development

7 posts

Spring Data MongoDB MappingInstantiationException

Polymorphic fields with MongoDB and Spring Data

Depending on your needs using polymorphism might benefit different aspects of the project. For example, having a limited class hierarchy might make your code cleaner and more expressive in contrast to a single class having nullable fields or a type label. And it only seems natural to use it with document-oriented databases like MongoDB. But if you want to have a document with polymorphic fields using MongoDB and Spring Data you might face an exception similar to this: MappingInstantiationException: Failed to instantiate ...FieldType using constructor NO_CONSTRUCTOR with arguments. Let’s see why this happens and how to fix that issue properly.

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reduce Java docker image size

How to reduce Java docker image size

If you’ve been using Java for a while, you might have noticed that starting with Java 11, Java Runtime Environment (JRE) doesn’t have a separate distribution anymore, it is only distributed as a part of Java Development Kit (JDK). As a result of this change, many official Docker images don’t offer a JRE-only image, e.g.: official openjdk images, Amazon corretto images. In my case using such an image was resulting in an app image of 414MB, where the app itself was only taking around 60MB. What a waste of space!

But fear not, as I’m going to show you how to reduce Java docker image size dramatically.

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Using Liquibase with Kubernetes

Using Liquibase with Kubernetes

If you’re using Liquibase for database versioning with Kubernetes to deploy your app, you might have faced an issue when a migration gets stuck because Liquibase can’t acquire lock. It might look somewhat like this:

liquibase.exception.LockException: Could not acquire change log lock. Currently locked by LockOwner ... at liquibase.lockservice.StandardLockService.waitForLock(StandardLockService.java:236) at liquibase.Liquibase.update(Liquibase.java:184) at liquibase.Liquibase.update(Liquibase.java:179)
Code language: Properties (properties)
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How to unblock yourself

How to unblock yourself

It’s not uncommon for a software engineer to find themself blocked. The reasons might vary: it could be a high uncertainty, when it’s unclear how exactly to implement the feature; or it could be a tech decision to take having multiple options with their own pros and cons. With this article I want to share the way I take decisions in such cases and how it might help you to unblock yourself.

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