jdbcTemplate.queryForObject 方法注意

正确方法：

String sql = "select ID from Structures(nolock) where id=?";
Integer ret = jdbcTemplate.queryForObject(sql, Integer.class, new Object[]{id});

错误方法：

String sql = "select ID from Structures(nolock) where id=?";
int ret = jdbcTemplate.queryForObject(sql, int.class, new Object[]{id});

String sql = "select * from Structures(nolock) where id=?";
Structure ret = jdbcTemplate.queryForObject(sql, Structure.class, new Object[]{id});

源代码：

public <T> T queryForObject(String sql, Class<T> requiredType, Object... args) throws DataAccessException {
  return queryForObject(sql, args, getSingleColumnRowMapper(requiredType));
}

错误分析：queryForObject此重装第2个参数Class<T> requiredType只能是基本数据类型的封装类，如Integer、String

正确方法：

String sql = "select * from Structures(nolock) where id=?";
jdbcTemplate.queryForObject(sql,new Object[]{id},new BeanPropertyRowMapper<Structure>(Structure.class));

源代码：

public <T> T queryForObject(String sql, Object[] args, RowMapper<T> rowMapper) throws DataAccessException {
  List<T> results = query(sql, args, new RowMapperResultSetExtractor<T>(rowMapper, 1));
  return DataAccessUtils.requiredSingleResult(results);
}

或者继承queryForObject此实现第3个参数接口RowMapper<T> rowMapper的类，例如：

public class UserInfo implements RowMapper<userinfo>, Serializable {
        private Integer id; 
  private String name;
  @Override
      public UserInfo mapRow(ResultSet rs, int rowNum) throws SQLException {
          UserInfo userInfo = new UserInfo();
          userInfo.setId(rs.getInt(id));
          userInfo.setUname(rs.getString(uname));
          userInfo.setUnumber(rs.getInt(unumber));
          userInfo.setuRegisterTime(rs.getDate(uregister_time));
          return userInfo;
      }
}

简单方法不在类上实现接口：

<span style="white-space:pre">    </span>String sql = "select GoodComments,BadComments,UseCount from Structures(nolock) where id=?";
    return jdbcTemplate.queryForObject(sql, new RowMapper<Structure>(){
      @Override
      public Structure mapRow(ResultSet rs, int rowNum) throws SQLException{
        Structure structure = new Structure();
        structure.setGoodComments(rs.getInt("GoodComments"));
        structure.setBadComments(rs.getInt("BadComments"));
        structure.setUseCount(rs.getInt("UseCount"));
        return structure;
      }
    }, id);