StandardDAOImpl

package th.athichitsakul.dao.impl;

import java.lang.reflect.ParameterizedType;
import java.util.List;

import th.athichitsakul.dao.DAO;
import th.athichitsakul.dao.StandardDAO;

public abstract class StandardDAOImpl<T> implements StandardDAO<T>{
    Class<T> objectClass;
    protected DAO DAO = null;
    public StandardDAOImpl(String puID)  {
        this.DAO = new DAO(puID);
        objectClass = (Class<T>)((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }
    public void save(T object)throws Exception{
        try{
            DAO.begin();
            DAO.save(object);
        }catch(Exception e){

            if (DAO.getTransaction().isActive()) {
                DAO.getTransaction().rollback();
            }
            throw e;
        }finally{
            DAO.close();
        }
    }
    public void remove(Object primaryKey)throws Exception{
        try{
            DAO.begin();
            Object object = DAO.getEntityManager().find(objectClass, primaryKey);
            if(object==null) throw new NullPointerException("Removing Object Not Found");
            DAO.getEntityManager().remove(object);
        }catch(Exception e){
            throw e;
        }finally{
            DAO.close();
        }
    }
    public T find(Object primaryKey) throws Exception{
        T queryResult = null;
        try{
            DAO.begin();
            queryResult = DAO.getEntityManager().find(objectClass, primaryKey);
        }catch(Exception e){
            throw e;
        }finally{
            DAO.close();
        }
        return queryResult;
    }
    public List<T> list() throws Exception{
        List<T> queryResult = null;
        try{
            DAO.begin();
            queryResult = DAO.getEntityManager().createQuery("FROM ".concat(objectClass.getName() )).getResultList();
        }catch(Exception e){
            throw e;
        }finally{
            DAO.close();
        }
        return queryResult;
    }
}