Briefly about me
At the moment (from June 2025) I am a ‘freelance’ programmer and, as part of my business activity (JDG), I carry out tasks related to maintaining, expanding and creating web services, mainly using Java and Python (plus ‘frontend’ solutions).
I program mainly in Java and I have this skill confirmed by a valued certificate Oracle Certified Professional: Java SE 17 Developer
In addition to the current experience within sole proprietorship I have two years of experience as a Junior Software Developer in a ‘fintech’ company. In addition, I have several years of non-commercial experience in creating utility tools (also implemented on servers), which, for example, have supported my work and the work of others in the production plant in the past. I have “Technical and IT” studies (master) and Postgraduate studies in Programming in Java more
Technologies I work with
- Java;
- Kotlin;
- JavaScript / TypeScript;
- Python;
- PHP (basic);
- HTML, CSS;
- SQL;
Frameworks, interfaces and standards:
- Spring Framework;
- JakartaEE;
- JDBC, JPA, Hibernate, CRUD;
- Angular, AngularJS, React;
- MySQL, PostgreSQL, MongoDB;
- JUnit, Spock, Mockito;
- Docker;
- Jenkins
Skills
- Intermediate knowledge of Java and Kotlin and experience in developing applications in these languages;
- Ability to work with HTML, CSS, JavaScript as well as the Angular and AngularJS frameworks and experience in developing services with Angular;
- Basic knowledge of other languages, such as Python, PHP;
- Knowledge and experience with relational databases and SQL, and to a lesser extent with non-relational databases;
- Basic knowledge of version control and continuous integration and delivery tools (CI/CD) (GIT, Jenkins, Docker);
- Experience and ability to cooperate in a team of programmers using version control systems;
- Experience of working in Agile methodologies (Jira, Confluence).
Practical skills
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Working in the appropriate development environment (such as IntelliJ, PyCharm, SpringToolSuite, AndroidStudio or VisualStudioCode), choosing the right dependencies and the ability to create a project in Java, Kotlin, Python or JavaScript (traditional or web applications, also for Android systems);
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Creating a database that will cooperate with the project: establishing a connection with the database, using object-relational mapping technology in communication between the application logic and the database;
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Creating an application view layer, using JPA technology (JakartaServerPages) or templates (like Thymeleaf). Also working with a more advanced solution using the AngularJS framework (a separate application);
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Ability to write tests for the created application and ensure proper validation of data processed by the application (JUnit, Mockito, Spock);
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Ability to implement the authorization process in the created application (also using a database);
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Installation of the necessary software on the server and deployment of the application to the server under the Debian system (including domain assignment);
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Using version control tools such as GIT (GitHub, Bitbucket) for collaboration with others and for continuous software delivery (Jenkins);
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Ability to create a web project in Python, e.g. in the PyCharm environment;
My Projects
Quiz-Master
This is currently a project still under development (with basic functionality)
Technological characteristics:
> Java, Spring, Angular,
> MongoDB, Liquibase,
> Groovy, Spock, JUnit
The application that allows learning and testing by completing quizzes, for example, related to Java programming or, ultimately, any other topic. Sample quizzes related to Java learning are currently available. There’s no need to log in to the service to take a quiz. The test time and score are recorded. After completing the test, you can review your results and validate all questions. Basic quiz management options are now available, such as creating new quizzes and adding questions from an existing set.
Operation
The application displays a list of available quizzes. After selecting a quiz (and optionally providing a name and email address), click ‘start quiz’ (questions with answers will load and the quiz will begin). After selecting an answer, the quiz is sent to the backend, and the score is returned. The score includes a grade (pass/fail), the number of correct answers, a percentage score, and the answer time (calculated from the click on the selected quiz in the backend based on the generated ‘session ID’).
Along with the score, explanations for the questions and correct answers are returned. This allows the frontend to change the color scheme after a quiz is completed, correct/incorrect answers in the form (and entire questions depending on the grade).
You can create your own quizzes from existing questions.
Technologies
- The ‘backend’ part of the application was written in Java using the Spring framework;
- The ‘frontend’ was created using the Angular framework (also using Bootstrap in view);
- It uses the MongoDB non-relational database and the Liquibase tool for migration;
- When writing tests, apart form Java and JUnit, the Groovy language and the Spock and RestAssured libraries were used;
Application Features
- The concept of conducting various types of tests/quizzes using the ‘backend’ and database allows for:
- ensuring high quality results, because the data sent with questions to the ‘frontend’ does not contain results and the possibilities of manipulating the test execution time are limited because the time is counted in the ‘backend’;
- adding quizzes and expanding them;
- registering results;
- each time ‘mixing’ the order of questions and answers within a question;
- editing parameters, such as the test pass rate.
Planned Functionalities
- User registration and login;
- Quiz statistics and results summaries;
- Extensive quiz addition and editing capabilities;
- Ability to comment on questions;
- Results sent to email
Links
My-Books
This application offers simple functionality, yet with potential for development. In its current form, it allows users to search and add books available via the GoogleBooks API to their collection. Added items can then be edited, deleted, or marked as read.
Technologies
- The backend application is written in Java using the Spring framework;
- It uses the PostgreSQL relational database;
- The frontend layer uses the React framework.
- Other technologies: Liquibase, Docker, Gradle, JWT
Features
- User login and registration;
- Search for books available in Google Books;
- Results pagination;
- Adding books to your book list;
- Ability to view, delete, and mark books as read;
Links
J-Countant
The application helpful in managing finances in a small business (a modified version of the application originally written in Python, using other technologies). The tool consists of two separate applications (‘frontend’ and ‘backend’ are defined separately).
After entering data on actual transactions carried out in the business, the tool allows you to determine the profit, the tax base and the amount of taxes necessary to pay (depending on the type of taxation).
Characteristics
Application written in the REST architecture, working on data stored in the PostgreSQL database. The ‘back-end’ part has now been implemented along with the database in Docker containers on a VPS server under Debian. The ‘front-end’ part, communicating with the ‘back-end’ part, was placed in a different location using a service offered by Amazon Web Services (AWS).
Technologies
- ‘Backend’ part of the application written in Java using the Spring framework;
- Uses a relational database PostgreSQL;
- Used Spring components: Spring Security, Spring Web, Spring Data;
- Other technologies: JPA, Hibernate, Liquibase, Hibernate Validator;
- Tools used in application testing: JUnit, Mockito, AssertJ, Testcontainers;
- Technologies used to deploy the application: Git, Docker, Docker Compose, AWS;
- The ‘frontend’ part implemented with AngularJS framework
Functionalities
- Login and new user registration;
- Adding and deleting receipts/invoices, and then approving transactions based on them (outgoing or incoming);
- Ability to define a special transaction, such as tax payment or salary payment;
- Balance calculation:
- state of finances;
- gross income;
- costs;
- net balance;
- VAT;
- income tax to pay;
- profit depends on the method of taxation;
- paid taxes, remaining tax to pay;
- paid profit
- Insight into recent transactions, search for invoices and transactions;
- Generate calculations for a selected date range;
- Calculations for the current or previous month
Links
Quality Troubles Database
An application supporting a database of quality problems (typical defects and procedures for improvement) occurring in a specialized plant producing plastic bottles.
Technologies
- Application written in Java using the Spring framework;
- Uses MySQL relational database;
- View layer developed with AngularJS
Functionalities
- The ability to easily browse and search for available quality problems in the database and view the typical causes of a given problem and its proposed solutions;
- Registration and login service implemented;
- The ability to enter your own causes and solutions to a given problem to the logged-in user;
Lins
Utility Recorder
A desktop tool helpful in monitoring the consumption of utilities, such as water or electricity (it can also be used to record other things). It saves the data to a file, reads it into a table and calculates consumption between records, totals and averages. The data is presented in a simple graph.
Technologies
- Application written in Java;
- Standard libraries for window applications like Swing were used
Functionalities
- Creating a new record, adding table entries, editing data;
- Calculation of consumption, average and preview of data on the diagram;
- Permanent recording of data in a file;
- Ability to edit data from the file level
Linki
Py-Countant
The application helpful in managing finances in a small business. After entering data on actual transactions carried out in the business, the tool allows you to determine the profit, the tax base and the amount of taxes necessary to pay (depending on the type of taxation).
Technologies
- Application written in Python using FastAPI technology;
- Uses SQLite relational database;
- Other technologies: SQLAlchemy, Pydantic, Jinja2
Functionalities
- Login and new user registration;
- Adding and deleting receipts/invoices, and then approving transactions based on them (outgoing or incoming);
- Ability to define a special transaction, such as tax payment or salary payment;
- Balance calculation:
- state of finances;
- gross income;
- costs;
- net balance;
- VAT;
- income tax to pay;
- profit depends on the method of taxation;
- paid taxes, remaining tax to pay;
- paid profit
- Insight into recent transactions, search for invoices and transactions;
- Generate calculations for a selected date range;
- Calculations for the current or previous month
Links
Energy balance monitoring application
My final project in Java Application Development. The app is a food/activity diary and provides personal energy balance calculations. The view layer uses templates.
Technologies
- Application written in Java using the Spring framework;
- Uses MySQL relational database;
- In the view layer was used The Thymeleaf template
Functionalities
- Login and registration carried out using a database;
- Possibility of keeping a food/activity diary - adding and deleting entries;
- Database of meals and activities from which you can add items to your diary;
- Ability to expand the base with new meals and activities;
- Calculation of the balance for any range and its evaluation based on the user’s needs;
- Calculation and evaluation of BMI (Body Mass Index);
- Ability to view and edit user data
Links
Puzzle game: Number puzzle
A simple puzzle game where you move blocks to arrange them in a row in the correct order.
Technologies
- Java;
- Basic Java libraries for window applications: Java AWT;
Functionalities
- The blocks automatically mix when the game starts;
- The ability to change the number of blocks (level) and reset the game state;
- The application counts the number of moves made and the time of the game.
Links
More about me
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Born in 1984, residing in Zielona Góra city, Poland.
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In the years 2003 - 2008 I studied: ‘Technical and Information Technology Education’ at the University of Zielona Góra, where, among other things, I acquired basic knowledge of computer science and programming (general computer science, HTML and programming languages - mainly Turbo Pascal) and gained pedagogical preparation for teaching technology and computer science ( IT teaching practices).
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I have many years of experience in production work as production supervision, process setting and machine repair.
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Experience as a CNC operator (as well as the course “Operation and programming of numerically controlled machine tools”).
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A few years ago (before taking up a job in IT) I decided to take an interest in “typical” programming and a more “modern” language (as opposed to Pascal), such as Java, so that in the future I could change the nature of my work to be more independent and universal, not directly related to production work.
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While still working at the production plant, I decided on my own initiative (above and beyond my professional duties) to create the production tools described above, which help some employees supervise production at the plant where I was employed until September 2022.
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Years 2020/2021 Postgraduate studies: Programming Java applications, WSB University in Wrocław.
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Currently, I have two years of experience (Since February 2023 to January 2025) as a Junior Software Developer in a company from the financial industry. The position held had a Java profile, and in practice also involved programming in the Kotlin language, and also included ‘frontend’ work with the Angular framework and several other technologies.
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June 2025: start of business activity (JDG) and execution of orders related to creation, maintenance and expansion of projects mainly in Java and Python languages. The actual scope of my activity includes: backend, frontend and deployment.
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December 2025: Pass the test and earn the coveted Oracle Certified Professional: Java SE 17 Developer certification.
Contact
- gerstel.tomasz@gmail.com
- linkedin.com/in/tgerstel
- github.com