Huseyin ABANOZ

Introduction Use of volatile variables is common among Java developers as a way of implicit synchronization. JIT compilers may reorder program execution to increase performance. Java memory model[1] constraints reordering of volatile variables. Thus volatile variable access should has a cost which is different than a non-volatile variable access. This article will not discuss technical details on use of volatile variables. Performance impact of volatile variables is explored by using a test application. Objective Exploring volatile variable costs and comparing with alternative approaches. Audience This article is written for developers who seek to have a view about cost of volatile variables. Test Configuration Test application runs read and write actions on java variables. A non volatile primitive integer, a volatile primitive integer and an AtomicInteger is tested. Non-volatile primitive integer access is controlled with ReentrantLock and ReentrantReadWriteLock  to compa

Introduction Obfuscation is the act of reorganizing bytecode such that it becomes hard to decompile. Many developers rely on obfuscation to save their sensitive code from undesired eyes. Publishing jars without obfuscation may hinder competitiveness because rivals may take advantage of easily decompilable nature of java binaries. Objective Spring Boot applications make use of public interfaces, annotations which makes applications harder to obfuscate. Additionally, maven Spring Boot plugin creates a fat jar which contains all dependent jars. It is not viable to obfuscate the whole fat jar. Thus obfuscating Spring Boot applications is different than obfuscating regular java applications and requires a suitable strategy. Audience Those who use Spring Boot and Maven and wish to obfuscate their application using Proguard are the target audience for this article. Sample Application As the sample application, I will use elastic search synch application from my GitHub repository.

Problem I want my previously written java application to be run multiple times by a shell script with calculated parameters. However, target platforms may not contain bash. Thus I decied to write another class which acts like a bash script file and launch my application with generated parameters. My application has static variables and static classes. Before every launch I want the state information be cleared. But since I work in the same JVM, static objects will not be removed. It comes out using static fileds and initializers may not be a good approach. There should be a way to solve this.  The solution is to use a custom classloader. Classloader will load all classes. At the end of the execution, the classloader and all the classes loaded will be garbage collected. At next execution, all classes will be reloaded. Solution : Custom Class Loader Class loaders can be considered a container to launch an application. Servlet containers like Tomcat uses a custom classloade

Assume you have large amount of text data and want to do search on your data. You decided to use elasticsearch or solr as search engine. Spring Data is your friend. This document shows an example application that uses elasticsearch with spring data. This application uses elasticsearch and JPA at the same time. Data comes from mysql and goes to elasticsearch. Create document class to represent your domain object. Next thing you need is repository class to manage your domain object. Query methods are possible. Now we can work store data to elasticsearch using repository object. For JPA entity and repository classes see [1]. Component annotation makes this class spring managed. Autowired annotation tells spring to create required repository objects. Transactional annotation is required for declarative transaction management. Now spring boot application entry point comes. EnableElasticsearchRepositories is need to activate elasticsearch repository. Since another repository is

Spring framework comes with many modules that makes java developers' life easier. Spring Boot works like a charm. It has never been easier to write java applications. This document is created to show how simple a JPA application can be written. A JPA application starts with creating JPA entity and DAO classes. JPA entity classes can be generated using a tool that comes with any Java IDE. In spring data, DAO classes are called as Repository classes. A repository or DAO object is used to save,update,delete or retrieve entity objects. Traditionally DAO classes were created using Base Dao classes. Base classes were saving us from writing boiler plates for save, update or delete methods. But when it comes to retrieval methods, boiler plate codes were unavoidable. Good news is that, spring data comes with a good idea. Query methods save us from boiler plates. See [1] for more details. Entity class is a standard JPA entity. An example service class is given below. By use of A

Warning!  This article is not up-to-date anymore and might be inaccurate. Please refer to following post. http://huseyinabanozeng.blogspot.com/2018/07/obfuscating-spring-boot-projects-using.html This article is an extension to article named  Multi Module Maven Project Using Assembly Plugin . Assembly module is added with obfuscation configuration. Obfuscation is a technique to make byte code harder to reverse engineer to protect source code. In Java word there are not many freeware obfuscation tools. One of the well known obfuscation tools is named proguard. It has a nice maven plugin. But I could not make proguard-base 4.10 work. It gave ClassNotFoundErrors due to worngly obfuscated class names. Another option is yguard from  yworks . Yguard has an ant task and works with maven ant-run plugin as well. My experience with yguard is pretty well, it works just fine. Below is the pom file for assembly module with obfuscation configuration. <? xml   version = &q

  Maven is a very flexible and powerful technology. Anyone in Java software industry is suggested to make use of it. This document will describe multi module maven project. Assembly plugin is used to merge outputs of modules into one jar. Provided project is a full fledged Java project which uses spring framework for dependency injection, hibernate for ORM. The project comes with several basic classes to make use of the project architecture and show use of some usefull patterns. All project files are attached to the end of this document. 1.        Parent Pom Lists all submodules and uses maven-assembly-module. <? xml   version = "1.0"   encoding = "UTF-8"   standalone = "no" ?> <project   xmlns = " http://maven.apache.org/POM/4.0.0 "   xmlns:xsi = " http://www.w3.org/2001/XMLSchema-instance "           xsi:schemaLocation = " http://maven.apache.org/POM/4.0.0   http://maven.apache.org/maven-v4_0_0.