在上一篇文章中已經配置好struts2+spring+jpa+dwr，這篇我們來講下通用DAO設計。

設計思路：利用spring對dao層的支持，使用泛行方式對它進行一次包裝，此通用DAO只實現最基本的增刪改查功能，具體的特殊實現有它的子類實現

接口設計，在原來的工程中建立一個源代碼包，名稱為common，然后建立包結構，我的包結構如圖：

　
照片名稱：包結構
在dao目錄下創建BaseDao.java文件，此文件是一個接口，代碼如下：

/**
?* 基本的CRUD實現，使用方式：
?* 比如您有個DAO叫UserDao,那么UserDao的寫法如下：
?* UserDao extends BaseDao<Long, User>
?* UserDao的實現類的寫法是：
?* UserDaoImpl extends BaseJpaDaoSupport<Long, User> implements UserDao
?* @author HLIN
?*
?* @param <K>
?* @param <V>
?*/

public interface BaseDao<K extends Serializable, V> {
?　　void add(V entity) throws GenericDaoException;
?　　void delete(V entity) throws GenericDaoException;
?　　void delete(List<V> entities) throws GenericDaoException;
?　　void delete(K id) throws GenericDaoException;
?　　void update(V entity) throws GenericDaoException;
?　　V find(K id) throws GenericDaoException;
?　　V findSingle(String hql, Object... params) throws GenericDaoException;
?　　List<V> find(String ql, Object... params) throws GenericDaoException;
?　　List<V> findAll() throws GenericDaoException;
?　　List<V> pageQuery(PageBean pageBean,?String hql,?Object... params) throws GenericDaoException;

}

這個接口中，我們使用了泛型，第一個參數是表的主鍵，必須是對象類型的；第二個參數是實體類型，不首限制。

接下來就用hibernate和jpa兩種方式實現這個接口

hibernate實現，代碼如下：

public class BaseHibernateDaoSupport<K extends Serializable, V> extends
??HibernateDaoSupport implements BaseDao<K, V> {

?public void add(V entity) {
??getHibernateTemplate().save(entity);
?}

?public void delete(V entity) {
??getHibernateTemplate().delete(entity);
?}

?public void delete(List<V> entities) {
??getHibernateTemplate().deleteAll(entities);

?}
?
?public void delete(K id) {
??getHibernateTemplate().delete(find(id));
?}

?@SuppressWarnings("unchecked")
?public V find(K id) {
??return (V) getHibernateTemplate().get(getEntityType(), id);
?}
?
?public V findSingle(final String hql, final Object... params) {
??List<V> list = find(hql, params);
??if (list.size() > 0)
???return list.get(0);
??return null;
?}

?@SuppressWarnings("unchecked")
?public List<V> find(String hql, Object... params) {
??return getHibernateTemplate().find(hql, params);
?}

?public void update(V entity) {
??getHibernateTemplate().update(entity);
?}
?
?@SuppressWarnings("unchecked")
?public List<V> findAll() {
??return getHibernateTemplate().loadAll(getEntityType());
?}

?@SuppressWarnings("unchecked")
?public List<V> pageQuery(final PageBean pageBean, final String hql,
???final Object... params) {
??List<V> list = getHibernateTemplate().executeFind(
????new HibernateCallback() {
?????public Object doInHibernate(Session session)
???????throws HibernateException, SQLException {
??????Query query = session.createQuery(hql);
??????for (int i = 0; i < params.length; i++) {
???????query.setParameter(i, params[i]);
??????}
??????return query.setFirstResult(
????????(pageBean.getCurrentPage() - 1)
??????????* pageBean.getPageSize())
????????.setMaxResults(pageBean.getPageSize()).list();
?????}
????});
??pageBean.setTotalRecords(getRowCount(hql, params));
??return list;
?}

?private Integer getRowCount(String sql, Object... params) {
??sql = "select count(*) " + CommonUtil.removeSelect(CommonUtil.removeOrders(sql));
??return new Integer(findSingle(sql, params).toString());
?}

?@SuppressWarnings("unchecked")
?private Class<V> getEntityType() {
??return (Class<V>) ((ParameterizedType) getClass()
????.getGenericSuperclass()).getActualTypeArguments()[1];
?}

}

然后是JPA的實現，代碼如下：

public class BaseJpaDaoSupport<K extends Serializable, V> extends JpaDaoSupport implements BaseDao<K, V> {

?public void add(V entity)?{
??getJpaTemplate().persist(entity);
?}

?public void delete(V entity) {
??getJpaTemplate().remove(entity);
?}

?public void delete(List<V> entities) {
??for (V entity : entities)
???getJpaTemplate().remove(entity);
?}

?public void delete(K id) {
??getJpaTemplate().remove(find(id));
?}

?@SuppressWarnings("unchecked")
?public List<V> findAll() {
??String name = getEntityType().getName();
??return getJpaTemplate().find("from " + name.substring(name.lastIndexOf(".")+1));
?}

?public V find(K id) {
??return getJpaTemplate().find(getEntityType(), id);
?}

?@SuppressWarnings("unchecked")
?public List<V> find(String hql, Object... params) {
??return getJpaTemplate().find(hql, params);
?}
?
?@SuppressWarnings("unchecked")
?public V findSingle(final String hql, final Object... params) {
??return (V) getJpaTemplate().execute(new JpaCallback() {
???public Object doInJpa(EntityManager em)
?????throws PersistenceException {
????Query query = em.createQuery(hql);
????return query.getSingleResult();
???}
??});
?}

?@SuppressWarnings("unchecked")
?public List<V> pageQuery(final PageBean pageBean, final String hql, final Object... params) {
??return getJpaTemplate().executeFind(new JpaCallback() {
???public Object doInJpa(EntityManager em) throws PersistenceException {
????
????List<V> result = em.createQuery(hql).setFirstResult(
??????(pageBean.getCurrentPage() - 1)).setMaxResults(
????????pageBean.getPageSize()).getResultList();
????pageBean.setTotalRecords(getRowCount(hql, params));
????return result;
???}

??});
?}

?public void update(V entity) {
??getJpaTemplate().merge(entity);
?}
?
?private Integer getRowCount(String sql, Object... params) {
??sql = "select count(*) " + CommonUtil.removeSelect(CommonUtil.removeOrders(sql));
??return new Integer(findSingle(sql, params).toString());
?}

?@SuppressWarnings("unchecked")
?private Class<V> getEntityType() {
??return (Class<V>) ((ParameterizedType) getClass()
????.getGenericSuperclass()).getActualTypeArguments()[1];
?}

}

好了，大功告成，我們來寫個單元測試一下，這里的測試類使用的是spring的mock包，可以大大簡化我們的spring測試

首先寫一個測試基類，名稱為BaseTestCase,代碼如下：

public class BaseTestCase extends AbstractDependencyInjectionSpringContextTests {

?protected String[] getConfigLocations() {
??return new String[]{"classpath:spring-main.xml"};
?}

}

這里繼承的基類是AbstractDependencyInjectionSpringContextTests ，如果是在實際運行系統中測試，則需要繼承AbstractTransactionalSpringContextTests，代碼如下：

public class BaseTestCase extends AbstractDependencyInjectionSpringContextTests {

?protected String[] getConfigLocations() {
??return new String[]{"classpath:spring-main.xml"};
?}

}