ANTLR Hello World! - Arithmetic Expression Parser

Ever wondered how all these programming languages understand what you write? This article reveals the truth: Language Parsing. It is often referred to as parsing, syntax analysis, or syntactic analysis. Regardless of the term, it is the process of analyzing a string of symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal grammar. The following diagram depicts the language parsing process:

As you can see, the Language Parser (which is part of the compiler) takes an input (which is the source code), validates it against the Language Grammar and produces an Abstract Syntax Tree (commonly known as AST which is representing the source code in a tree structure).

ANTLR (ANother Tool for Language Recognition) is a tool to define such grammar and to build a parser automatically using that grammar. It also provides two high-level design patterns to analyze the AST: Visitor and Listener. ANTLR is being used by several languages and frameworks including Ballerina, Siddhi, and Presto SQL. This article introduces ANTLR to you using a hello world application to evaluate basic mathematical expressions as a string.

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Javalin: A Tiny but Mighty Framework

Two years ago, I wrote an article Microservices in a minute using the open source framework MSF4J. Today I came across another framework Javalin: another lightweight framework to develop lightweight web applications with less or no effort. We already have plenty of web frameworks including the shining star Spring. What makes Javalin different is its simplicity. In addition, it can be used as a microservice framework or a tiny web framework to serve a web application with static files. In Javalin developers' words:

Javalin’s main goals are simplicity, a great developer experience, and first-class interoperability between Kotlin and Java.

Comparing Javalin with Spring is like comparing a shaving blade with a Wenger 16999 Swiss Army Knife Giant, but it does what it is supposed to do. If you want to quickly add a REST endpoint for a quick demo or if you just need a simple web framework without any additional gimmicks like Dependency Injection or Object Relational Mapping, consider Javalin. It is easy to learn and lighter to run.

In this article, you will see how to use Javalin as a web framework to serve a contact-us page and how to build a CRUD micro-service using Javalin.

Requirements:

• Java Development Kit 1.8 or the latest
• Apache Maven 3.x
• IntelliJ Idea or any other IDEs

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Serve TensorFlow Models in Java

TensorFlow is a famous machine learning framework from Google and a must to know asset for machine learning engineers. Even though Python is recommended to build TensorFlow models, Google offers Java API to use TensorFlow in Java. Still, Python is the easiest language to build TensorFlow models, even for Java developers (learn Python, my friend). However, enterprise applications developed in Java may require the artificial intelligence offered by a trained TensorFlow model. In this article, you will learn how to load and use a simple TensorFlow model exported from Python.

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Spark 06: Broadcast Variables

If you read the Spark 04: Key-Value RDD and Average Movie Ratings article, you might wonder what to do with popular movie IDs printed at the end. A data analyst cannot ask his/her users to manually check those IDs in a CSV file to find the movie name. In this article, you will learn how to map those movie IDs to movie names using Apache Spark's variable broadcasting.

Suppose you want to share a read-only data that can fit into memory with every worker in your Spark cluster, broadcast that data. The broadcasted variable will be distributed only once and cached in every worker node so that it can be reused any number of times. More about broadcasting will be covered later in this article after the code example.

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Spark 05: List Action Movies with Spark flatMap

Welcome to the fifth article in the series of Apache Spark tutorials. In this article, you will learn the application of flatMap transform operation. After the introduction to flatMap operation, a sample Spark application is developed to list all action movies from the MovieLens dataset.

In the previous articles, we have used the map transform operation which transforms an entity into another entity where the transformation is one-to-one. For example, suppose you have a String RDD named lines, applying lines.map(x => x.toUpperCase) operation creates a new String RDD with the same number of records but with uppercase string literals as shown below:

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Spark 04: Key-Value RDD and Average Movie Ratings

In the first article of this series: Spark 01: Movie Rating Counter, we created three RDDs (data, filteredData and ratingData) each contains a singular datatype. For example, data and filteredData were String RDDs and the ratingRDD was a Float RDD. However, it is common to use an RDD which can store complex datatypes especially Key-Value pairs depending on the requirement. In this article, we will use a Key-Value RDD to calculate the average rating of each movie in our MoviLens dataset.  Those who don't have the MovieLens dataset, please visit the Spark 01: Movie Rating Counter article to setup your environment.

As you already know, the ratings.csv file has the fields movieId and rating. A given movie may get different ratings from different users. To get the average ratings of each movie, we need to add all ratings of each movie individually and divide the sum by the number of ratings.

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Spark 03: Understanding Resilient Distributed Dataset

You are not qualified as an Apache Spark developer until you know what is a Resilient Distributed Dataset (RDD). It is the fundamental technique to represent data in the Spark memory. There are advanced data representation techniques like DataFrame built on top of RDD. However, it is always better to start with the most basic dataset: RDD. RDD is nothing other than a data structure with some special properties or features.

We all know that Apache Spark is a distributed general-purpose cluster-computing framework. There are some common problems faced in a distributed environment including but not limited to:

1. Remote access of data is expensive
2. High chance of failure
3. Runtime errors are expensive and hard to track
4. Wasting computing power is way too expensive

RDD is designed to address the abovementioned problems. In the following section, you will see the properties of RDD and how it solves these problems.

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Spark 01: Movie Rating Counter

Apache Spark is a must to know framework for big data developers. This is an attempt to write a series of articles on Apache Spark to train you from zero to hero. In this series of articles, I will use the latest Apache Spark release which is 2.4.0 as of 2019 January. In the first few articles, we will code and test Apache Spark on IntelliJ Idea. As you may already know, Apache Spark is developed using Scala and of course, there are APIs available for other languages including Java and Python. Still, Scala has preferred over other languages for its performance and compact code. Therefore, you need to prepare the environment first.

My articles will be based on Frank Kane's course on Udemy: Apache Spark 2 with Scala - Hands On with Big Data! I highly recommend his tutorial if you prefer for a video tutorial.

Setup the Environment

Apache Spark 2.4.0 depends on Scala 2.12 which in turn depends on Java 1.8. Scala is unlike Java not very version compatible language. Therefore, please take special care on choosing versions.

Step 1:

Install Oracle Java Development Kit 1.8 on your system. Linux users can follow this article: Install Oracle JDK 8 on Linux

Step 2:

Install the latest IntelliJ IDEA. Again, Linux users can follow my article: Install IntelliJ IDEA on Linux

Step 3:
Install Scala plugin in IntelliJ IDEA. Regardless of your operating system, you can follow the article Setup Scala on IntelliJ IDEA.

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Deploy and Upgrade Android Database From External Directory

After seeing the huge response for the Import and Use External Database in Android article, I have realized the importance of deploying Android database from external sources. The library used in the above article allows you to import database only from the assets directory. However, recently one of my readers, asked for a way to import and upgrade the database from SD card. As a solution for his use case, I have developed a new library named "externalsqliteimporter" which allows you to import database either from assets directory or from SD card. This article explains the application of this Android library using a sample application.

The ExternalSQLiteImporter library allows you to build your SQLite database on your desktop computer, and to import and use it in your Android application. This library has two separate ways to maintain your database.

This library is still under development. Deploying and upgrading  the database from an external directory is not secure as it is publicly available for third party applications as well. Use that feature with caution. 

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RESTful CRUD With Java and MySQL in Minutes

I keep receiving so many requests for an article on how to access MySQL database from Android application. Even though Android applications can have direct access to MySQL database server, that is not preferred due to security issues and high complexity. The easy and best solution is developing a REST web service to receive the requests from whatever the client (including Android applications) and execute them on the database connected with the web service.

There are so many articles already available on the Internet about how to create a web service to perform Create, Read, Update & Delete (CRUD) operations on a database and how to connect from an Android client. However, I wondered why most of them are using PHP to develop the web service! I believe developers find PHP a less painful language to develop web services than Java. In this article, I am going to show how to develop a RESTful CRUD Web service with Java in minutes. As a matured language Java has enough frameworks to make your task easy. I guarantee that you will never look back for a different language once you know the tools.

Prerequisite:

• Eclipse IDE for Java EE or any Java IDE with Apache Maven support. (I recommend IntelliJ IDEA)
• MySQL 5.x
• PhpMyAdmin or any other clients to access MySQL database
• Postman or any other REST Clients

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Inject Views on Android

Have you ever get irritated by the unlimited number of findViewById method calls and complex on-click-listeners? Obviously, they increase the complexity of the code and they consume more time as well. Butter Knife is a perfect solution to get out of these irritating and time-consuming code segments.

Butter Knife is an injection library used to inject views into Java classes. Using this library is not going to reduce the performance since it uses compile-time injection instead of runtime injection. Compared to some other Android libraries and frameworks, it is less featured but personally, I like this library a lot for its less configuration and high performance. This article introduces the basic functionalities of Butter Knife and more details can be found at the official website.

Let's create a simple application with a TextBox and a Button to demonstrate the application of Butter Knife.

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Stripes - Hello, World!

Stripes is an open source web application framework used to simplify Java web development. Stripes provides both View and Controllers of MVC architecture and let the developers port their Model into the system. Comparing to Struts, Stripes is a lightweight and less configuration needed framework, but it provides almost everything provided by Struts. More details about Stripes can be found here.

This tutorial shows you; how to develop a simple web application using Stripes framework in Eclipse.

Prerequisite:

• Java Development Kit 1.5 or latest
• Eclipse JEE
• Apache Tomcat (To add Apache Tomcat to Eclipse, follow this link.)
• Stripes libraries and other dependencies
• Basic knowledge in Java Servlets and JSP.

Create a new Dynamic Web Project

Step 1:

In Eclipse goto File → New → Project… and select Dynamic Web Project

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