com.atlassian.scheduler.caesium.cron.parser
Class CronExpressionParser

java.lang.Object
  com.atlassian.scheduler.caesium.cron.parser.CronExpressionParser

public class CronExpressionParser
extends Object

Parser for cron expressions.

Strictly speaking, "names" are only permitted in the month and day-of-week fields; however, to simplify the parser, they are accepted by the parser and the field type fails to resolve them, instead.

Tokens are collected by CronLexer. Although a few special cases exist to help maintain compatibility with Quartz, the EBNF looks something like this:

 
 (* ========================================================= *)
 (*  Basic syntax available to all fields, like 2-7,9 or */3  *)
 (*  English names and ranges, like MON,WED,FRI or APR-SEP    *)
 (*  are also included here.                                  *)
 (* ========================================================= *)
 
 slash_interval = SLASH , NUMBER
 
 number_range = NUMBER , HYPHEN , NUMBER , [ slash_interval ]
 
 name_range = NAME , HYPHEN , NAME , [ slash_interval ]
 
 number_expression = number_range , [ slash_interval ]
                   | NUMBER , [ slash_interval ]
 
 name_expression = name_range
                 | NAME , [ slash_interval ]
 
 asterisk_expression = ASTERISK , [ slash_interval ]
 
 simple_expression = name_expression
                   | number_expression
                   | asterisk_expression
                   | slash_interval  (* implied asterisk *)
 
 simple_field = simple_expression , { COMMA , simple_expression }
 
 (* ========================================================= *)
 (*  Special syntax for day-of-month, like 15W or L-3W        *)
 (* ========================================================= *)
 
 special_dom_last_offset_number = NUMBER , [ FLAG_W ]
 
 special_dom_last_offset = special_dom_last_offset_number
 
 special_dom_last_weekday = FLAG_W
 
 special_dom_last = FLAG_L , HYPHEN ,  special_dom_last_offset
                  | FLAG_L , special_dom_last_weekday
                  | FLAG_L
 
 special_dom_weekday = FLAG_W
 
 special_dom_field = special_dom_last
                   | special_dom_weekday
 
 (* ========================================================= *)
 (*  Special syntax for day-of-week, like 6#3 or 4L           *)
 (* ========================================================= *)
 
 special_dow_nth = HASH , NUMBER
 
 special_dow_name = NAME , special_dow_nth
 
 special_dow_number = NUMBER , special_dow_nth
                    | NUMBER , FLAG_L
 
 special_dow_field = special_dow_name
                   | special_dow_number
                   | FLAG_L   (* Synonymous with "7" when by itself like this *)
 
 (* ========================================================= *)
 (*  Field definitions                                        *)
 (* ========================================================= *)
 
 second_field = simple_field
 
 minute_field = simple_field
 
 hour_field = simple_field
 
 dom_field = special_dom_field
           | simple_field
 
 month_field = simple_field
 
 dow_field = special_dow_field
           | simple_field
 
 year_field = [ simple_field , [ WHITESPACE , { (* any sequence of unparsed tokens *) } ]
 
 (* ========================================================= *)
 (*  Full expression grammar                                  *)
 (* ========================================================= *)
 
 second_minute_hour = second_field , WHITESPACE, minute_field , WHITESPACE , hour_field , WHITESPACE
 
 qm_month_dow = QUESTION_MARK , WHITESPACE , month_field , WHITESPACE , dow_field
 
 dom_month_qm = dom_field , WHITESPACE , month_field, WHITESPACE , QUESTION_MARK
 
 dom_month_dow = qm_month_dow
               | dom_month_qm
 
 cron_expression = [ WHITESPACE ] , second_minute_hour , dom_month_dow , [ WHITESPACE , year_field ] ;
 
 

Since:

v0.0.1

Method Summary

static boolean	isValid(String cronExpression) Returns true if parse(String) will succeed; false if it will report a syntax error.
static CronExpression	parse(String cronExpression) Parses the supplied cron expression into a form that can evaluate it against candidate dates or find the next time that it matches.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

parse

public static CronExpression parse(String cronExpression)
                            throws com.atlassian.scheduler.cron.CronSyntaxException

Parses the supplied cron expression into a form that can evaluate it against candidate dates or find the next time that it matches.

Parameters:

cronExpression - the cron expression to parse

Returns:

the parsed form of the cron expression

Throws:

com.atlassian.scheduler.cron.CronSyntaxException - if there is a problem with the cron expression

isValid

public static boolean isValid(String cronExpression)

Returns true if parse(String) will succeed; false if it will report a syntax error.

Parameters:

cronExpression - the cron expression to parse

Returns:

true if parse(String) will succeed; false if it will report a syntax error.