Java.sql.ResultSet ResultSetMetaData.getColumnCount() out of range

 nested exception is java.sql.SQLException:Column index out of range.;caused: Column index out of range.;

Java.sql.ResultSet
       ResultSetmetaData 对象
               在JDBC返回了信息的情况下，metaData.getColumnName(i)获取column 字段名称，报下标异常

因为for循环的问题

查看追溯getColumnName源码，可以看到获取column之前，都 调用了getField method，可以看到getField方法中，columnIndex 是从1开始，不在范围都抛出异常，因此for循环以0开始，当然下标异常

最后贴一段映射赋值的代码

	// clazz就是实体对象

    public static T mapperGetValue(Class clazz,ResultSet resultSet) throws SQLException {
        T instance = null;
        try {
            instance = clazz.newInstance();
        } catch (InstantiationException | IllegalAccessException e) {
            e.printStackTrace();
        }

        ResultSetmetaData metaData = resultSet.getmetaData();
        for (int i = 1; i <= metaData.getColumnCount(); i++) {
            PropertyDescriptor propertyDescriptor = null;
            try {
                String column = metaData.getColumnName(i);
                String attr = lineToHump(column);
                propertyDescriptor = new PropertyDescriptor(attr, clazz);
            } catch (IntrospectionException e) {
                e.printStackTrace();
            }
            assert propertyDescriptor != null;
            Method writeMethod = propertyDescriptor.getWriteMethod();

            try {
                writeMethod.invoke(instance,resultSet.getObject(metaData.getColumnName(i)));
            } catch (IllegalAccessException | InvocationTargetException e) {
                e.printStackTrace();
            }
        }

        return instance;
    }

    private static Pattern linePattern = Pattern.compile("_(\w)");

    
    public static String lineToHump(String str) {
        str = str.toLowerCase();
        Matcher matcher = linePattern.matcher(str);
        StringBuffer sb = new StringBuffer();
        while (matcher.find()) {
            matcher.appendReplacement(sb, matcher.group(1).toUpperCase());
        }
        matcher.appendTail(sb);
        return sb.toString();
    }