java – Shekhar Gulati

Building a simple JSON processor using Java 17 and GraalVM

This week I finally decided to play with GraalVM to build a simple command-line JSON processor based on JsonPath. I find jq syntax too complex for my taste so I decided to build JSON processor based on JsonPath. Since, I wanted to release this as a native executable GraalVM seemed like a good soluton.

GraalVM is a relatively new JVM and JDK implementation built using Java itself. It supports additional programming languages and execution modes, like ahead-of-time compilation of Java applications for fast startup and low memory footprint.

Writing scripts in Java 11 and beyond

Many Java users hate it at times for being too verbose. Many of us have started using other languages like Kotlin or Scala for their terseness and expressiveness. One of the feature that Java programmers like about these modern languages is their ability to do quick experimentation. There are times you do not want to create a project in your IDE, configure build tool, create package structure and then write the code. There is a lot of yak shaving involved before you can automate that one thing that is nagging you. You just want to write a script and move on.

Before JDK 11, Java language did not give you the means to achieve this. Since Java 11, you can write single source file scripts to automate tasks. You do not have to compile the Java file before executing it. You write your Java file and then directly execute it.

How to create a custom Spring Boot FailureAnalyzer

Today, I was working with a Spring Boot application that does local JVM cache warming on the server start up. Application was calling a global Redis cache and storing state that does not change often in an in-memory JVM cache. It is a common pattern that many applications use. In our case, application not only just warm the cache but it also first process some data and then cache the result in the local JVM cache.

Many times junior developers forget to start redis or any other depending service and then application fails to start on their local machine. Then, they need to spend few minutes reading the long Java stack trace to find the problem. These stack trace can be quite long. And, it is difficult to find needle in this haystack.

Recently, I learnt about a Spring Boot feature called FailureAnalyzer. FailureAnalyzer allows you to intercept exceptions that occur at the start-up of an application causing an application startup failure. Using FailureAnalyzer you can replace the stack trace of the exception with a more human readable message. The best example of this is when your code has cyclic dependencies. A common example of cyclic dependency is a bean A depending on bean B and vice versa as shown below.

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Intersection Types in Java Generics

Today, I was looking at JDK 8 Collections.max function declaration and noticed a weird & in the type declaration. Most normal Java developers will not remember exact function declaration so I am writing it below.

public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll)

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Markov chains in Java: Suggest what Narendra Modi will say using Markov chains

Recently, I read an article[1] on Markov chains. In the post, author showed how we can build autocomplete functionality using them. The article piqued my interest to learn more about Markov chain and I started looking for an example application that I can build using it. I decided to build a web application that will suggest me what Indian prime minister Narendra Modi[2] will say after a word/pair of words/triplet for words.

I am not a supporter of Narendra Modi style of leadership. The reason I chose him is because I could easily find text of all his speeches on the web [3].

This post is divided into three sections:

What is Markov chain?
Create dataset for the application
Build the application that uses Markov chain

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Using Java Flight Recorder to Profile Spring Boot applications

Few months back I had to do performance optimisation of a low latency application. The tool that helped me a lot was Java Flight Recorder. Today, I had to do some similar work and I completely forgot how I was able to launch flight recorder GUI. In this short post, I will show you the process that I followed to create flight recorder recordings.

From the official documentation,

Java Flight Recorder (JFR) is a tool for collecting diagnostic and profiling data about a running Java application. It is integrated into the Java Virtual Machine (JVM) and causes almost no performance overhead, so it can be used even in heavily loaded production environments. When default settings are used, both internal testing and customer feedback indicate that performance impact is less than one percent. For some applications, it can be significantly lower. However, for short-running applications (which are not the kind of applications running in production environments), relative startup and warmup times can be larger, which might impact the performance by more than one percent. JFR collects data about the JVM as well as the Java application running on it.

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Gradle Tips

Over the last few years I have started using Gradle as my primary build tool for JVM based projects. Before using Gradle I was an Apache Maven user. Gradle takes best from both Apache Maven and Apache Ant providing you best of both worlds. Gradle borrows flexibility from Ant and convention over configuration, dependency management and plugins from Maven. Gradle treats task as first class citizen just like Ant.

A Gradle build has three distinct phases – initialization, configuration, and execution. The initialization phase determine which all projects will take part in the build process and create a Project instance for each of the project. During configuration phase, it execute build scripts of all the project that are taking part in build process. Finally, during the execution phase all the tasks configured during the configuration phase are executed.

In this post, I will list down tips that I have learnt over last few years.

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Getting started with Apache Dubbo and Spring Boot

This week I decided to play with Apache Dubbo. I follow Github trending repositories daily and for many weeks and months Apache Dubbo is one of their popular Github Java repository. It has more than 20,000 stars. So, I decided to give it a shot. One of the reasons for Dubbo popularity is that it is created by software engineers at Alibaba. Alibaba is a Chinese multinational conglomerate specializing in e-commerce, retail, Internet, AI and technology.

From its website, Apache Dubbo is

A high-performance, light weight, java based RPC framework. Dubbo offers three key functionalities:

Interface based remote call

Fault tolerance and load balancing

Automatic service registration & discovery

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Introduction to Micronaut – A new JVM framework

Recently, I discovered a new framework in Java land called Micronaut. Being a Java developer for last fourteen years, I have seen many Java frameworks come and go. Apart from Spring, there are very few frameworks that made a mark. After a long time, I discovered a framework that is challenging the status quo of web development in Java.

Micronaut is an open-source modern JVM framework for building modular, easily testable microservice and serverless applications. It is a truly polyglot framework. You can build applications in Java, Kotlin, and Groovy.

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Getting Started with Amazon Corretto: Production Ready Distribution of OpenJDK

In November 2018, James Gosling (who now works at Amazon), father of Java released Corretto at Devoxx Belgium conference. Amazon Corretto is no-cost, multi platform, production ready distribution of OpenJDK. This comes at a time when Oracle announced that it will no longer provide free binary downloads of JDK after a six-month period; and neither it will patch OpenJDK with fixes after that period. The six-month is the new release cycle for new JDK versions. If you follow Java, then you might be aware that Java has moved to six month release cycle. The latest version of JDK is 12.

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