First CodeRetreat in Poznań

On 15th January I had a pleasure to participate in first Code Retreat in Poznań. The event was organised by Adam Dudczak and Poznań JUG. If you don't know what Code Retreat is, take a look here. It is a great opportunity to meet other coders, see how they work and exchange knowledge and experience. There were 5 sessions, and the pairs were changing each time, so everyone coded with 5 different people.

Idea of Code Retreat is not only to code in pairs but also to use TDD. After lunch, during break, there were two discussion groups, one discussing BDD, and the other pair programming. I joined BDD group. First it was explained what BDD is, then we were discussing. The group was very active, many people had questions but there were also many answers :)

Programming task was standard for Code Retreats - Conway's Game Of Life. It's nice to watch development. During the first session we didn't finish our task, like most pairs. We barely started when the time was over. After the third session, most pairs had Game Of Life algorithm finished. Of course together with tests :)

Such an event is not only opportunity to learn, but also to meet people. Some I already knew from twitter, blogs etc., some from other events, and some were completely new to me. There was time to talk, not only during quite short breaks between sessions, but also during lunch and "afterparty". For lunch there was not pizza, but some decent dish, huge and tasty.

I have to write also about the place the event was held at. It was in Cognifide offices, and it was one of the nicest offices I've ever seen! Lunch and afterparty was in the basement, but this basement looked like a decent pub. Brick walls and ceilings, bar, comfy sofas and tables. There was also refrigerator full of beer, and it was used during afterparty :)

For me this event was a big success. Congrats, organizers!

Scala script to find duplicate files

Here is simple Scala script finding duplicate files and moving them to another directory. It searches album-with-duplicates for duplicates of files in main-album. All duplicates found are moved to copies directory in user's home.

If you have some ideas how to improve it, I'd appreciate if you share it in comments.

MD5 algorithm taken from here.

package com.blogspot.pawelstawicki.remove.duplicates

import java.security.MessageDigest
import java.io.{FileInputStream, File}
import org.apache.commons.io.{FilenameUtils, FileUtils, IOUtils}

/**
 * @author ${user.name}
 */
object App {
  
  def main(args : Array[String]) {
    val dir1 = new File("/photos/main-album,");
    val dir2 = new File("/photos/album-with-duplicates");

    val dir1Content = getAllFiles(dir1)
    val dir2Content = getAllFiles(dir2)

    var dir1Map = Map[String, File]()
    dir1Content.foreach(f => {
      val md5 = md5SumString(IOUtils.toByteArray(new FileInputStream(f)))
      println("md5 for " + f.getPath + ": " + md5)
      dir1Map = dir1Map + (md5 -> f)
    })

    var dir2Map = Map[String, File]()
    dir2Content.foreach(f => {
      val md5 = md5SumString(IOUtils.toByteArray(new FileInputStream(f)))
      println("md5 for " + f.getPath + ": " + md5)
      dir2Map = dir2Map + (md5 -> f)
    })

    for(md51 <- dir1Map.keys; md52 <- dir2Map.keys) {

      if (md51.equals(md52)) {
        val suspectedDuplicate = dir2Map(md52)
        val original = dir1Map(md52)

        if (checkDuplicate(original, suspectedDuplicate)) {
          println(suspectedDuplicate.getPath + " is duplicate of " + original.getPath)
          val copiesDir = new File(FileUtils.getUserDirectory + "/copies/" + FilenameUtils.getPathNoEndSeparator(original.getAbsolutePath()));
          println("Moving to " + copiesDir.getPath)
          FileUtils.moveFileToDirectory(suspectedDuplicate, copiesDir, true)
        }
      }
    }
  }

  def checkDuplicate(f1: File, f2: File): Boolean = {
    val bytes1 = new Array[Byte](1024*1024)
    val bytes2 = new Array[Byte](1024*1024)

    val input1 = new FileInputStream(f1)
    val input2 = new FileInputStream(f2)

    var bytesRead1 = input1.read(bytes1)
    while(bytesRead1 > 0) {
      val bytesRead2 = input2.read(bytes2)

      if (bytesRead1 != bytesRead2) {
        return false;
      }

      //Bytes read number the same
      if (!bytes1.sameElements(bytes2)) {
        return false
      }

      bytesRead1 = input1.read(bytes1)
    }

    //bytesRead1 is -1. Check if bytes read number from file2 is also -1
    if (input2.read(bytes2) == -1) {
      return true;
    } else {
      return false;
    }
  }

  def md5SumString(bytes : Array[Byte]) : String = {
    val md5 = MessageDigest.getInstance("MD5")
    md5.reset()
    md5.update(bytes)

    md5.digest().map(0xFF & _).map { "%02x".format(_) }.foldLeft(""){_ + _}
  }

  def getAllFiles(dir : File) : List[File] = {
    var l = List[File]()
    dir.listFiles.foreach(f => {
      if (f.isFile) {
        l = f :: l
      } else {
        l = l ::: getAllFiles(f)
      }
    })

    l
  }

}

JSF2.0 component for cross-field validation

Have you ever had problems with cross-field validation in JSF? Me too, so I created this component. You can validate few UIInput components and have their values as List in validator. The component is in softwaremill-faces library. To use it in maven project, add repository:

<repository>
  <url>http://tools.softwaremill.pl/nexus/content/groups/smlcommon-repos/ </url>
  <layout>default</layout>
  <releases>
    <enabled>true</enabled>
  </releases>
  <snapshots>
    <enabled>true</enabled>
  </snapshots>
</repository>

and dependency:

<dependency>
  <groupId>pl.softwaremill.common</groupId>
  <artifactId>softwaremill-faces</artifactId>
  <version>43-SNAPSHOT</version>
</dependency>

Now you can use multiValidator component. First add namespace to your .xhtml page:
xmlns:v="http://pl.softwaremill.common.faces/components"

Then just wrap components you want to cross-validate in <v:multiValidator>. If you attach validator to this component, value parameter that goes to validation method is List of values of UIInput components inside  tag.

E.g. if you want to validate two checkboxes. Each can be checked or unchecked, but at least one has to be checked.

<v:multiValidator id="multi" validator="#{bean.validationMethod}">
  <h:selectBooleanCheckbox value="#{bean.check1}" />
  <h:selectBooleanCheckbox value="#{bean.check2}" />
</v:multiValidator>
<h:message for="multi" />

Validation method in bean:

public void validationMethod(FacesContext context, UIComponent component, Object value) {
  List<Object> values = (List<Object>) value;
  //value is list of values of both selectBooleanCheckboxes
  Boolean firstChecked = (Boolean) values.get(0);
  Boolean secondChecked = (Boolean) values.get(1);

  if (! (firstChecked || secondChecked)) {
    Message message = new FacesMessage(FacesMessage.SEVERITY_ERROR, "Check at least one checkbox", null);
    throw new ValidatorException(message);
  }
}

If none checkbox is checked error message is displayed in <h:message for="multi"> tag.

Source code of this component is on github.

Any suggestions, opinions or questions regarding this component are welcome. Have a good time using it :)

GWT table row as UiBinder

Some time ago I wanted to dynamically add rows to a table in GWT, but I wanted to define row template using UiBinder. Programatically it is no problem. You can create FlexTable and add widgets to it. The problem arises when you want to do it using UiBinder. You can create a FlexTable in UiBinder, and you can create widgets, but you can't create element which renders to html tag <tr>. Kazik Pogoda found a way to do it.

First we need two widgets which renter to <tr> and <td>. The code for TR:

public class TrElement extends ComplexPanel {
  private TableRowElement tr;

  public TrElement() {
    Document doc = Document.get();
    tr = doc.createTRElement();
    setElement(tr);
  }

  @Override
  public void add(Widget child) {
    add(child, (Element) tr.cast());
  }
}

The TD is analogous, just change TableRowElement into TableCellElement and doc.createTRElement() into doc.createTDElement(). We can now create UiBinder xml file which renders to single table row (TR element is it's root):

<!DOCTYPE ui:UiBinder SYSTEM "http://dl.google.com/gwt/DTD/xhtml.ent">
<ui:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder"
      xmlns:g="urn:import:com.google.gwt.user.client.ui"
      xmlns:my="urn:import:pl.my.gwt.client">
 
  <my:TrElement>
    <my:TdElement>
      <g:HTMLPanel>
        <g:Label ui:field="icon" styleName="Icon"></g:Label>
        <g:Label ui:field="title" styleName="Title"></g:Label>
        <g:Label ui:field="description" styleName="Description"></g:Label>
      </g:HTMLPanel>
    </my:TdElement>
    <my:TdElement>
      <g:Label ui:field="price" styleName="Price"></g:Label>
    </my:TdElement>
  </my:TrElement>
</ui:UiBinder>

Here is how we can use it to add to a table (FlexTable):

TableRowView trView = new TableRowView();
table.getElement().appendChild(trView.getElement());

Warsjawa 2010. Impressions.

My impressions after this year's Warsjawa are very positive. Well, in fact I could expect this :) Presentations were interesting, meeting other IT people is always good too. I met Bartek Zdanowski, who wanted to meet me. It's quite strange feeling when you meet somebody who knows you, but didn't meet you before. Strange but nice :)

First presentation was about Play framework by Wojciech Erbetowski. I was a little late, but I've seen enough to notice that Play is framework different than all the others.

I was a bit disappointed that Sławek Sobótka didn't make it there (he fell ill). He's topic was the most interesting for me. However, Paweł Lipiński worthily replaced him. Paweł was talking about what in programming he was taught by... his own children, kindergarten, Roomba etc. I never noticed that when there are 2-3 people in a project, it is much cleaner, but it's becoming a mess when there are more than 5 people. I never noticed it, but now it's very clear to me. It seems Paweł is a man who can learn and get knowledge from anything. Ah, and he mentioned me :)

This year on Warsjawa there was also something from our Szczecin JUG. Darek "Lock" Łuksza presented Git version control system and it's Eclipse plugin EGit. Darek did great job, and even found one bug during presentation :) It seemed a bit embarassing for him, but the rest was very good. He knows the topic very well (he's EGit commiter) and he showed many things coding live. Overall presentation was very good.

After Darek's presentation pizza arrived. It disappeared quite quickly, maybe there was a bit too few. We run out of beverages too. Anyway I didn't hear somebody died of hunger or thirst, so it wasn't that bad :)

Next interesting presentation was about Clojure. This time there were two presenters. First Marcin Rzewucki showed us some theory, then Jan Rychter told about practical use of Clojure in Fablo. He showed few interesting features of this language, like STM. Thanks to STM in Fablo they are able to replace customer's database without stopping the service. Pretty impressive.

Did you know that in Java you can have two methods with the same name and arguments, differing only by return type? Compiler can't compile this, but if you write it in bytecode it is perfectly valid! This and others interesting things about bytecode were shown by Adam Michalik. I wonder if any company needs "bytecode programmer"? I like such low-level stuff. At the university I always liked assembler.

The last presentation by Rafał Rusin was about Apache HISE. I have to admit I was too tired and the topic was not very interesting for me, so I didn't remember much from this one.

Generally I think this was very nice conference. Meeting new people, and some older friends, is always nice. Listening to interesting people talking about interesting things is also nice. It seems one hour for presentation is very good duration. All the presenters could do all they wanted/needed (at least it seemed so). I remember on GeeCON there was only 45 minutes and it was too little. If only there was more pizza (or maybe something better?) and beverages it would be perfect.

Convert JME application to Android

Here is the story:

I bought Android phone. Earlier I was using Windows Mobile phone, and I had one j2me application on it that was very important to me. It was "TokenGSM", application which serves the same purpose as RSA tokens, but installed on my phone. Very good decision of my bank that they created it so users don't have to carry additional device with them (users have choice, you can also get RSA token if you prefer it). So this application is necessary if I want to log in to my bank account. Pretty vital.

But, as you probably know, there is no Java ME on Android :( Here is what I did (this forum was useful):

1. Call the bank and ask for new GSM token. Token is somehow bound to the phone, so if you change phone, you need new token.
2. Write down URL from WAP Push SMS. Do it before opening it. On my phone (Android 2.2, HTC Desire) if you don't do it but just try to open URL, it's lost. Browser can't open it, but you don't even have chance to see it. Browser just blinks and returns to home screen :| It's not in history, nor in downloads.
3. Go to http://www.netmite.com/android/ and download App Runner. I went there from my phone and downloaded directly to it. I'm not sure if this point is really necessary, but some say it is.
4. Click "Convert existing j2mes into apk & upload to Android Market." I don't think it really uploads to Market.
5. Enter your written down URL and click "Get Apk". You have your Android TokenGSM :)
6. Transfer the file to your phone and install it.
7. Now you have to activate the token with code you received from the bank.

Flash scope in JSF 2.0 (nothing about Adobe Flash)

In JSF 2.0, amongst Request, Session etc, there is the new scope called Flash. (However there is no annotation @FlashScope, and you can't put bean in this scope). It's concept is taken from Ruby on Rails. Data in Flash scope are available for current and for next request, but not for subsequent requests. Usage is very simple.
On first page (e.g. index.html):

<h:form>
  <h:inputtext value="#{flash.text}">
  <h:commandbutton action="page?faces-redirect=true" value="To page">
</h:form>

And this is the page we are redirecting to, page.xhtml:

<h:form>
  <h:outputtext value="#{flash.text}">
</h:form>

Why would you need such scope? Imagine you want to enter data on one page, then redirect to another page, and display this data. If not for redirect, we could use Request scope. But with redirect value is sent with request, then browser is redirected to another page, and makes another request. Request scoped value is gone. In such case Flash scope becomes useful. We can put value in this scope with one request, and when another request is made, the value is still there. But it is not stored in session, and is not available for subsequent requests.

However, there is a way to make data in Flash scope alive a bit longer. It is enough if in page.xhtml we change #{flash.text} to #{flash.keep.text}. This way data is not removed from the scope after first request, but is available for one more.

In managed beans, you can get flash scope by

Flash flash = FacesContext.getCurrentInstance().getExternalContext().getFlash();