Developer Blogging

Git Series: Installing Git on Windows

2014-12-15T17:17:00.000-06:00

You have a “next, next, ok” installer, just be aware of:

I haven’t found any problem selecting “Use Git and optional Unix tools from the Windows Command Prompt” but the safest option is “Use Git from Git Bash”

In UNIX systems the end of a line is represented with a line feed (LF). In windows a line is represented with a carriage return (CR) and a line feed (LF) thus (CRLF). Most of the open source projects use UNIX environments so go along with the first option. Select “Checkout as-is, commit as-is” if EVERYONE in your team is going to work in a Windows Environment

There are two ways to configure git:
Modifying files:

C:\Program Files (x86)\Git\etc\.gitconfig     # System level

$HOME\.gitconfig        # User level

repository\.git\config    # Repository level

Using commands

git config --system   # System level

git config --global    # User level

git config   # Repository level

Minimal

git config --global user.name “Xavier Figueroa”

git config -- global user.email “example@devm.com”

git config --list

user.name=Xavier Figueroa

user.email=example@devm.com

git config user.name

Given that you already have the git bash installed, you can use linux commands
.gitconfig is hidden, so in order to see the file you need to use ls –a
xavi ~ $ ls -a

To see the content you can use

xavi ~ $ cat .gitconfig

xavi ~ $ tail .gitconfig

xavi ~ $ vim .gitconfig

Set Default Text Editor

Install your favorite editor (Sublime, notepad++, atom)

git config --global core.editor "'c:/program files/sublime text 3/subl.exe' -w"
or
git config --global core.editor "atom --wait"

If you have problems you can try editing the .gitconfig file and use:
editor = 'C:\\Program Files\\Sublime Text 3\\subl.exe' -w

You can also set the GIT_EDITOR, VISUAL, or EDITOR environment variables.

Auto-Completion

In windows is provided by default, but if it is not working you can try:
Edit/create $HOME\.bashrc or $HOME\.bash_profile

if [ -f 'C:\Program Files (x86)\Git\etc\git-completion.bash' ]; then

    source 'C:\Program Files (x86)\Git\etc\git-completion.bash'

fi

Improve the bash

Edit/create $HOME\.bashrc or $HOME\.bash_profile

if [ -f 'C:\Program Files (x86)\Git\etc\git-prompt.sh' ]; then

     source 'C:\Program Files (x86)\Git\etc\git-prompt.sh'

fi

green="\[\033[0;32m\]"

cyan="\[\033[1;36m\]"

purple="\[\033[1;35m\]"

reset="\[\033[0m\]"

export GIT_PS1_SHOWDIRTYSTATE=true

export GIT_PS1_SHOWUNTRACKEDFILES=true

export PS1="$purple\u$green\$(declare -F __git_ps1 &>/dev/null && __git_ps1 ' (%s)')$cyan \W $ $reset"

Getting help

Pressing space or f will move you forwards or pressing b will move you backwards as well
Pressing q stands for Quit will take you back to the command line

References:
http://blog.devm.org
http://git-scm.com/downloads
https://help.github.com/articles/set-up-git/
http://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration
https://help.github.com/articles/associating-text-editors-with-git/
http://www.cyberciti.biz/tips/howto-linux-unix-bash-shell-setup-prompt.html

Git Series: Installing Git on Linux

2014-12-15T02:02:00.000-06:00

See the 3:45 min video here

If you are using Fedora 21 Workstation like me jump to step 5 ;)

1 Installation

If you’re on Fedora-based, you can use yum:
$ yum install git
If you’re on a Debian-based distribution like Ubuntu, try apt-get:
$ apt-get install git
Configuration
There are two ways:

Modifying files

/etc/.gitconfig        # System level
 ~/.gitconfig          # User level
 Repository/.git/.gitconfig   # Repository level

Using commands

git config --system # System level
 git config –global    # User level
 git config            # Repository level

2 Minimal

git config --global user.name “Xavier Figueroa”
 git config -- global user.email “example@devm.com”
 git config --list
 user.name=Xavier Figueroa
 user.email=example@devm.com
 git config user.name

.gitconfig is hidden, so in order to see the file you need to use ls –a
xavi ~ $ ls -a

To see the content you can use

xavi ~ $ cat .gitconfig
 xavi ~ $ tail .gitconfig
 xavi ~ $ vim .gitconfig

3 Set Default Text Editor

git config --global core.editor "vim -w"
or set the GIT_EDITOR, VISUAL, or EDITOR environment variables.

4 Auto-Completion

curl -OL https://raw.githubusercontent.com/git/git/master/contrib/completion/git-completion.bash
 curl -OL https://raw.githubusercontent.com/git/git/master/contrib/completion/git-prompt.sh

Rename file

mv ~/git-completion.bash ~/.git-completion.bash
 mv ~/ git-prompt.sh ~/ .git-prompt.sh

Edit ~/.bashrc

if [ -f ~/.git-completion.bash ]; then
 source ~/.git-completion.bash
 fi
 if [ -f ~/.git-prompt.sh ]; then
 source ~/.git-prompt.sh
 fi

5 Improve the bash

Add the following ~/.bashrc


 if [ -f /usr/share/git-core/contrib/completion/git-prompt.sh ]; then
 source /usr/share/git-core/contrib/completion/git-prompt.sh
 fi
 green="\[\033[0;32m\]"
 cyan="\[\033[1;36m\]"
 purple="\[\033[1;35m\]"
 reset="\[\033[0m\]"
 export GIT_PS1_SHOWDIRTYSTATE=true
 export GIT_PS1_SHOWUNTRACKEDFILES=true
 export PS1="$purple\u$green\$(declare -F __git_ps1 &>/dev/null && __git_ps1 ' (%s)')$cyan \W $ $reset"

6 Getting help

git help to see the list of commands
git help <specific command> to see how to use the command
Pressing space or f will move you forwards or b pressing b will move you backwards as well
Pressing q stands for Quit will take you back to the command line

References
blog.devm.org
http://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration
https://help.github.com/articles/associating-text-editors-with-git/
http://www.sublimetext.com/3

Fedora 21 Guest in Windows Host using VirtualBox

2014-12-13T12:47:00.000-06:00

I created a gallery to show you how to start working with Fedora using Virtual Box
In my VM I have:
2GB RAM
2 Processors
64MB In video Memory with 3D Acceleration Enabled
Virtual Disk with 20GB dynamically allocated.

See the gallery here

Everything is working just fine, this is the first time that I can install and start working without major problems. I'm very glad with this new version of Fedora so far

References:
https://getfedora.org/en/workstation/
https://docs.fedoraproject.org/en-US/Fedora/21/html/Installation_Guide/
http://www.binarytides.com/vbox-guest-additions-fedora-20/
http://worldofgnome.org/installing-the-latest-virtualbox-guest-in-fedora/
http://blog.devm.org/?p=28

Git Series: Quick Intro

2014-12-12T13:42:00.001-06:00

Git is a software that keeps track of changes and allows you to move back and forth between different versions to compare and see what changed between each one. Git is a VCS (Version Control System). When a VCS is used to manage source code, it’s also called a SCM (Source code management) too

VCS + source code = SCM

Let’s look back

Source Code Control System (SCCS) 1972. Closed source, free, Only for UNIX. It stored the original file and all the changes that went after it, so when you opened the file, it opened the original one and then all the changes were applied (low performance)

Revision Control System (RCS) 1982. open source, cross platform. It kept the most recent file in its whole form with all the previous changes, and only if you want a previous version, you applied the change snapshot to go backwards in time (better performance)

Concurrent Version System (CVS) 1986. Open source, cross platform. You could work with multiple files. Many users could work with a single repository over a network, the concept of remote repositories were introduced.

Apache Subversion (SVN) 2000. Open source, cross platform. It was faster and allowed to save different file formats. It kept track of directories not only of files, SVN applied transactions to update changes through many files and directories and mantain integrity

Bitkeeper scm 2000. Closed source, cross platform. First distributed versions control, it had a community version used for source code of the Linux kernel. In 2005 the community version disappeared

Git 2005. Open source, cross platform. Developed by Linus Torvalds as a replacement for Bitkeeper

Distributed Version Control

Every user maintain their own repositories. Changes are stored as change sets or patches and every user tracks only the changes that are useful for them.

It is a convention to establish a “master” repository and stay up to date with this master repository, but it is just a convention, we don’t have to

No need to communicate with the central server (work offline), it allows you to work independently and then submit your changes for inclusion or rejection

Ignore files in Git

2014-11-26T14:24:00.001-06:00

In Terminal, navigate to the location of your Git repository and type
touch .gitignore
Check this collection of useful .gitignore templates
This file usually appears in the root of the repository, you can get the root directory using
git rev-parse --show-toplevel
However we can have this file in any sub folder.

To ignore files that was already tracked we need to remove them from the index, but first of all we need to Commit pending changes to avoid unexpected behavior
git rm -r --cached .
-r Allow recursive removal when a leading directory name is given.
-q git rm normally outputs one line (in the form of an rm command) for each file removed. This option suppresses that output.

git add .
git commit -am “Remove ignored files”
-a Tell the command to automatically stage files that have been modified and deleted, but new files you have not told Git about are not affected

If you get the warning

warning: LF will be replaced by CRLF in <file>The file will have its original line endings in your working directory.

You can simply use
git config core.autocrlf false
In Unix systems the end of a line is represented with a line feed (LF). In windows a line is represented with a carriage return (CR) and a line feed (LF) thus (CRLF). It’s nothing to worry about.

References
http://git-scm.com/docs/git-commit
https://help.github.com/articles/ignoring-files/
https://github.com/github/gitignore
http://git-scm.com/docs/gitignore

MediaWiki 1.22.6 on Fedora 20

2014-04-19T00:45:00.000-05:00

Motivation

As many of you probably know, the next version of Fedora is under many changes F21 is not going to be released earlier than in late October
yum in FC20 only allows to install the version 1.21.8 so in order to have the most recent version we need to Install it as an rpm package or Manually
It is very likely to have problems during the installation, the main problem that I had was related with SELinux, so I hope this post can help you to save some time and headaches ;-)

Prerequisites

I recommend to have a Linux Manual just in case

Install these packages

Open a Terminal and become root

su

yum install -y httpd mysql-server php php-pear php-xml php-mysql php-intl php-php-pecl-zendopcache-apc php-gd php-mbstring ImageMagick-perl mailcap

Configure Services

service mysqld start (service mariadb start)
mysql_secure_installation

*be aware of the database version, mysql was replaced by mariadb
As a good practice you should disable anonymous access and don't allow root access remotely to your database

service httpd start

To make sure that the servers automatically start at boot-up, type the following commands:

chkconfig mysqld on (chkconfig mariadb on)
chkconfig httpd on

-Installing Manually

Drop the tarball or a clone

git clone https://gerrit.wikimedia.org/r/p/mediawiki/core.git

in a directory accessible to your web server

/var/www/html/wiki/

-Installing it as an rpm package

Download mediawiki-1.22.6-1.fc21.noarch.rpm from rpmfind.net
*select apropiate architecture

yum localinstall /root/Downloads/mediawiki-1.22.6-1.fc21.noarch.rpm

MediaWiki is installed in

/usr/share/mediawiki

with files specific to a site installed in

/var/www/wiki which contains:
config/
config/index.php
images/
index.php

Files in /var/www/wiki are used as a template and Apache can only access /var/www/html if not modified. So run

cp -a /var/www/wiki /var/www/html

the skin (the design and the css and js and images of the wiki) are still in /usr/share/mediawiki/skins which is not accessible by web server.
Make them accessible:

cp -a /usr/share/mediawiki/skins /var/www/html/wiki
or
ln -s /usr/share/mediawiki/skins /var/www/html/wiki/skins

Running the Installer

Navigate to localhost/wiki with your favorite browser.
If you are accessing that page for the first time, it would ask you to setup the wiki.
Follow that link which should take you to the setup page.
Fill in everything and click install button.
Create a new Mysql user (suggested by the installer)
Fill if you want a database prefix.
if everything goes right, MediaWiki installation successful page will be displayed.
LocalSettings.php has to be moved from config/ directory to the parent directory.

mv /var/www/html/wiki/config/LocalSettings.php /var/www/html/wiki

Delete the config directory for security reasons.

rm -fr /var/www/html/wiki/config

and that´s it!! :D
I'm not an expert so if you have any comment, correction, addition, question just let me know ;)
I hope to upload a video in a few days so if you have a suggestion also let me know

Troublesutting

PHP source code in localhost/wiki
Restart your httpd server

Permission Denied error
The minimum required for the wiki files and directories is

chmod 644

so check using ls -l
Also, you may need to change SELinux configuration

setsebool -P httpd_read_user_content 1
setbebool -P httpd_enable_homedirs 1

more info about SELinux

References

http://www.mediawiki.org/wiki/Manual:Installation_requirements
http://www.mediawiki.org/wiki/Download_from_Git
http://www.mediawiki.org/wiki/Manual:Running_MediaWiki_on_Fedora
http://www.wikihow.com/Install-MediaWiki-on-Fedora
http://www.mediawiki.org/wiki/SELinux

java.lang.AbstractMethodError: org.apache.xerces.dom.DeferredElementImpl.getTextContent()

2013-04-16T13:26:00.003-05:00

org.w3c.dom.Node is an interface. org.apache.xerces.dom.DeferredElementImpl is an implementation of that interface. It seems that DeferredElementImpl does not implement getTextContent() properly. There are a lot of other implementations. If you write a program that uses DocumentBuilderFactory, then when you run it, you will actually be using one of the implementations.

You can choose between:

"com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl" Is the standard implementation bundled in the Sun JRE.
"org.apache.xerces.jaxp.DocumentBuilderFactoryImpl" The non-standard XML parser. Specified in a library on your classpath. That is perfectly fine, but it's something you should be aware of.

The method javax.xml.parsers.DocumentBuilderFactory#newInstance() uses the following ordered lookup procedure to determine the implementation class to load:. See Javadoc for details

Use the javax.xml.parsers.DocumentBuilderFactory system property.
Use the properties file "lib/jaxp.properties" in the JRE directory.
Use the Services API (as detailed in the JAR specification), if available, to determine the classname. The Services API will look for a classname in the file META-INF/services/javax.xml.parsers.DocumentBuilderFactory in jars available to the runtime.
Platform default DocumentBuilderFactory instance.

Setting the jaxp.debug system property will cause this method to print a lot of debug messages to System.err

java -Djaxp.debug=1 YourProgram .... or java -Djaxp.debug=true YourProgram ....

The method javax.xml.parsers.DocumentBuilderFactory#newInstance(String factoryClassName, ClassLoader classLoader) specifies the implementation class to load

How to find the JAXP implementations been used

private static void OutputJaxpImplementationInfo() {
   System.out.println(getJaxpImplementationInfo("DocumentBuilderFactory", DocumentBuilderFactory.newInstance().getClass()));
   System.out.println(getJaxpImplementationInfo("XPathFactory", XPathFactory.newInstance().getClass()));
   System.out.println(getJaxpImplementationInfo("TransformerFactory", TransformerFactory.newInstance().getClass()));
   System.out.println(getJaxpImplementationInfo("SAXParserFactory", SAXParserFactory.newInstance().getClass()));
   System.out.println(getJaxpImplementationInfo("SchemaFactory", SchemaFactory.newInstance().getClass()));
}
private static String getJaxpImplementationInfo(String componentName, Class componentClass) {
   CodeSource source = componentClass.getProtectionDomain().getCodeSource();
   return MessageFormat.format(
      "{0} implementation: {1} loaded from: {2}",
      componentName,
      componentClass.getName(),
      source == null ? "Java Runtime" : source.getLocation());
}

Possible Solutions

Update your JAXP jar implementation

Do a mvn dependency:tree and see if there are any xerces related jars that need to be removed or updated from an implied version to declaring one that works
Google/Bing the most recent verision of your jar library

Use the default implementation

Given the order used to determine the implementation to load, we can set System property javax.xml.parsers.DocumentBuilderFactory System.setProperty("javax.xml.parsers.DocumentBuilderFactory","com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl");
In command line add -Djavax.xml.parsers.DocumentBuilderFactory=com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl
The best solution for me is passing a parameter to DocumentBuilderFactory to specify which parser to use: DocumentBuilderFactory factory =DocumentBuilderFactory.newInstance("com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl", null);

I hope you find this information useful‎, and if you have aditional information or questions you can leave a comment :)

Abstract Classes, Interfaces and Why Static Abstract Methods can't be declared?

2012-07-02T13:38:00.001-05:00

Lets make a review:
Interfaces

All variables defined in an interface must be public, static, and final.
Interface methods must not be static.
Interface methods implicitly are abstract and cannot have implementations.

Abstract class

Unlike interfaces, abstract classes can contain fields that are not static and final.
abstract classes can contain implemented methods.
An abstract class may have static fields and static methods. You can use these static members with a class reference.
Static methods in abstract classes must be implemented.

Static Methods.

You can call a static method with a class reference or with an object
Static methods can't be overriding.
The calls to static methods are determined by the reference type at compile time, instead of the object type which are determined in run time
Polymorphism aren't supported. You can write a new static method in the subclass that has the same signature as the one in the superclass, thus hiding it.
It is not necessary to have any instance of the class within the static method. The compiler changes the object references for class references when calling static methods.

Given the Java Specification, a method couldn't be Abstract and Static at the same time; You can't declare static methods in interfaces or abstract classes. Nevertheless, you can implement static methods in abstract classes.

The reason to don't allow static and abstract in the same method is that,
You can call a implemented static method, but try to figure out what should happen if you call a not-implemented static method through a class reference ( by an abstract class or interface).

You can't call a static abstract method because you haven't a specific implementation at compile time.

Also you might be thinking in implement this abstract static method in a subclass and make class references to this method through the subclass, but it is not possible given that the static methods doesn't have polymorphic behavior

References:
Interfaces and Inheritance

Static Methods in an Interface

Javascript Variables

2012-06-12T01:29:00.000-05:00

JavaScript is an untyped language. This means that a variable can hold any datatype. It also means that a variable may be assigned data of one particular datatype and then later be given data of a different datatype.

Definition

Variables are used to hold values or expressions. They can be thought of as named containers. You can place data into these containers and then refer to the data simply by naming the container.

Declaring Variables

You declare JavaScript variables with the var keyword

<script type="text/javascript">
var age;
var name;
</script>

After the declaration shown above, the variable is empty.
You can also declare multiple variables with the same var keyword as follows:

<script type="text/javascript">
var age, name;
</script>

When using a variable for the first time it is not necessary to use "var" before the variable name, but it is a good programming practice. Use the var keyword only for declaration or initialization once for the life of any variable name in a document. You should not re-declare same variable twice.

Rules for naming variables

You should not use any of the JavaScript reserved keyword as variable name.
They must begin with a letter (not digit), the underscore character or currency. For example, 123test is an invalid variable name but_123test is a valid one.
JavaScript variable names are case sensitive.
After the first character, can contain letters, digits, and underscores
Cannot contain space

JavaScript Reserved Words:

The following are reserved words in JavaScript. They cannot be used as JavaScript variables, functions, methods, loop labels, or any object names.

abstract
boolean
break
byte
case
catch
char
class
const
continue
debugger
default
delete
do
double
else
enum
export
extends
false
final
finally
float
for
function
goto
if
implements
import
in
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
super
switch
synchronized
this
throw
throws
transient
true
try
typeof
var
void
volatile
while
with

Assignation initialization

Storing a value in a variable is called variable initialization. You can do variable initialization at the time of variable creation or later point in time when you need that variable using the equal (=) sign
If you assign values to variables that have not yet been declared, the variables will automatically be declared as global variables.

<script type="text/javascript">
var name = "Ali";
var age;
age = 2000.50;
</script>

Special variable values

undefined

If a variable hasn't been declared or assigned yet then that variable will be given a special undefined value. Evaluates to false in boolean operations. Always use === when comparing to undefined.
var x;
var y = false;

typeof(x) → undefined (as a string)

x == y → true
x === y → false

NaN

Not a Number, generated when arithmetic operations return invalid results. Evaluates to false in boolean operations. Always use isNaN() when comparing to NaN. NaN is never equal to itself!
var x = 10/seventeen;

x → NaN

var x = 10/seventeen;

x == x → false

Scope

The scope of a variable is the region of your program in which it is defined. JavaScript variable will have only two scopes.
Global Variables: A global variable has global scope which means it is defined everywhere in your JavaScript code.
Local Variables: A local variable will be visible only within a function where it is defined.
JavaScript does not have block scope, so defining variables in blocks can confuse programmers who are experienced with other C family languages. Define all variables at the top of the function.

Hiding variables

Within the body of a function, a local variable takes precedence over a global variable with the same name. If you declare a local variable or function parameter with the same name as a global variable, you effectively hide the global variable.

Local Variables

A variable declared within a JavaScript function becomes LOCAL and can only be accessed within that function.
Function parameters are always local to that function.
You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.
Local variables are deleted as soon as the function is completed.

Global variables

Variables declared outside a function, become GLOBAL, and all scripts and functions on the web page can access it.
Global variables are deleted when you close the page.
If you assign values to variables that have not yet been declared, the variables will automatically be declared as global variables.
Use of global variables should be minimized. Implied global variables should never be used.

Naming Conventions

Names should be formed from the 26 upper and lower case letters (A .. Z, a .. z), the 10 digits (0 .. 9), and _ (underbar).
Avoid use of international characters because they may not read well or be understood everywhere. Do not use $ (dollar sign) or \ (backslash) in names.
Do not use _ (underbar) as the first character of a name. It is sometimes used to indicate privacy, but it does not actually provide privacy.
Most variables and functions should start with a lower case letter.
Global variables should be in all caps.
All variables should be declared before used. JavaScript does not require this, but doing so makes the program easier to read and makes it easier to detect undeclared variables that may become implied global. Implied global variables should never be used.
The var statements should be the first statements in the function body.
It is preferred that each variable be given its own line and comment. They should be listed in alphabetical order.