java paging dummy pages implement a simple pager

import java.util.Arrays; 
import java.util.Collections; 
import java.util.List; 
 
/** 
 * @author shuang.gao Date: 2016/1/28 Time: 12:26 
 */ 
public class Pager<T> { 
 
  /** 
   *  Number of bars per page  
   */ 
  private int pageSize; 
  /** 
   *  The original set  
   */ 
  private List<T> data; 
 
  private Pager(List<T> data, int pageSize) { 
    if (data == null || data.isEmpty()) { 
      throw new IllegalArgumentException("data must be not empty!"); 
    } 
 
    this.data = data; 
    this.pageSize = pageSize; 
  } 
 
  /** 
   *  Create a pager  
   * 
   * @param data  Data that needs to be paged  
   * @param pageSize  Number of bars per page  
   * @param <T>  The business object  
   * @return  The pager  
   */ 
  public static <T> Pager<T> create(List<T> data, int pageSize) { 
    return new Pager<>(data, pageSize); 
  } 
 
  /** 
   *  Get the paged data  
   * 
   * @param pageNum  The page number  
   * @return  Paged result  
   */ 
  public List<T> getPagedList(int pageNum) { 
    int fromIndex = (pageNum - 1) * pageSize; 
    if (fromIndex >= data.size()) { 
      return Collections.emptyList(); 
    } 
 
    int toIndex = pageNum * pageSize; 
    if (toIndex >= data.size()) { 
      toIndex = data.size(); 
    } 
    return data.subList(fromIndex, toIndex); 
  } 
 
  public int getPageSize() { 
    return pageSize; 
  } 
 
  public List<T> getData() { 
    return data; 
  } 
 
  public static void main(String[] args) { 
    Integer[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}; 
    List<Integer> list = Arrays.asList(array); 
 
    Pager<Integer> pager = Pager.create(list, 10); 
 
    List<Integer> page1 = pager.getPagedList(1); 
    System.out.println(page1); 
 
    List<Integer> page2 = pager.getPagedList(2); 
    System.out.println(page2); 
 
    List<Integer> page3 = pager.getPagedList(3); 
    System.out.println(page3); 
  } 
} 

Fake paging, as the name suggests, is not really filtering in the database, but querying from the database, getting all the results, and then doing something about it.
import java.util.Arrays;  
import java.util.Collections;  
import java.util.List;  
 
/**
  * @author shuang.gao   Date: 2016/1/28 Time: 12:26
  */  
public class Pager < T > {  
 
      /**
        * number of bars per page
        */  
      private int pageSize;  
      /**
        * original set
        */  
      private List < T > data;  
 
      private Pager(List < T > data, int pageSize) {  
              if (data == null || data.isEmpty()) {  
                      throw new IllegalArgumentException("data must be not empty!");  
              }  
 
              this.data = data;  
              this.pageSize = pageSize;  
      }  
 
      /**
        * create pagers
        *
        * @param data requires paging data
        * @param pageSize number of bars per page
        * @param < T > The business object
        * @return pager
        */  
      public static < T > Pager < T > create(List < T > data, int pageSize) {  
              return new Pager < > (data, pageSize);  
      }  
 
      /**
        * gets the paged data
        *
        * @param pageNum page number
        * @return
        */  
      public List < T > getPagedList(int pageNum) {  
              int fromIndex = (pageNum - 1) * pageSize;  
              if (fromIndex > = data.size()) {  
                      return Collections.emptyList();  
              }  
 
              int toIndex = pageNum * pageSize;  
              if (toIndex > = data.size()) {  
                      toIndex = data.size();  
              }  
              return data.subList(fromIndex, toIndex);  
      }  
 
      public int getPageSize() {  
              return pageSize;  
      }  
 
      public List < T > getData() {  
              return data;  
      }  
 
      public static void main(String[] args) {  
              Integer[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};  
              List < Integer > list = Arrays.asList(array);  
 
              Pager < Integer > pager = Pager.create(list, 10);  
 
              List < Integer > page1 = pager.getPagedList(1);  
              System.out.println(page1);  
 
              List < Integer > page2 = pager.getPagedList(2);  
              System.out.println(page2);  
 
              List < Integer > page3 = pager.getPagedList(3);  
              System.out.println(page3);  
      }  
}  
This is a simple pager, the principle is very simple, will query the data from the database, into the pager, return is a set of pages.
The advantage is that it is compatible with all JDBC databases, but the disadvantage is that this method is not suitable for large volumes of data.

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