DAO层的代码介绍
DAO层的作用不多说了，大家都知道说下我的DAO层结构
BaseDao<T> 泛型类，模板类的基类
BaseDaoImpl<T> 泛型模板类
ResultHandle<T> 一个接口， 负责对结果集进行解析。
AbstractResultHandle<T> 抽象类，把公用的提取出来
BaseDao
public interface BaseDao<T> {/** * 查询单条记录的sql语句，如返回多条则只取第一条记录,没有记录返回null */public T executeQueryForEntity(String sql,Integer identity);/** * 一些不需要返回值的非query语句 */public void executeUpdate(String sql,Object... params);/** * 查询只返回一个整数值的sql，没有则返回0 */public Integer executeQueryForInteger(String sql,Object... params);/** * 返回插入数据的自增ID */public Integer executeInsertForInteger(String sql,Object... params);/** * 返回一个查询的列表,没有数据则返回空的list */public List<T> executeQueryForListEntity(String sql,Object... params);}
BaseDaoImpl
public class BaseDaoImpl<T> implements BaseDao<T>{//从filter中获得连接，最后又filter进行释放，见BlogFilterConnection conn = BlogFilter.getConnection();ResultHandle<T> handle;//通过构造方法传入相应的结果集解析实现public BaseDaoImpl(ResultHandle<T> handle){this.handle=handle;}//第一个参数为sql语句，第二个为参数数组，和sql中?位置对应@Overridepublic void executeUpdate(String sql,Object... params){try {PreparedStatement pstat = conn.prepareStatement(sql);for(int i=1;i<=params.length;i++)pstat.setObject(i, params);pstat.executeUpdate();} catch (SQLException e) {throw new RuntimeException(e);}}@Overridepublic T executeQueryForEntity(String sql, Integer identity) {try {PreparedStatement pstat = conn.prepareStatement(sql);pstat.setObject(1,identity);ResultSet res = pstat.executeQuery();//调用恰当的方法，用解析器进行解析return handle.getBean(res);} catch (SQLException e) {throw new RuntimeException(e);} }@Overridepublic Integer executeQueryForInteger(String sql, Object... params) {try {PreparedStatement pstat = conn.prepareStatement(sql);for(int i=1;i<=params.length;i++)pstat.setObject(i, params);ResultSet res = pstat.executeQuery();//如果查询的结果集为空，则返回0。貌似没有为空的if(!res.next()) return 0; return res.getInt(1);} catch (SQLException e) {throw new RuntimeException(e);}}@Overridepublic Integer executeInsertForInteger(String sql, Object... params) {try {PreparedStatement pstat = conn.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);for(int i=1;i<=params.length;i++)pstat.setObject(i, params);pstat.executeUpdate();//取得插入数据后包含，主键值的结果集ResultSet res = pstat.getGeneratedKeys();res.next();return res.getInt(1);} catch (SQLException e) {throw new RuntimeException(e);}}@Overridepublic List<T> executeQueryForListEntity(String sql, Object... params) {try {PreparedStatement pstat = conn.prepareStatement(sql,ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);for(int i=1;i<=params.length;i++)pstat.setObject(i, params);ResultSet res = pstat.executeQuery();return handle.getBeanList(res);} catch (SQLException e) {throw new RuntimeException(e);}}/** * 后增加的，多处用到，所有提起到了模板类里面 * @param sql一个sql语句，不含参数。如：select count(*) from table; 用于取得可计算的结果总数 * @param pageSize每页的现实数 * @return 最少返回1 */public Integer getMaxPageNum(String sql,Integer pageSize) {Integer total = executeQueryForInteger(sql, new Object[]{});if(total==0) return 1;//计算一共有多少页int maxNum = total/pageSize;//不足一页，则返回1if(total%pageSize!=0) maxNum+=1;return maxNum;}}
具体使用以评论表为例子
CommentDao
public interface CommentDao {public void addComment(Comment comment);public void deleteComment(Integer commentId);public List<Comment> getListComment(Integer articleId);public Integer getNumOfCommentForArticle(Integer articleId);public List<Comment> getLaterCommentList(Integer size);}CommentDaoImpl
public class CommentDaoImpl extends BaseDaoImpl<Comment> implements CommentDao {public CommentDaoImpl( ) {super(new CommentResultHandle());}@Overridepublic void addComment(Comment comment) {String sql = "insert into comment(comment_body,comment_date,comment_name,comment_image,article_id) values(?,?,?,?,?)";Object []params = {comment.getCommentBody(),comment.getCommentDate(),comment.getCommentName(),comment.getCommentImage(),comment.getArticleId()};Integer id = super.executeInsertForInteger(sql, params);comment.setCommentId(id);}@Overridepublic void deleteComment(Integer commentId) {String sql = "delete from comment where comment_id = ?";super.executeUpdate(sql, commentId);}@Overridepublic List<Comment> getListComment(Integer articleId) {String sql = "select * from comment where article_id = ?";return super.executeQueryForListEntity(sql, articleId);}@Overridepublic Integer getNumOfCommentForArticle(Integer articleId) {String sql = "select count(*) from comment where article_id = ?";return super.executeQueryForInteger(sql, articleId);}@Overridepublic List<Comment> getLaterCommentList(Integer size) {String sql = "select * from comment order by comment_date desc limit ?";return super.executeQueryForListEntity(sql, size);}} 下面贴出结果集解析的代码
ResultHandle<T>
public interface ResultHandle<T> {public T getBean(ResultSet res);public List<T> getBeanList(ResultSet res);}
AbstractResultHandle
public abstract class AbstractResultHandle<T> implements ResultHandle<T> {/** * 为了提高代码的再利用所以，把getBeanList方法提取到了这个抽象类中 */@Overridepublic List<T> getBeanList(ResultSet res) {try {//如果不存在任何数据则返回空的listif(!res.first()){return Collections.emptyList();}//将当前游标移动到第一行之上res.previous();} catch (SQLException e) {throw new RuntimeException(e);}List<T> list = new ArrayList<T>();//将每行数据封装成实体对象并添加到list，c为null时表示所给全部记录封装完毕T c = getBean(res);while(c!=null){list.add(c);c = getBean(res);}return list;}} CommentResultHandle
public class CommentResultHandle extends AbstractResultHandle<Comment> {@Overridepublic Comment getBean(ResultSet res) {try {if(res.next()){Comment c = new Comment();c.setArticleId(res.getInt("article_id"));c.setCommentBody(res.getString("comment_body"));c.setCommentDate(new Date(res.getTimestamp("comment_date").getTime()));c.setCommentId(res.getInt("comment_id"));c.setCommentImage(res.getString("comment_image"));c.setCommentName(res.getString("comment_name"));return c;}else return null;} catch (SQLException e) {throw new RuntimeException(e);}}} 虽然比价简陋，都还能凑合着用。一旦表的数量太多，那恐怕就成负担了。
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