问题描述： 在使用JdbcTemplate进行数据查询时，如果数据库中的数据不存在那么就会出现以下异常信息
Exception in thread "main" org.springframework.dao.EmptyResultDataAccessException: Incorrect result size: expected 1, actual 0 at org.springframework.dao.support.DataAccessUtils.requiredSingleResult(DataAccessUtils.java:71) at org.springframework.jdbc.core.JdbcTemplate.queryForObject(JdbcTemplate.java:812)问提出现的原因 以下是spring中DataAccessUtils中出错的方法，当结果为null时就会抛出我们遇到的异常
public abstract class DataAccessUtils{ public static <T> T requiredSingleResult(Collection<T> results) throws IncorrectResultSizeDataAccessException { int size = results != null ? results.size() : 0; if (size == 0) { throw new EmptyResultDataAccessException(1); } else if (results.size() > 1) { throw new IncorrectResultSizeDataAccessException(1, size); } else { return results.iterator().next(); } } }解决方法 捕获这个异常
public User findUserByUserName(String username){ User user = null; String sql = "select * from tab_user where username = ?"; try { user =jdbcTemplate.queryForObject(sql, new BeanPropertyRowMapper<>(User.class), username); }catch (EmptyResultDataAccessException e){ return null; } return user; }