简单的Dao层的模板写法

Posted 2021-12-24 huangpeideng

public class CategoryDAO 

    public int getTotal() 
        int total = 0;
        try (Connection c = DBUtil.getConnection(); Statement s = c.createStatement()) 

            String sql = "select count(*) from Category";

            ResultSet rs = s.executeQuery(sql);
            while (rs.next()) 
                total = rs.getInt(1);
            
         catch (SQLException e) 

            e.printStackTrace();
        
        return total;
    

    public void add(Category bean) 

        String sql = "insert into category values(null,?)";
        try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql)) 

            ps.setString(1, bean.getName());

            ps.execute();

            ResultSet rs = ps.getGeneratedKeys();
            if (rs.next()) 
                int id = rs.getInt(1);
                bean.setId(id);
            
         catch (SQLException e) 

            e.printStackTrace();
        
    

    public void update(Category bean) 

        String sql = "update category set name= ? where id = ?";
        try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql)) 

            ps.setString(1, bean.getName());
            ps.setInt(2, bean.getId());

            ps.execute();

         catch (SQLException e) 

            e.printStackTrace();
        

    

    public void delete(int id) 

        try (Connection c = DBUtil.getConnection(); Statement s = c.createStatement()) 

            String sql = "delete from Category where id = " + id;

            s.execute(sql);

         catch (SQLException e) 

            e.printStackTrace();
        
    

    public Category get(int id) 
        Category bean = null;

        try (Connection c = DBUtil.getConnection(); Statement s = c.createStatement()) 

            String sql = "select * from Category where id = " + id;

            ResultSet rs = s.executeQuery(sql);

            if (rs.next()) 
                bean = new Category();
                String name = rs.getString(2);
                bean.setName(name);
                bean.setId(id);
            

         catch (SQLException e) 

            e.printStackTrace();
        
        return bean;
    

    public List<Category> list() 
        return list(0, Short.MAX_VALUE);
    

    public List<Category> list(int start, int count) 
        List<Category> beans = new ArrayList<Category>();

        String sql = "select * from Category order by id desc limit ?,? ";

        try (Connection c = DBUtil.getConnection(); PreparedStatement ps = c.prepareStatement(sql)) 

            ps.setInt(1, start);
            ps.setInt(2, count);

            ResultSet rs = ps.executeQuery();

            while (rs.next()) 
                Category bean = new Category();
                int id = rs.getInt(1);
                String name = rs.getString(2);
                bean.setId(id);
                bean.setName(name);
                beans.add(bean);
            
         catch (SQLException e) 
            e.printStackTrace();
        
        return beans;