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JdbcTemplate中queryForObject的EmptyResultDataAccessException问题

在使用Spring提供的JdbcTemplate中名为queryForObject API进行数据库查询时有时会抛出如下异常提示息,org.springframework.dao.EmptyResultDataAccessException: Incorrect result size: expected 1, actual 0 或者 org.springframework.dao.IncorrectResultSizeDataAccessException: Incorrect result size: expected 1, actual 2 

在解决这些异常之前,我们首先来看看queryForObject API的源代码,假设我们调用的是queryForObjec(String sql, Class requiredType)。 

JdbcTemplate.class 

public <T> T queryForObject(String sql, Class<T> requiredType) 		throws DataAccessException {return queryForObject(sql, getSingleColumnRowMapper(requiredType));}public <T> T queryForObject(String sql, RowMapper<T> rowMapper) 		throws DataAccessException {    List<T> results = query(sql, rowMapper);    return DataAccessUtils.requiredSingleResult(results);}public <T> List<T> query(String sql, RowMapper<T> rowMapper) 		throws DataAccessException {    return query(sql, new RowMapperResultSetExtractor<T>(rowMapper));}public <T> T query(final String sql, final ResultSetExtractor<T> rse) 		throws DataAccessException {	Assert.notNull(sql, "SQL must not be null");	Assert.notNull(rse, "ResultSetExtractor must not be null");	if (logger.isDebugEnabled()) {		logger.debug("Executing SQL query [" + sql + "]");	}	class QueryStatementCallback implements StatementCallback<T>, SqlProvider {		public T doInStatement(Statement stmt) throws SQLException {			ResultSet rs = null;			try {				rs = stmt.executeQuery(sql);				ResultSet rsToUse = rs;				if (nativeJdbcExtractor != null) {					rsToUse = nativeJdbcExtractor.getNativeResultSet(rs);				}				return rse.extractData(rsToUse);			}			finally {				JdbcUtils.closeResultSet(rs);			}		}		public String getSql() {			return sql;		}	}	return execute(new QueryStatementCallback());}

  DataAccessUtils.class 

public static <T> T requiredSingleResult(Collection<T> results)         throws IncorrectResultSizeDataAccessException {    int size = (results != null ? results.size() : 0);    if (size == 0) {        throw new EmptyResultDataAccessException(1);    }    if (results.size() > 1) {        throw new IncorrectResultSizeDataAccessException(1, size);    }    return results.iterator().next();}

通过阅读源代码,可以很清楚看到在DataAccessUtils.class中requiredSingleResult方法中,当结果集合的size为0或者大于1时,就会抛出以上两个异常。 

为了避免出现以上的异常,最好还是使用queryForList 或者query来进行查询,这样返回的结果为List,即使返回的结果集合的size为0,即Zero Row,也不会抛出异常。如果size不为0,即可以使用get(0)取得第一个查询对象。 

JdbcTemplate中queryForObject的EmptyResultDataAccessException问题