PagedListHolder 这个类可以 对分页操作进行封装
文件在：import org.springframework.beans.support.PagedListHolder;下
默认是把查出来的所有信息，根据设置的每页多少条显示，然后分割成若干个List集合，并显示出来。如果是小规模的分页，此方法用起来还是非常方便的。
如果是大规模的分页数据，那就非常影响效率。
演示DEMO：
package test;
import java.util.Iterator;
import java.util.List;
import org.springframework.beans.support.PagedListHolder;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import entity.News;
import biz.NewsBiz;
public class Test123 {
public static void main(String[] args) {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(
new String[] { "context-ioc.xml" });
NewsBiz news = (NewsBiz) context.getBean("newsBiz");
List list = news.findAll();
PagedListHolder pagedList = new PagedListHolder(list);
// 设置每页显示的数量
pagedList.setPageSize(5);
int i = 1;
while (true) {
Iterator it = pagedList.getPageList().iterator();
System.out.println("第" + i + "页");
// 显示每页的内容
while (it.hasNext()) {
System.out.println(((News) it.next()).getNtitle());
}
// 如果是末页,则退出
if (pagedList.isLastPage()) {
break;
}
// 跳转到下一页
pagedList.nextPage();
i++;
}
}
}
在SPRING中：
//全部新闻
public ModelAndView all(HttpServletRequest request,HttpServletResponse response){
newsList = newsBiz.findAll();
if (newsList!=null && !newsList.isEmpty()) {
//mv.addObject("newsList", newsList);
PagedListHolder<News> newsPageList = new PagedListHolder<News>(newsList);
//设置每页显示的数量5
newsPageList.setPageSize(5);
List<News> newsList = newsPageList.getPageList();
mv.addObject("newsList", newsList);
}else {
mv.addObject("newsMsg", "暂无任何新闻！");
}
mv.setViewName("/WEB-INF/news/all.jsp");
return mv;
}
在JSP中：
<c:forEach items="${newsList}" var="nlist" varStatus="vs">
<tr>
<td>${nlist.sort.stname}</td>
<td><a href="news.do?method=info&nid=${nlist.nid}" target="_blank">${nlist.ntitle}</a></td>
<td><fmt:formatDate value="${nlist.ntime}" pattern="yyyy/MM/dd HH:mm"/></td></tr>
<tr>
</c:forEach>
PagedListHolder.java源码：
/*
* Copyright 2002-2012 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.beans.support;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import org.springframework.util.Assert;
/**
* PagedListHolder is a simple state holder for handling lists of objects,
* separating them into pages. Page numbering starts with 0.
*
* <p>This is mainly targetted at usage in web UIs. Typically, an instance will be
* instantiated with a list of beans, put into the session, and exported as model.
* The properties can all be set/get programmatically, but the most common way will
* be data binding, i.e. populating the bean from request parameters. The getters
* will mainly be used by the view.
*
* <p>Supports sorting the underlying list via a {@link SortDefinition} implementation,
* available as property "sort". By default, a {@link MutableSortDefinition} instance
* will be used, toggling the ascending value on setting the same property again.
*
* <p>The data binding names have to be called "pageSize" and "sort.ascending",
* as expected by BeanWrapper. Note that the names and the nesting syntax match
* the respective JSTL EL expressions, like "myModelAttr.pageSize" and
* "myModelAttr.sort.ascending".
*
* @author Juergen Hoeller
* @since 19.05.2003
* @see #getPageList()
* @see org.springframework.beans.support.MutableSortDefinition
*/
@SuppressWarnings("serial")
public class PagedListHolder<E> implements Serializable {
public static final int DEFAULT_PAGE_SIZE = 10;
public static final int DEFAULT_MAX_LINKED_PAGES = 10;
private List<E> source;
private Date refreshDate;
private SortDefinition sort;
private SortDefinition sortUsed;
private int pageSize = DEFAULT_PAGE_SIZE;
private int page = 0;
private boolean newPageSet;
private int maxLinkedPages = DEFAULT_MAX_LINKED_PAGES;
/**
* Create a new holder instance.
* You'll need to set a source list to be able to use the holder.
* @see #setSource
*/
public PagedListHolder() {
this(new ArrayList<E>(0));
}
/**
* Create a new holder instance with the given source list, starting with
* a default sort definition (with "toggleAscendingOnProperty" activated).
* @param source the source List
* @see MutableSortDefinition#setToggleAscendingOnProperty
*/
public PagedListHolder(List<E> source) {
this(source, new MutableSortDefinition(true));
}
/**
* Create a new holder instance with the given source list.
* @param source the source List
* @param sort the SortDefinition to start with
*/
public PagedListHolder(List<E> source, SortDefinition sort) {
setSource(source);
setSort(sort);
}
/**
* Set the source list for this holder.
*/
public void setSource(List<E> source) {
Assert.notNull(source, "Source List must not be null");
this.source = source;
this.refreshDate = new Date();
this.sortUsed = null;
}
/**
* Return the source list for this holder.
*/
public List<E> getSource() {
return this.source;
}
/**
* Return the last time the list has been fetched from the source provider.
*/
public Date getRefreshDate() {
return this.refreshDate;
}
/**
* Set the sort definition for this holder.
* Typically an instance of MutableSortDefinition.
* @see org.springframework.beans.support.MutableSortDefinition
*/
public void setSort(SortDefinition sort) {
this.sort = sort;
}
/**
* Return the sort definition for this holder.
*/
public SortDefinition getSort() {
return this.sort;
}
/**
* Set the current page size.
* Resets the current page number if changed.
* <p>Default value is 10.
*/
public void setPageSize(int pageSize) {
if (pageSize != this.pageSize) {
this.pageSize = pageSize;
if (!this.newPageSet) {
this.page = 0;
}
}
}
/**
* Return the current page size.
*/
public int getPageSize() {
return this.pageSize;
}
/**
* Set the current page number.
* Page numbering starts with 0.
*/
public void setPage(int page) {
this.page = page;
this.newPageSet = true;
}
/**
* Return the current page number.
* Page numbering starts with 0.
*/
public int getPage() {
this.newPageSet = false;
if (this.page >= getPageCount()) {
this.page = getPageCount() - 1;
}
return this.page;
}
/**
* Set the maximum number of page links to a few pages around the current one.
*/
public void setMaxLinkedPages(int maxLinkedPages) {
this.maxLinkedPages = maxLinkedPages;
}
/**
* Return the maximum number of page links to a few pages around the current one.
*/
public int getMaxLinkedPages() {
return this.maxLinkedPages;
}
/**
* Return the number of pages for the current source list.
*/
public int getPageCount() {
float nrOfPages = (float) getNrOfElements() / getPageSize();
return (int) ((nrOfPages > (int) nrOfPages || nrOfPages == 0.0) ? nrOfPages + 1 : nrOfPages);
}
/**
* Return if the current page is the first one.
*/
public boolean isFirstPage() {
return getPage() == 0;
}
/**
* Return if the current page is the last one.
*/
public boolean isLastPage() {
return getPage() == getPageCount() -1;
}
/**
* Switch to previous page.
* Will stay on first page if already on first page.
*/
public void previousPage() {
if (!isFirstPage()) {
this.page--;
}
}
/**
* Switch to next page.
* Will stay on last page if already on last page.
*/
public void nextPage() {
if (!isLastPage()) {
this.page++;
}
}
/**
* Return the total number of elements in the source list.
*/
public int getNrOfElements() {
return getSource().size();
}
/**
* Return the element index of the first element on the current page.
* Element numbering starts with 0.
*/
public int getFirstElementOnPage() {
return (getPageSize() * getPage());
}
/**
* Return the element index of the last element on the current page.
* Element numbering starts with 0.
*/
public int getLastElementOnPage() {
int endIndex = getPageSize() * (getPage() + 1);
int size = getNrOfElements();
return (endIndex > size ? size : endIndex) - 1;
}
/**
* Return a sub-list representing the current page.
*/
public List<E> getPageList() {
return getSource().subList(getFirstElementOnPage(), getLastElementOnPage() + 1);
}
/**
* Return the first page to which create a link around the current page.
*/
public int getFirstLinkedPage() {
return Math.max(0, getPage() - (getMaxLinkedPages() / 2));
}
/**
* Return the last page to which create a link around the current page.
*/
public int getLastLinkedPage() {
return Math.min(getFirstLinkedPage() + getMaxLinkedPages() - 1, getPageCount() - 1);
}
/**
* Resort the list if necessary, i.e. if the current {@code sort} instance
* isn't equal to the backed-up {@code sortUsed} instance.
* <p>Calls {@code doSort} to trigger actual sorting.
* @see #doSort
*/
public void resort() {
SortDefinition sort = getSort();
if (sort != null && !sort.equals(this.sortUsed)) {
this.sortUsed = copySortDefinition(sort);
doSort(getSource(), sort);
setPage(0);
}
}
/**
* Create a deep copy of the given sort definition,
* for use as state holder to compare a modified sort definition against.
* <p>Default implementation creates a MutableSortDefinition instance.
* Can be overridden in subclasses, in particular in case of custom
* extensions to the SortDefinition interface. Is allowed to return
* null, which means that no sort state will be held, triggering
* actual sorting for each {@code resort} call.
* @param sort the current SortDefinition object
* @return a deep copy of the SortDefinition object
* @see MutableSortDefinition#MutableSortDefinition(SortDefinition)
*/
protected SortDefinition copySortDefinition(SortDefinition sort) {
return new MutableSortDefinition(sort);
}
/**
* Actually perform sorting of the given source list, according to
* the given sort definition.
* <p>The default implementation uses Spring's PropertyComparator.
* Can be overridden in subclasses.
* @see PropertyComparator#sort(java.util.List, SortDefinition)
*/
protected void doSort(List<E> source, SortDefinition sort) {
PropertyComparator.sort(source, sort);
}
}