The Holy Java

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Archive for March, 2014

Most interesting links of March ’14

Posted by Jakub Holý on March 31, 2014

Recommended Readings

Clojure Corner

  • Timo Mihaljov’s Pimp My REPL (3/2014)- really great tips – user.clj, :dev profile, user-wide config in .lein/profiles.clj, tools.namespace, making funs available everywhere & more via Vinyasa, form println with Spyscope, debug-repl, difform, clj-ns-browser


  • clj-ds – Clojure immutable datastructures extracted from Clojure and made easier for use directly in Java

Favourite Quotes

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Framework Joy: Load in Hibernate Updates Data

Posted by Jakub Holý on March 31, 2014

Would you ever guess that this line

// Load Buyer from DB by id using Spring's HibernateTemplate:
final Buyer traveller = (Buyer) hibernateTemplate.load(Buyer .class, new Long(id));

could lead to a constraint-validation exception during a batch update or delete and re-insert rows (loosing all columns Hibernate does not know about)? I was quite surprised.

In particular buyer’s bonusCards get deleted and re-inserted, because Hibernate believes that the collection of cards is dirty, even though it has just loaded it from the DB. I am not exactly sure why (preventing false positives in dirty checks requires some black magic), this is the configuration:

<class name="Buyer" ...>
    <set name="bonusCards " table="bonus_cards">
        <key column="buyer_id"/>
        <composite-element class="BonusCard">
            <property name="number" column="number" not-null="false"/>
            <property name="expiredate" column="expdate"/>

Of course Hibernate certainly has good reasons to update and delete+re-insert data upon load and we could certainly get rid of (some of) these updates by configuring Hibernate better. But it still demonstrates nicely the hidden cost of using a complex framework – in this case, it behaves quite unexpectedly and requires extensive knowledge to set up properly and to troubleshoot.

Posted in j2ee | Tagged: | Comments Off on Framework Joy: Load in Hibernate Updates Data

How To Generate A Valid Credit Card Number For A Bin (First 6 Digits)

Posted by Jakub Holý on March 25, 2014

There is plenty of generators that can produce numbers that are valid credit card numbers according to the Luhn check and specific rules of the individual issuer companies. However I have not found anything that would generate the missing digits given a bin, i.e. the first 6 digits of a credit card (the “bank identification number”). So I created one, reverse-engineering org.apache.commons.validator.routines.CreditCardValidator from common-validator 1.4:

// Groovy:
/** Map RegExp from C.C.Validator to the total length of the CC# */
binReToLen = [
        (~/^(3[47]\d{0,13})$/) : 13+2, // amex
        (~/^30[0-5]\d{0,11}$/) : 11+3, // diners 1
        (~/^(3095\d{0,10})$/) : 10+4, // diners 2
        (~/^(36\d{0,12})$/) : 12+2,     // diners 3
        (~/^|3[8-9]\d{0,12}$/) : 12+2,  // diners 4
        (~/^(5[1-5]\d{0,14})$/) : 14+2, // master
        (~/^(4)(\d{0,12}|\d{15})$/) : 12+1 // visa
        // Discover cards omitted

/** Bin is e.g. 123456 */
def completeCCn(String bin) {
    def ccnFill = "1" * 19
    int ccnLen = lenForBin(bin)

    def ccnWithoutCheck = bin + ccnFill[0..<(ccnLen - 6 - 1)] // - bin, - check digit

    def check = computeLuhncheckDigit(ccnWithoutCheck)

    return "$ccnWithoutCheck$check"

def lenForBin(String bin) {
    def match = binReToLen.find { it.key.matcher(bin).matches() }
    if (match == null) {
        throw new RuntimeException("Bin $bin does not match any known CC issuer")

def computeLuhncheckDigit(def ccnWithoutCheck) {

completeCCn('465944') // => 4659441111118

Testing FTW!

Posted in General, Languages, Testing | Tagged: , | Comments Off on How To Generate A Valid Credit Card Number For A Bin (First 6 Digits)

HttpServletRequest: requestURI/requestURL/contextPath/servletPath/pathInfo/queryString

Posted by Jakub Holý on March 24, 2014

I never remember what some of these HttpServletRequest methods return so here is an example:

- requestURL  = http://localhost:8080/myapp/users/profile.xhtml
- requestURI  = /myapp/users/profile.xhtml = contextPath + servletPath + pathInfo
- contextPath = /myapp = the first segment after hostname (unless the app runs and the root app with context /)
- servletPath = /users/profile.xhtml (part after contextPath to the servlet that handled the request)
- pathInfo    = null (what remains after servletPath up to the queryString; would return '/dummy' if the url was '.../profile.xhtml/dummy?id=007')
- queryString = id=007

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Ansible: Best practices for deriving host-level var from a group var

Posted by Jakub Holý on March 19, 2014

I have a cluster and a group variable (in test/staging/prod) holding the hostname of the cluster master. For each host, I want to derive a variable which is set to either “slave” or “master” and use it in templates.

This can be done with set_fact:

# group_vars/staging:


# roles/xxx/tasks/main.yml:
- name: Set default jboss_host_type
  set_fact: jboss_host_type=slave
- name: Set jboss_host_type to master if master
  set_fact: jboss_host_type=master
  when: jboss_master_host == inventory_hostname

We could simplify that by using more advanced Jinja:

# roles/xxx/tasks/main.yml:
- name: Set jboss_host_type var
  set_fact: jboss_host_type={{ 'master' if jboss_master_host == inventory_hostname else 'slave' }}

but it is preferred not to use logic coded in Jinja2.

// Ansible 1.5.3

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Frustration-Driven Development – Towards DevOps, Lean, Clojure

Posted by Jakub Holý on March 17, 2014

A post about development practices, speed, and frustration.

My wife has mentioned that she likes my passion for doing things right in software development. That made me thinking, why do I actually care so much and do not just enjoy the coding itself? It boils down to that I am not happy until my code is in production. Seeking the satisfaction of having my code used by and helping people while trying to eliminate all unnecessary mental drain is behind all the practices that I embrace and evangelize. It’s a drug I like to take often, in small doses.

practices = f(max(delivered value), min(mental energy))

So how does this relate to DevOps, Continuous Delivery, testing, single-piece-flow, Lean Startup, Clojure? It is simple.

Read the rest of this entry »

Posted in SW development | Tagged: | 1 Comment »

Recursive Copy In Ansible 1.5 And –diff

Posted by Jakub Holý on March 5, 2014

Ansible 1.5 has partial support for recursive copy of files:

  • the synchronize module, using rsync
    • cons: does not support group=, owner=
    • -C and –diff – it does not print diff of the files changed; when running ansible with -v, it will print output of rsync’s –itemize-changes, i.e., for each changed file/dir, something like “<…… conf/httpd.conf\n” (< = file uploaded, s = size changed, t = timestamp changed, . = this attribute has not been changed)
  • the copy module
    • -C –diff – it only reports “changed” without naming the changed files or showing diffs (unless there is only one changed file)
  • the local_action module, used to run rsync manually (essentially the same as synchronize but more control)
  • So the only way to do a kind of recursive copy with working diff is to use copy with with_fileglob for each directory and subdirectory 😦

To check differences (without diff) manually:

rsync -e ssh -vrnc --itemize-changes source/dir myuser@myserver:/opt/dest/

where v= verbose, r = recursive, n = dry-run, c = check based on checksum, not timestamp+size; a typical output for a changed file is <fcsT...... httpd.conf (< = to be uploaded, f = it is a file, c = checksum differ, s = size differ, T = timestamp would be updated).

Posted in Tools | Tagged: , | Comments Off on Recursive Copy In Ansible 1.5 And –diff

Petitioning EU to act against Russian aggression in Ukraine

Posted by Jakub Holý on March 5, 2014

join the campaignAs a citizen of a country that has been invaded by Hilter in 1938 under the pretext of protecting local Germans and again invaded by Russia in 1968, I cannot watch another such invasion and annexation taking place in Europe while EU does little of any consequences.

Please consider signing the petition to EU to act against Russian aggression with all the political and economical power it has, even if – oh the horror – will cost our wallets too.

Click here to join:
European Union, Catherine Ashton, Herman van Rompuy: Act on Ukraine. Immediately!

Posted in Uncategorized | 4 Comments »

Ansible Troubleshooting Tips

Posted by Jakub Holý on March 4, 2014

Few tips for troubleshooting Ansible, based on my brief experiences with Ansible 1.4 (read: do not rely on this info too much).

Run ansible-playbook in the verbose mode

ansible-playbook -vvvv ... will provide you with plenty of details of what is going on. (Notice that additional v:s, starting from none, add more detail.)

Use ./hacking/test-module

Check out Ansible sources and use the ./hacking/test-module script – see Developing Modules.

Read the rest of this entry »

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