Springframework中的JdbcTemplate.query()详情分析

Spring框架集成了JDBC的功能。

Spring JdbcDaoSupport 执行SQL的详情――

return int: getJdbcTemplate().queryForInt(sql)  ： select count(*)...
return List:getJdbcTemplate().query(sql, rowMapper)  ： select ... from ...
return null:getJdbcTemplate().update(sql)   ： insert into ... values or delete from ... 
return null:getJdbcTemplate().update(sql, objects, types)  ： insert into ... values 
return List:getJdbcTemplate().query(sql, new Object[] { assetId }, new int[] { Types.INTEGER }, rowMapper)    ：select * from ... where id=

Object[] objects = new Object[]{user.getId(),user.getName(),user.getPassword()...};
int[] types = new int[]{Type.VARCHAR,Type.VARCHAR,Type.VARCHAR,...}

RowMapper对象：
RowMapper的 mapRow() 方法是留给我们去组装实体类用的,返回是这种类的集合List。

Public List<User> getUsers() {
        String sql = "select * from User";
        return getJdbcTemplate().query(sql,new ItemRowMapper());
}

protected class ItemRowMapper implements RowMapper { //这个类也可以定义在方法里，如下。

        RowMapper rowMapper = new RowMapper(){}
        public Object mapRow(ResultSet rs, int rowNum) throws SQLException { 
                  Item item = new Item(); 
                  item.setId(rs.getInt("id")); 
                  item.setUserId(rs.getInt("user_id")); 
                  item.setName(rs.getString("name")); 
                  item.setEmail(rs.getString("email")); 
                  return item; 
        } 
}

想象 getJdbcTemplate().query()方法 和 RowMapper类。

public List query(String sql, RowMapper rowMapper){
        int num = 0;
        List<Object> list = null;
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try{
              conn = getConn();
              pstmt = conn.prepareStatement(sql);
              rs = pstmt.executeQuery();
              num = 0;
              while(rs.next()){num++};
              list = rowMapper.execute(rs, num);
        }catch(Exception e){
  
        }finall{
              rs.close();
              pstmt.close();
              conn.close();
        }
        return list;
}
abstract Class RowMapper(){
        List<Object> list = null;
        public List execute(ResultSet rs, int rowNum){ //rowNum没用到
             while(rs.next){
                   list.add(mapRow(rs, rowNum));
              }
              return list;
        }
    public Object mapRow(ResultSet rs, int RowNum);
}