Parsing dot separated keys to nested YAML objects with SnakeYaml

Learn how to effectively convert dot-separated keys in a HashMap into nested YAML objects using SnakeYaml in Java.
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Parsing Dot Separated Keys to Nested YAML Objects with SnakeYaml

One common challenge developers face when working with data formats like YAML in Java is parsing dot-separated keys into a nested structure. If you've been using SnakeYaml to generate your YAML files and find that your output appears flat despite your expectations, you're not alone. In this post, we will explore how to effectively transform a HashMap with dot-separated keys into a properly nested YAML format.

Understanding the Problem

Let's consider a simple example where you have a HashMap with dot-separated keys:

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When you write this map to a YAML file using SnakeYaml, the result will look like this:

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This output isn't structured as you might expect. Instead of having nested objects, you end up with two flat entries. Our goal is to modify this output so that it appears as:

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This format is easier to read and utilize, particularly when dealing with complex data structures.

Solution Overview

To achieve this transformation, you have a couple of options available depending on whether you have control over the structure of your input map.

Option 1: Direct Construction of Nested Maps

If possible, the simplest solution is to create the nested maps manually before passing them to SnakeYaml. For instance, you can structure your input as follows:

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This approach directly builds the desired nested structure.

Option 2: Preprocessing Input for Nested Maps

If you're dealing with an existing HashMap where you can't change how the input map is structured, you’ll need to perform some preprocessing. This method involves writing a function to parse the keys and create the required nested structure. Below is a comprehensive breakdown of the steps needed:

Step 1: Create a Helper Method

You need to create a method, prepareInput, to transform your input map by processing the keys.

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Step 2: Split Keys and Merge Values

You also need to implement methods to split the keys and merge the values into the appropriate structure.

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Full Implementation

Here is the entire implementation of the conversion to nested YAML keys:

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Unit Testing the Solution

To validate that this works as expected, write unit tests to compare the output of your method against the expected nested structure.

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Conclusion

By following this guide, you can successfully transform dot separated keys in a HashMap into well-formed nested YAML objects using SnakeYaml. Whether you choose to build your nested maps directly or preprocess your input, you'll end up with a structured format that's easier to read and maintain. With these techniques, you'll enhance the usability of your YAML data structures in your Java applications.

Happy coding!