Java视频学习笔记2------SSH------分页解决方案

对分页处理做成一个解决方案，适应不同的查询条件

抽象一个的管理器类，对分页的处理过程进行封装

package com.bjsxt.oa.manager.impl;    import java.util.List;    import org.hibernate.Query;  import org.springframework.orm.hibernate3.support.HibernateDaoSupport;    import com.bjsxt.oa.PagerModel;  import com.bjsxt.oa.manager.SystemException;    public class AbstractManager extends HibernateDaoSupport{        /**      * 根据Hql语句进行分页查询      * @param hql      * @param params      * @param offset      * @param pagesize      * @return      */      public PagerModel searchPaginated(String hql,Object[] params,int offset,int pagesize) {          //获取记录总数          String countHql = getCountQuery(hql);          Query query = getSession().createQuery(countHql);          if(params != null && params.length > 0){              for(int i=0; i<params.length; i++){                  query.setParameter(i, params[i]);              }          }          int total = ((Long)query.uniqueResult()).intValue();                    //获取结果集          query = getSession().createQuery(hql);          if(params != null && params.length > 0){              for(int i=0; i<params.length; i++){                  query.setParameter(i, params[i]);              }          }          query.setFirstResult(offset);          query.setMaxResults(pagesize);          List datas = query.list();                    //返回PagerModel          PagerModel pm = new PagerModel();          pm.setDatas(datas);          pm.setTotal(total);          return pm;      }            /**      * 根据HQL语句，获得查询总记录数的HQL语句      * 如：      * select ... from Organization o where o.parent is null      * 经过转换，可以得到：      * select count(*) from Organziation o where o.parent is null      * @param hql      * @return      */      private String getCountQuery(String hql) {          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【"+hql+"】");      }  }  

让业务逻辑类去继承AbstractManager

为了适应不同的情况，多设计几个接口方法：

/**  * 没有查询参数  * @param hql  * @param offset  * @param pagesize  * @return  */  public PagerModel searchPaginated(String hql,int offset,int pagesize) {      return searchPaginated(hql,null,offset,pagesize);  }  /**  * 有一个查询参数  * @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);  }  

原先的分页方法：

public PagerModel findOrgs(int parentId, int offset, int pagesize) {        String selectCountHql = "select count(*) from Orgnization o where o.parent is null";      if (parentId != 0) {          selectCountHql = "select count(*) from Orgnization o where o.parent.id = "                  + parentId;      }        int total = ((Long) getSession().createQuery(selectCountHql)              .uniqueResult()).intValue();        String selectHql = "select o from Orgnization o where o.parent is null";      if (parentId != 0) {          selectHql = "select o from Orgnization o where o.parent.id = "                  + parentId;      }        List datas = getSession().createQuery(selectHql).setFirstResult(offset)              .setMaxResults(pagesize).list();      PagerModel pm = new PagerModel();      pm.setDatas(datas);      pm.setTotal(total);        return pm;  }  

修改后的分页方法：

public PagerModel findOrgs(int parentId, int offset, int pagesize) {        String selectHql = "select o from Orgnization o where o.parent is null";      if (parentId != 0) {          selectHql = "select o from Orgnization o where o.parent.id = "                  + parentId;      }        return searchPaginated(selectHql, offset, pagesize);  }  

在开发过程中要形成一个不断地封装、抽象的意识。

我们还可以进一步的简化，把上面这两个参数去掉，而用其他的手段来传输这两个值来进一步封装。因为是在多线程的环境下运行，所以这两个属性不能写成普通的静态类型，可以用ThreadLocal来封装这两个参数。

定义SystemContext，在类中定义ThreadLocal。

package com.bjsxt.oa;    public class SystemContext {      private static ThreadLocal offset = new ThreadLocal();      private static ThreadLocal pagesize = new ThreadLocal();            public static void setOffset(int _offset){          offset.set(_offset);      }            public static int getOffset(){          Integer os = (Integer)offset.get();          if(os == null){              return 0;          }          return os;      }            public static void removeOffset(){          offset.remove();      }            public static void setPagesize(int _pagesize){          pagesize.set(_pagesize);      }            public static int getPagesize(){          Integer ps = (Integer)pagesize.get();          if(ps == null){              return Integer.MAX_VALUE;          }          return ps;      }            public static void removePagesize(){          pagesize.remove();      }  }  

定义一个过滤器调用set方法，在AbstractManager调用get方法

在过滤器里把offset，pagesize从客户端那取出来放到ThreadLocal中

package com.bjsxt.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.bjsxt.oa.SystemContext;    public class PagerFilter implements Filter {      public static final String PAGE_SIZE_NAME = "ps";        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中得值，防止内存溢出              SystemContext.removeOffset();              SystemContext.removePagesize();          }      }        private int getOffset(HttpServletRequest request) {          int offset = 0;          try {              offset = Integer.parseInt(request.getParameter("pager.offset"));          } catch (Exception ignore) {          }          return offset;      }        private int getPagesize(HttpServletRequest httpRequest) {          return 10;      }        public void init(FilterConfig arg0) throws ServletException {        }  } 

对AbstractManager方法进行修改扩充：

package com.bjsxt.oa.manager.impl;    import java.util.List;    import org.hibernate.Query;  import org.springframework.orm.hibernate3.support.HibernateDaoSupport;    import com.bjsxt.oa.PagerModel;  import com.bjsxt.oa.SystemContext;  import com.bjsxt.oa.manager.SystemException;    public class AbstractManager extends HibernateDaoSupport{      /**      * 只有hql语句      * @param hql      * @return      */      public PagerModel searchPaginated(String hql) {          return searchPaginated(hql,null,SystemContext.getOffset(),SystemContext.getPagesize());      }      /**      * 有一个查询参数      * @param hql      * @return      */      public PagerModel searchPaginated(String hql,Object obj) {          return searchPaginated(hql,new Object[]{obj},SystemContext.getOffset(),SystemContext.getPagesize());      }         /**      * 有多个查询参数      * @param hql      * @return      */      public PagerModel searchPaginated(String hql,Object[] params) {          return searchPaginated(hql,params,SystemContext.getOffset(),SystemContext.getPagesize());      }      /**      * 没有查询参数      * @param hql      * @param offset      * @param pagesize      * @return      */      public PagerModel searchPaginated(String hql,int offset,int pagesize) {          return searchPaginated(hql,null,offset,pagesize);      }      /**      * 有一个查询参数      * @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      * @param offset      * @param pagesize      * @return      */      public PagerModel searchPaginated(String hql,Object[] params,int offset,int pagesize) {          //获取记录总数          String countHql = getCountQuery(hql);          Query query = getSession().createQuery(countHql);          if(params != null && params.length > 0){              for(int i=0; i<params.length; i++){                  query.setParameter(i, params[i]);              }          }          int total = ((Long)query.uniqueResult()).intValue();                    //获取结果集          query = getSession().createQuery(hql);          if(params != null && params.length > 0){              for(int i=0; i<params.length; i++){                  query.setParameter(i, params[i]);              }          }          query.setFirstResult(offset);          query.setMaxResults(pagesize);          List datas = query.list();                    //返回PagerModel          PagerModel pm = new PagerModel();          pm.setDatas(datas);          pm.setTotal(total);          return pm;      }            /**      * 根据HQL语句，获得查询总记录数的HQL语句      * 如：      * select ... from Organization o where o.parent is null      * 经过转换，可以得到：      * select count(*) from Organziation o where o.parent is null      * @param hql      * @return      */      private String getCountQuery(String hql) {          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【"+hql+"】");      }  }

web.xml配置pagerFilter过滤器

<filter><filter-name>pagerFilter</filter-name><filter-class>com.bjsxt.oa.web.PagerFilter</filter-class></filter><filter-mapping><filter-name>pagerFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>