用泛型与反射技术封装分页功能(示例代码)

DAO.java
public interface DAO {
/**
* 1.获取所要显示的分页数据(一般以list形式来存放)
* 2.获取记录的总数(计算总页数)
* 3.需要定义一个返回类型，获取两个参数
* @param <T>
* @param entityClass 实体类
* @param firstindex 开始索引
* @param maxresult 需要获取记录数
* @return
*/
public <T> QueryResult<T> getScrollData(Class<T> entityClass, int firstindex, int maxresult);}

QueryResult.java(需要定义一个返回类型，获取两个参数)
package com.itcast.bean;
import java.util.List;
public class QueryResult<T> {
private List<T> resultlist;
private long totalrecord;
public List<T> getResultlist(){
return resultlist;
}
public void setResultlist(List<T> resultlist) {
this.resultlist = resultlist;
}
public long getTotalrecord() {
return totalrecord;
}
public void setTotalrecord(long totalrecord) {
this.totalrecord = totalrecord;
}
}

DaoSupport.java
import com.itcast.bean.QueryResult;
public abstract class DaoSupport implements DAO {
@SuppressWarnings("unchecked")
@Override
@Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
public <T> QueryResult<T> getScrollData(Class<T> entityClass, int firstindex, int maxresult) {
//创建查询对象
QueryResult qr = new QueryResult<T>();
//获取实体名称
String entityname = getEntityName(entityClass);
Query query = em.createQuery("select o from "+entityname+" o");
query.setFirstResult(firstindex).setMaxResults(maxresult);
qr.setResultlist(query.getResultList());
query = em.createQuery("select count(o) from "+entityname+" o");
qr.setTotalrecord((Long)query.getSingleResult());
return qr;
}

/**
* 获取实体名称
* @param <T>
* @param entityClass实体类
* @return
*/
protected <T> String getEntityName(Class<T> entityClass){
String entityname = entityClass.getSimpleName();
Entity entity = entityClass.getAnnotation(Entity.class);
if(entity.name()!=null && !"".equals(entity.name())){
entityname = entity.name();
}
return entityname;
}
}