Pager-taglib在项目中的使用
在上篇文章Pager-taglib分页 对其有了一个基本的了解,接下来我们将会对pager-taglib如何在项目中使用进行一个比较详细的说明.
1建立LocalThread类,对分页的常数进行封装
代码如下
package com.tgb.oa;
/**
*
* 采用ThreadLocal来存储分页变量.
* @author jnqqls
* @group TGB
* @version 1.0
* @comments
*/
public class SystemContext {
private static ThreadLocal offset = new ThreadLocal();
private static ThreadLocal pagesize = new ThreadLocal();
/**
* 从线程中获取offset字段
* @return
*/
public static int getOffset(){
Integer os = (Integer)offset.get();
if(os == null){
return 0;
}
return os;
}
public static void setOffset(int offsetvalue){
offset.set(offsetvalue);
}
public static void removeOffset(){
offset.remove();
}
public static int getPagesize(){
Integer ps = (Integer)pagesize.get();
if(ps == null){
return Integer.MAX_VALUE;
}
return ps;
}
public static void setPagesize(int pagesizevalue){
pagesize.set(pagesizevalue);
}
public static void removePagesize(){
pagesize.remove();
}
}
2建立PagerFilter过滤器,将参数读取到ThreadLocal中.
代码如下:
package com.tgb.oa.web;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import com.tgb.oa.SystemContext;
/**
*
* @oa_02 过滤器,获取相关分页数据.
* @author jnqqls
* @group TGB
* @version 1.0
* @comments
*/
public class PagerFilter implements Filter {
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest httpRequest = (HttpServletRequest)request;
SystemContext.setOffset(getOffset(httpRequest));
SystemContext.setPagesize(getPagesize(httpRequest));
try{
chain.doFilter(request, response);
}finally{
//清空ThreadLocal中的值,避免类的溢出.
SystemContext.removeOffset();
SystemContext.removePagesize();
}
}
protected int getOffset(HttpServletRequest request){
int offset = 0;
try {
offset = Integer.parseInt(request.getParameter("pager.offset"));
} catch (NumberFormatException ignore) {
}
return offset;
}
protected int getPagesize(HttpServletRequest request){
return 10;
}
public void init(FilterConfig arg0) throws ServletException {
}
}
3配置filter在WEB.XML文件中
代码如下:
<!-- 定义分页Filter -->
<filter>
<filter-name>PagerFilter</filter-name>
<filter-class>com.tgb.oa.web.PagerFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>PagerFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
4建立抽象类,将分页功能抽象成一个方案,可以在更多的场合下进行运用.
代码如下:
package com.tgb.oa.manager.impl;
import java.util.List;
import org.hibernate.Query;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;
import com.tgb.oa.PagerModel;
import com.tgb.oa.SystemContext;
import com.tgb.oa.manager.SystemException;
/**
*
* 抽象分页查询.
* @author jnqqls
* @group TGB
* @version 1.0
* @comments
*/
public class AbstractManager extends HibernateDaoSupport {
public PagerModel searchPaginated(String hql){
return searchPaginated(hql,null,SystemContext.getOffset(),SystemContext.getPagesize());
}
public PagerModel searchPaginated(String hql,Object param){
return searchPaginated(hql,new Object[]{param},SystemContext.getOffset(),SystemContext.getPagesize());
}
public PagerModel searchPaginated(String hql,Object[] params){
return searchPaginated(hql,params,SystemContext.getOffset(),SystemContext.getPagesize());
}
/**
* 没有参数
* @param hql
* @param offset
* @param pagesize
* @return
*/
public PagerModel searchPaginated(String hql,int offset,int pagesize){
return searchPaginated(hql,null,offset,pagesize);
}
/**
* 只有一个参数
* @param hql
* @param obj
* @param offset
* @param pagesize
* @return
*/
public PagerModel searchPaginated(String hql,Object obj,int offset,int pagesize){
return searchPaginated(hql,new Object[]{obj},offset,pagesize);
}
/**
* 根据hql语句进行分页查询
* @param hql
* @param params HQL语句带的多个参数值.
* @param offset 从第几条记录开始查询
* @param pagesize 总共要显示的页数.
* @return
*/
public PagerModel searchPaginated(String hql,Object[] params,int offset,int pagesize){
//第一步:获取总记录数.
//获取总数的查询语句
String countHql=getCountQuery(hql);
//创建查询对象.
Query query =getSession().createQuery(countHql);
//通过循环将参数设置到语句中.
if(params != null && params.length>0){
for(int i=0;i<params.length;i++){
query.setParameter(i, params[i]);
}
}
//获取总的记录数
int total = ((Long)query.uniqueResult()).intValue();
//获取当前的结果集
query = getSession().createQuery(hql);
if(params != null && params.length>0){
for(int i=0;i<params.length;i++){
query.setParameter(i, params[i]);
}
}
//设置参数
query.setFirstResult(offset);
query.setMaxResults(pagesize);
//获取结果集.
List datas=query.list();
//创建PagerModel对象.
PagerModel pm = new PagerModel();
pm.setDatas(datas);
pm.setTotal(total);
return pm;
}
/**
* 根据HQL语句,获得查找总记录数的HQL语句.
* @param hql
* @return
*/
private String getCountQuery(String hql) {
//根据from字截取查询语句.
int index = hql.indexOf("from");
if(index != -1){
return "select count(*) " + hql.substring(index);
}
throw new SystemException("无效的HQL查询语句！");
}
}
5实现抽象类,完成方法的调用.
代码如下:
package com.tgb.oa.manager.impl;
import java.util.List;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;
import com.tgb.oa.PagerModel;
import com.tgb.oa.manager.OrgManager;
import com.tgb.oa.model.Orgnization;
/**
*
* @ 实现组织机构管理接口
* @author jnqqls
* @group TGB
* @version 1.0
* @comments
*/
public class OrgManagerImpl extends AbstractManager implements OrgManager {
@Override
public PagerModel findOrgs(int parentId) {
//如果parentId＝0，则查找顶级机构列表
if(parentId == 0){
return searchPaginated("from Orgnization o where o.parent is null");
}
return searchPaginated("from Orgnization o where o.parent.id = ?", parentId);
}
}
剩下的就是相关的 Action进行调用,配置jsp页面.以上便是pager-taglib在项目中后台的相关使用.
总结:pager-taglib是分页的一个好工具，经过简单的配置可以轻松实现分页功能,我们所需要学习的是它本身所具有封装思想.