Work in the constructor anti-pattern

* This post is intended to be a 101 quickie for the less experienced.
* It does not provide new or innovative ways of solving a certain problem,
* just summarizes a topic the way I see it.

This is a topic many have already talked about (a lot), but it still pops up from time to time. Strangely enough, not only in case of junior developers. Continue reading “Work in the constructor anti-pattern”

BigDecimal gotchas

Today I’d like to share some hints on BigDecimals, how and when to use them, what to watch out for and how to avoid strange errors.

When to use them

I think this is the most straightforward of them all. BigDecimals should be used when exact results with arbitrary precision are needed for numerical calculations. Continue reading “BigDecimal gotchas”

Non object-oriented objects

I always feel uncomfortable when I encounter instances of certain classes in the codebase I’m working with. Perhaps uncomfortable is not the right word here; the whole situation is a huge paradox: objects that fail to behave in an object-oriented way. Of course I’m talking about classes like Tuple and Triplet (or whatever name they may have in different libraries). Continue reading “Non object-oriented objects”

POSTing multipart requests with RestTemplate

Some days ago I had to write a little client application to call a RESTful web service; my job was to upload some data, defined in terms of JSON, along with a picture (PNG format, but that does not matter for this time). These tasks are usually carried out with POSTing form/multipart messages to the endpoint – my case was no different, the server was expecting just that. I thought it would be easy and fast to throw in RestTemplate from Spring, but as it turned out, this simple task took me around 12 hours, a complete Sunday and a lot of pain (finally, Sotirios Delimanolis pointed me in the right direction on As it seems, there is little amount of code examples out there, so I thought I’d post one here.

Continue reading “POSTing multipart requests with RestTemplate”

Spring: injecting an enum conditionally

The other day I was working on a piece of legacy code, with old-fashioned xml based Spring injection. All of a sudden I found myself in a situation where I had to inject an enum, based on some condition specified in a .properties file. This is easy to do with Java config, but not so usual to me with XMLs, so I thought I’d put it here. Continue reading “Spring: injecting an enum conditionally”

Book review: Sujoy Acharya – Mockito essentials

A few weeks back I was contacted by Packt Publishing to review a relatively newly published book: Mockito essentials. Without any further talk, let’s see:

I tried to read the book like I had never seen Mockito, or encountered any of the principles of mocking before. Under these conditions some of the chapters were very useful, others less. At many points I had the impression that examples int this book are (maybe) a bit too advanced for beginners, but not so useful for pros. This is mainly because people completely new to mocking/stubbing/faking may get lost in some rather complex pieces of code, while seasoned mockers are reading more advanced books. Continue reading “Book review: Sujoy Acharya – Mockito essentials”

JUnit’s ExpectedException @Rule

Some time ago I had written a post about different ways to deal with exceptions using JUnit. It’s time to augment that post with a truly great way to achieve the same result.

Let’s look at this through an example. The task will be to implement a little method for an insurance company that registers a car to be insured by its license plate number. In Hungary, license plates follow the LLL-DDD pattern, where L stands for an uppercase letter, while D is a digit from 0 to 9. The initial requirement is simple: validate whether the input string conforms to the pattern described above; if it does, save it, else, throw an IllegalArgument exception. Continue reading “JUnit’s ExpectedException @Rule”