DAO层代码优化

DAO层代码重复的很多，可以使用模板方法进行优化

1. 首先再目录下再定义一个包common

2. 再在报下新建接口JDBCCallback

public interface JDBCallback<T> {

   T reToObject(ResultSet rs) throws SQLException;
   void setParams(PreparedStatement stmt) throws SQLException;  //设置参数

}

3. 在包下新建一个抽象类JDBCAbstractCallBack

public abstract class JDBCAbstractCallBack<T> implements JDBCCallBack<T> {

   @override
   public T reToObject(ResultSet rs){
       return null;
   };
   public setParams(PreparedStatement stmt){
         return null;
   };
}

4. 再在包下再新建一个类JDBCTemplate1<T> (采用泛型)

public class JDBCTemplate<T> {

   public List<T> query(String sql, JDBCCallback<T> jdbcCallback) {
       Connection conn = null;
       PreparedStatement stmt = null;
       ResultSet rs = null;
       List<T> data = new ArrayList<T>();
       try {
           conn = DBUtil.getConnection();
           stmt = conn.preparedStatement(sql);

           rs = stmt.excuteQuery();
                       while(rs.next()) {
                           T object = jdbcCallback.rsToObject(rs);
                            data.add(object);
                       }

       } catch (SQLException e) {
           e.printStackTrace();
       } finally {
           DBUtil.close(rs, stmt, conn);
       }

       return data;
   }
} 

5. 在DAO中调用

JDBCTemplate<Book> jdbcTemlate = new JDBCTemplate<Book>();
jdbcTemlate.query(sql, new JDBCAbstractCallBack<Book>(){
         @override
         public Book rsToObject(ResultSet rs) throws SQLException {
              Book book = new Book();
              book.setxxxx(rs.getXXX(xxx));
              return book;
         }
  }  );