset(int number, int capacity) {
number = Math.max(1, number);
capacity = toValidCapacity(capacity);
return (number - 1) * capacity;
}
/**
* Convert the specific capacity to a valid value.
* If the specific capacity less then 1, return {@link Page#DEFAULT_CAPACITY}, otherwise return the specific capacity.
*
* @param capacity the specific capacity
* @return a valid capacity
*/
static int toValidCapacity(int capacity) {
return capacity < 1 ? DEFAULT_CAPACITY : capacity;
}
}