Mocking is an essential part of unit testing, and the Mockito library makes it easy to write clean and intuitive unit tests for your Java code.
Get started with mocking and improve your application tests using our Mockito guide:
Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.
Get started with understanding multi-threaded applications with our Java Concurrency guide:
Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:
Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.
But these can also be overused and fall into some common pitfalls.
To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:
Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:
Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.
I built the security material as two full courses - Core and OAuth, to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project.
You can explore the course here:
Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.
Get started with Spring Data JPA through the guided reference course:
Refactor Java code safely — and automatically — with OpenRewrite.
Refactoring big codebases by hand is slow, risky, and easy to put off. That’s where OpenRewrite comes in. The open-source framework for large-scale, automated code transformations helps teams modernize safely and consistently.
Each month, the creators and maintainers of OpenRewrite at Moderne run live, hands-on training sessions — one for newcomers and one for experienced users. You’ll see how recipes work, how to apply them across projects, and how to modernize code with confidence.
Join the next session, bring your questions, and learn how to automate the kind of work that usually eats your sprint time.
Distributed systems often come with complex challenges such as service-to-service communication, state management, asynchronous messaging, security, and more.
Dapr (Distributed Application Runtime) provides a set of APIs and building blocks to address these challenges, abstracting away infrastructure so we can focus on business logic.
In this tutorial, we'll focus on Dapr's pub/sub API for message brokering. Using its Spring Boot integration, we'll simplify the creation of a loosely coupled, portable, and easily testable pub/sub messaging system:
1. Overview
In this tutorial, we’ll learn how to add borders to an Excel sheet using the Apache POI Java library.
For more basics on excel handling, we can start with working with Microsoft Excel in Java.
2. Excel Borders
We can create borders to an excel cell or for a range of cells. These borderlines can be in a variety of styles. Some example styles include thick lines, thin lines, medium lines, dotted lines. To add more variety, we can have colored borders.
This image shows some of these variety borders:
- Cell B2 is with thick line border
- D2 cell is with a wide violet border
- F2 cell is with a crazy border, each side of the border is with different style and color
- Range B4:F6 is with medium-sized border
- Region B8:F9 is with medium-sized orange border
3. Coding for the Excel Borders
The Apache POI library provides multiple ways to handle borders. One simple way is to refer to cell ranges and apply borders.
3.1. Cell Ranges or Regions
To refer to a range of cells we can use CellRangeAddress class:
CellRangeAddress region = new CellRangeAddress(7, 8, 1, 5);CellRangeAddress constructor takes four parameters first row, last row, first column, and last column. Each row and column index starts with zero. In above code, it refers to cell range B8:F9.
We can also refer to one cell using CellRangeAddress class:
CellRangeAddress region = new CellRangeAddress(1, 1, 5, 5);The above code is referring to the F2 cell.
3.2. Cell Borders
Each border has four sides: Top, Bottom, Left, and Right borders. We have to set each side of the border style separately. BorderStyle class provides a variety of styles.
We can set borders using RangeUtil class:
RegionUtil.setBorderTop(BorderStyle.DASH_DOT, region, sheet);
RegionUtil.setBorderBottom(BorderStyle.DOUBLE, region, sheet);
RegionUtil.setBorderLeft(BorderStyle.DOTTED, region, sheet);
RegionUtil.setBorderRight(BorderStyle.SLANTED_DASH_DOT, region, sheet);
3.3. Border Colors
Border colors also have to be set separately on each side. IndexedColors class provides a range of colors to use.
We can set border colors using RangeUtil class:
RegionUtil.setTopBorderColor(IndexedColors.RED.index, region, sheet);
RegionUtil.setBottomBorderColor(IndexedColors.GREEN.index, region, sheet);
RegionUtil.setLeftBorderColor(IndexedColors.BLUE.index, region, sheet);
RegionUtil.setRightBorderColor(IndexedColors.VIOLET.index, region, sheet);
4. Conclusion
In this short article, we have seen how to generate a variety of cell borders using CellRangeAddress, RegionUtil, BorderStyles, and IndexedColors classes. Each side of the border has to be set separately.
