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"Java & Agile" was renamed "Python & Machine Learning"

I have started blogging since 2014. In fact, I just happened to know a very nice free blogging course of John Sonmez. Time flies!

I currently work at a startup to build an AI chatbot. It was where Python and Machine Learning become my most focus from now on. That also was a reason why I wanted to rename my blog theme. I still keep using Java in my projects though.

Thank you all for reading my blog so far. It motivates a lot to keep me carrying on this habit.

TL;DR
A new topic "Python & Machine Learning" is added to my blog theme today. Yay!

Creating a Chatbot with RiveScript in Java

Motivation"Artificial Intelligence (AI) is considered a major innovation that could disrupt many things. Some people even compare it to the Internet. A large investor firm predicted that some AI startups could become the next Apple, Google or Amazon within five years"
- Prof. John Vu, Carnegie Mellon University.

Using chatbots to support our daily tasks is super useful and interesting. In fact, "Jenkins CI, Jira Cloud, and Bitbucket" have been becoming must-have apps in Slack of my team these days.

There are some existing approaches for chatbots including pattern matching, algorithms, and neutral networks. RiveScript is a scripting language using "pattern matching" as a simple and powerful approach for building up a Chabot.
Architecture Actually, it was flexible to choose a programming language for the used Rivescript interpreter like Java, Go, Javascript, Python, and Perl. I went with Java.


Used Technologies and ToolsOracle JDK 1.8.0_151Apache Maven 3.5…

A Case Study of Custom JSF Converters - Automatically Converting Years With 2 Digits Into 4 Digits

You can find the demonstrated code of this post on my Github repo here.
The user story" As a banker, I want to enter a client's birthday like 01.01.80 or 01.01.1980,
So that the birthday can be displayed as 01.01.1980 "
Implementation Firstly, I thought about how to use a built-in converter likes the following.

<h:inputText id="birthdate" value="#{data.birthdate}" type="date" > <f:convertDateTime/> <f:ajax event="change" listener="#{data.onCalculate}" execute="@this" render="@this" /> </h:inputText>
However, without defining a pattern, JSF used its default one which was not my desire. It threw an exception when I tried to enter a date like "01.01.90".

> myform:birthdate: '01.01.90' could not be understood as a date. Example: Mar 4, 2018 

Actually, I even could not define either pattern "dd.MM.yyyy" or "dd.MM.yy" for "…

4 Remarkable Notes for JSF Apps Using HTML5

In the previous post, I've already shared with you how my team consults clients by using a HTML prototype. This post is about the used technologies for reusing the provided HTML template and communicating with backend.
What is the issue when using HTML elements with Primefaces components? Primefaces is a great extension for developing JSF web apps. However, it is really frustrating in case we have to make it work with an existing HTML template. Why?
- Primefaces has its own theme for styling.
- Primefaces changes the HTML structure.
Therefore, that would be a huge effort to use the Primefaces' components to replicate the elements of the HTML template; especially it is impossible for images drawing by "canvas" tag.

That requires us to find a better approach. Since Java EE 7 (introducing JSF 2.2 included), it supports to use HTML5 elements. The idea is that JSF components don't effect the style and HTML structure, so we can easily reuse the provided HTML template.…

Java 8 - Persistent data structure

The following is a series of posts about "functional programming in Java" which is the result of my understanding by reading the book "Java 8 in Action: Lambdas, Streams, and Functional-style Programming, by Alan Mycroft and Mario Fusco".
1. Why functional programming?
2. Functional programming in Java 8
3. Java 8 - Using Functions as Values
4. Java 8 - Persistent data structure
Persistent data structure is also known as a simple technique but it's very important. Its other names are functional data structure and immutable data structure.
Why is it "persistent"? Their values persist and are isolated from changes happening elsewhere. That's it!
This technique is described as below:

If you need a data structure to represent the result of a computation, you should make a new one and not mutable an existing data structure.

Destructive updates version
public static A doSomething(A a){ a.setProp1("new value"); return a; }
Functional versi…

JSF, Primefaces - Invoking Application Code Even When Validation Failed

A use case I have a form which has requirements as follow:
- There are some mandatory fields.
- Validation is triggered when changing value on each field.
- A button "Next" is enable only when all fields are entered. It turns to disabled if any field is empty.
My first approach I defined a variable "isDisableNext" at a backend bean "Controller" for dynamically disabling/enabling the "Next" button by performing event "onValueChange", but, it had a problem:
<h:form id="personForm"> <p:outputLabel value="First Name" for="firstName"/> <p:inputText id="firstName" value="#{person.firstName}" required="true"> <p:ajax event="change" listener="#{controller.onValueChange}" update="nextButton"/> </p:inputText> <p:outputLabel value="Last Name" for="lastName"/> <p:inputText …

Java 8 - Using Functions as Values

The following is a series of posts about "functional programming in Java" which is the result of my understanding by reading the book "Java 8 in Action: Lambdas, Streams, and Functional-style Programming, by Alan Mycroft and Mario Fusco".
1. Why functional programming?
2. Functional programming in Java 8
3. Java 8 - Using Functions as Values
4. Java 8 - Persistent data structure
In general, the phrase "functional-style programming" means the behavior of functions should be like that of mathematical-style functions - no side effects.

In programmers' point of views, functions may be used like other values: passed as arguments, returned as result, and stored in data structures. That means we can use the :: operator to create a method reference, and lambda expressions to directly express function values. For example:
//method reference Function<String, Integer> strToInt = Integer::parseInt; //lambda expression Comparator<Integer> comparator =…

Functional programming in Java 8

In my previous post, we discussed about why we should consider to use functional programming. Now, let's delve into what functional programming in Java is.
What is pure functional programming?Shortly, functional programming is programming using functions. A function corresponds to a mathematical function such as log, sin. Basically, it takes zero or more arguments, give one or more result, and has no side effects.
We can't completely program in pure functional style in Java Why?  For example, calling Scanner.nextLine twice typically gives different result.

So, it's just called "functional-style programming". How is that?
- There is no mutating structures visible to callers. That means your side effect may not be visible to a program, but it's visible to the programmer in terms of slower execution.
- A function or method shouldn't throw any exceptions (follows the concept "pass arguments, return result"). We can use types like Optional<T> i…

Small Changes to Java 7 via Project Coin and Why They are Useful

Did you know how new features were added into Java 7? The following are functionalities that can be considered.
Source: [1] Project Coin is all about the changes in the range from syntactic sugar to new language feature. This is what we're talking about today.

Since Java 7 is the first version developed in an open source manner, there is an amount of actions that must be performed for any changes as follows:
Update the Java Language Specification (JSL)Implement a prototype in the source compilerAdd library support essential for the changeWrite tests and examplesUpdate documentEtc, ... Project Coin has submitted a lot of proposals (almost 70) but only some of them are chosen to Java 7. Why? Briefly, Java is a rich static type system and it has a lot of possible interaction points between different bits of it. Making changes to this type system is prone to creating unexpected surprises.

Wow! It is tough, right? Let's take a look what features Project Coin brought to Java 7.
Strings…

Using Drools to Dynamically Manipulate Metadata of JSF Components

The post is just an approach to change metadata (e.g maxlength, required, etc) of JSF components (e.g. inputText, selectOneMenue, etc) by Drools.
Project structure Tools being usedJava version 1.8.0_131Apache Maven 3.5.0Apache Tomcat 8.0.16 Don't forget to configure your confidential information on  these following files: pom.xml, settings.xml (Maven) and tomcat-users.xml (Tomcat).
For example:
Source codehttps://github.com/vnnvanhuong/java_lab/tree/master/jsfdrools

Building an App for Removing Multiple Slack's Files

You're a developer. What do you do in your spare time? One of my most excited task for sharpening my skills is starting build a pet project. MotivationSlack is cool! It's free. It supports for team collaboration very well.

However, my team only has storage limits due to a free account. We got a warning message as below:
Your file was uploaded — it’s safe and sound in Slack. Unfortunately your team doesn’t have any storage space left. To get more space, you can upgrade to a paid account or delete some of your older files. Since my team plan of upgrading to a paid account is still up in the air, I intended to go with "deleting some of our older files" first. (But we will, Slack. You are great!) Play Around I got started by googling keyword "remove slack files". Here it is:
https://get.slack.help/hc/en-us/articles/218159688-Delete-shared-files

Uh huh! But I only could delete one file at a time.
We're afraid it's not possible to bulk delete files. We kn…

Why Functional Programming Matter

What issues do we concern when implementing and maintaining systems? One of the most concern is debugging during maintenance: "this code crashed because it observed some unexpected value."

Then, it turns out that the ideas of no side effects and immutability, which functional programming promotes, can help.
Shared mutable data is the root cause Shared mutable data are read and updated by more than one of the methods. Share mutable data structures make it harder to track changes in different parts of your program.

An immutable object is an object that can't change its state after it's instantiated so it can't be affected by the actions of a function. It would be a dream to maintain because we wouldn't have any bad surprises about some object somewhere that unexpectedly modifies a data structure.
A new thinking: Declarative programming There are two ways thinking about implementing a system by writing a program.

- Imperative programming: has instructions that …

Review - The Object-Oriented Thought Process, by Matt Weisfeld

In this post, I would like to point out what I understood after closing my eyes and thinking about what  exactly I have learned from this book. That means the layout of content does not follow the book.
From Procedural to Object Oriented Once upon a time, there is an issue that it is very hard to test and debug in Procedural programming because the data is sometimes global and can be modified by multiple functions.

Object-Oriented (OO) programming addresses these problems by combining both data and functions into an object. That means only functions belong to the object can access its own data.

Let us check the below two different approaches for a case that we want to transfer information between clients and servers across a network.

-    Procedural programming: a client (browser) transfers a JSON data to a server which needs to know how to process with this data. In order words, a handshaking agreement must be defined for the client and server in order to work together.
-    OO prog…

Building a Wizard with Chain of Responsibility Pattern

What is the Idea? We want to create a page that there are some steps and each step has its own business. Users are able to click on a step and its status could be changed. Primefaces owns a component "Wizard" but it it quite hard for us in order to apply our very specific and complicated business domain logic on each step; even we cannot click on a step of this component.

We somehow are able to use the component "TabView" works with a strong back-end mechanism. A backend mechanism! what do I mean? Yes, we need it because we want to abstract the behaviors of each step otherwise we will get trouble with many events handling. Obviously, each step has some behaviors  such as "next", "back" and "switch' are the same and they are related to each other; but the business of these behaviors can be different totally. That is where the pattern "Chain of Responsibility" can be applied.
Step by Step Building It! In this simple project, I …

Attribute 'for' of label component with id xxxx is not defined

I got the warning in the log file when I have used the tag <h:outputLabel> without attribute "for" in xhtml file. It was really polluting my server log files.

The logged information actually makes sense anyway! We could find an answer as the following:

"Having h:outputLabel without a "for" attribute is meaningless. If you are not attaching the label, you should be using h:outputText instead of h:outputLabel."

However, these solutions are not possible just for my situation. Instead of using h:outputText for only displaying text, my team has used h:outputLabel too many places. We were nearly in our release time (next day) so it is quite risky and takes much efforts if we try to correct it. Because the style (with CSS) is already done with h:ouputLabel. The alternative by adding attribute "for" the existing h:outputLabel is not reasonable either. I really need to find another solution.
Fortunately, I came across a way if I change to use p:out…

Meaningful Names - Code Review Checklist with Example

"Names are everywhere in software". "The hardest thing about choosing good names is that it requires good descriptive skills"[1]. In my previous post, I emphasized that we should take care our code, so now let's start with naming.

Issue Original code Revised code Reveals nothing int d; //elapsed time in days int elapsedTimeInDays; Difficult to understand public List<Cell> getThem()
public List<Cell> getFlaggedCells()
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