Spring 框架 执行SQL getJdbcTemplate().query update 用法

Spring JdbcDaoSupport 执行SQL

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 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 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