Friday, September 25, 2009

Building regular expressions in Groovy

Because of compact syntax regular expressions in Groovy are more readable than in Java. Here is how Jeffrey Friedl's example would look like in Groovy:

def subDomain  = '(?i:[a-z0-9]|[a-z0-9][-a-z0-9]*[a-z0-9])' // simple regex in single quotes
def topDomains = """
(?x-i : com \\b # you can put whitespaces and comments
| edu \\b # inside regex in eXtended mode
| biz \\b
| in(?:t|fo) \\b # but you have to escape
| mil \\b # backslashes in multiline strings
| net \\b
| org \\b
| [a-z][a-z] \\b

def hostname = /(?:${subDomain}\.)${topDomains}/ // variable substitution in slashy strings

def NOT_IN = /;\"'<>()\[\]{}\s\x7F-\xFF/ // backslash is not escaped in slashy strings
def NOT_END = /!.,?/
def ANYWHERE = /[^${NOT_IN}${NOT_END}]/
def EMBEDDED = /[$NOT_END]/ // you can ommit {} around var name

def urlPath = "/$ANYWHERE*($EMBEDDED+$ANYWHERE+)*"

def url =

# match the hostname part
(?: ftp | http s? ): // [-\\w]+(\\.\\w[-\\w]*)+

# allow optional port
(?: :\\d+ )?

# rest of url is optional, and begins with /
(?: $urlPath )?

assert '' ==~ url

As you can see, there are several options, and for every subexpression you can choose the one that's more expressive.


• Martin Fowler on composed regexes
• Pragmatic Dave on regexes in Ruby
• Feature request to make regexes even groovier
• Mastering Regular Expressions — best regex book
• Groovy Pattern and Matcher classes

Tuesday, September 22, 2009

Fill parameters in LCDS Assembler methods

Last few days we spent debugging some nasty bug in the code that uses LiveCycle managed collections. We were adding/removing items to/from collections on the server side. We saw that server sent a message to the client, client did receive the message, but then it ignored it and didn't update the collection (data grid). After digging into the client side logs we found the reason of such a misbehaviour.

If you have two destinations that share the same channel

<service id="data-service" class="">
<destination id="MyFirstDestination">
<channel ref="my-rtmp-channel"/>
<destination id="MySecondDestination">
<channel ref="my-rtmp-channel"/>

LCDS uses fillParameters as a key in the managed collections cache. That means fillParameters must be immutable.

public class MyFirstAssembler extends {

public int refreshFill(List fillParameters, Object newItem, boolean isCreate, Object oldItem, List changes) {
// Never change fillParameters!

public Collection fill(List fillParameters) {
// Never change fillParameters!

Adobe documentation says nothing about this, so keep this rule in mind when working with LCDS managed collections.


• Flex log viewer