首先是接口 DAO

package cn.itcast.service.base;

import java.io.Serializable;
import java.util.LinkedHashMap;

import cn.itcast.bean.QueryResult;

public interface DAO<T> {
 /**
  * 获取记录总数
  * @param entityClass 实体类
  * @return
  */
 public long getCount();
 /**
  * 清除一级缓存的数据
  */
 public void clear();
 /**
  * 保存实体
  * @param entity 实体id
  */
 public void save(T entity);
 /**
  * 更新实体
  * @param entity 实体id
  */
 public void update(T entity);
 /**
  * 删除实体
  * @param entityClass 实体类
  * @param entityids 实体id数组
  */
 public void delete(Serializable ... entityids);
 /**
  * 获取实体
  * @param <T>
  * @param entityClass 实体类
  * @param entityId 实体id
  * @return
  */
 public T find(Serializable entityId);
 /**
  * 获取分页数据
  * @param <T>
  * @param entityClass 实体类
  * @param firstindex 开始索引
  * @param maxresult 需要获取的记录数
  * @return
  */
 public QueryResult<T> getScrollData(int firstindex, int maxresult, String wherejpql, Object[] queryParams,LinkedHashMap<String, String> orderby);
 
 public QueryResult<T> getScrollData(int firstindex, int maxresult, String wherejpql, Object[] queryParams);
 
 public QueryResult<T> getScrollData(int firstindex, int maxresult, LinkedHashMap<String, String> orderby);
 
 public QueryResult<T> getScrollData(int firstindex, int maxresult);
 
 public QueryResult<T> getScrollData();
}

然后是实现此接口的抽象类

DaoSupport

package cn.itcast.service.base;

import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.io.Serializable;
import java.lang.reflect.Method;
import java.util.LinkedHashMap;

import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

import cn.itcast.bean.QueryResult;
import cn.itcast.utils.GenericsUtils;

@SuppressWarnings("unchecked")
@Transactional
public abstract class DaoSupport<T> implements DAO<T>{
 protected Class<T> entityClass = GenericsUtils.getSuperClassGenricType(this.getClass());
 @PersistenceContext protected EntityManager em;
 
 public void clear(){
  em.clear();
 }

public void delete(Serializable ... entityids) {
  for(Object id : entityids){
   em.remove(em.getReference(this.entityClass, id));
  }
 }
 
 @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
 public T find(Serializable entityId) {
  if(entityId==null) throw new RuntimeException(this.entityClass.getName()+ ":传入的实体id不能为空");
  return em.find(this.entityClass, entityId);
 }

public void save(T entity) {
  em.persist(entity);
 }
 
 @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
 public long getCount() {
  return (Long)em.createQuery("select count("+ getCountField(this.entityClass) +") from "+ getEntityName(this.entityClass)+ " o").getSingleResult();
 }
 
 public void update(T entity) {
  em.merge(entity);
 }
 
 @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
 public QueryResult<T> getScrollData(int firstindex, int maxresult, LinkedHashMap<String, String> orderby) {
  return getScrollData(firstindex,maxresult,null,null,orderby);
 }
 
 @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
 public QueryResult<T> getScrollData(int firstindex, int maxresult, String wherejpql, Object[] queryParams) {
  return getScrollData(firstindex,maxresult,wherejpql,queryParams,null);
 }
 
 @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
 public QueryResult<T> getScrollData(int firstindex, int maxresult) {
  return getScrollData(firstindex,maxresult,null,null,null);
 }
 
 @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
 public QueryResult<T> getScrollData() {
  return getScrollData(-1, -1);
 }

@Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED)
 public QueryResult<T> getScrollData(int firstindex, int maxresult
   , String wherejpql, Object[] queryParams,LinkedHashMap<String, String> orderby) {
  QueryResult qr = new QueryResult<T>();
  String entityname = getEntityName(this.entityClass);
  Query query = em.createQuery("select o from "+ entityname+ " o "+(wherejpql==null || "".equals(wherejpql.trim())? "": "where "+ wherejpql)+ buildOrderby(orderby));
  setQueryParams(query, queryParams);
  if(firstindex!=-1 && maxresult!=-1) query.setFirstResult(firstindex).setMaxResults(maxresult);
  qr.setResultlist(query.getResultList());
  query = em.createQuery("select count("+ getCountField(this.entityClass)+ ") from "+ entityname+ " o "+(wherejpql==null || "".equals(wherejpql.trim())? "": "where "+ wherejpql));
  setQueryParams(query, queryParams);
  qr.setTotalrecord((Long)query.getSingleResult());
  return qr;
 }
 
 protected static void setQueryParams(Query query, Object[] queryParams){
  if(queryParams!=null && queryParams.length>0){
   for(int i=0; i<queryParams.length; i++){
    query.setParameter(i+1, queryParams[i]);
   }
  }
 }
 /**
  * 组装order by语句
  * @param orderby
  * @return
  */
 protected static String buildOrderby(LinkedHashMap<String, String> orderby){
  StringBuffer orderbyql = new StringBuffer("");
  if(orderby!=null && orderby.size()>0){
   orderbyql.append(" order by ");
   for(String key : orderby.keySet()){
    orderbyql.append("o.").append(key).append(" ").append(orderby.get(key)).append(",");
   }
   orderbyql.deleteCharAt(orderbyql.length()-1);
  }
  return orderbyql.toString();
 }
 /**
  * 获取实体的名称
  * @param <E>
  * @param clazz 实体类
  * @return
  */
 protected static <E> String getEntityName(Class<E> clazz){
  String entityname = clazz.getSimpleName();
  Entity entity = clazz.getAnnotation(Entity.class);
  if(entity.name()!=null && !"".equals(entity.name())){
   entityname = entity.name();
  }
  return entityname;
 }
 /**
  * 获取统计属性,该方法是为了解决hibernate解析联合主键select count(o) from Xxx o语句BUG而增加,hibernate对此jpql解析后的sql为select count(field1,field2,...),显示使用count()统计多个字段是错误的
  * @param <E>
  * @param clazz
  * @return
  */
 protected static <E> String getCountField(Class<E> clazz){
  String out = "o";
  try {
   PropertyDescriptor[] propertyDescriptors = Introspector.getBeanInfo(clazz).getPropertyDescriptors();
   for(PropertyDescriptor propertydesc : propertyDescriptors){
    Method method = propertydesc.getReadMethod();
    if(method!=null && method.isAnnotationPresent(EmbeddedId.class)){     
     PropertyDescriptor[] ps = Introspector.getBeanInfo(propertydesc.getPropertyType()).getPropertyDescriptors();
     out = "o."+ propertydesc.getName()+ "." + (!ps[1].getName().equals("class")? ps[1].getName(): ps[0].getName());
     break;
    }
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
        return out;
 }
}