How to Convert ConcurrentHashMap into Guava Cache Key, Pair

Описание: Discover how to effectively convert a `ConcurrentHashMap` with pairs into a `Guava Cache Key, Pair ` using clear and simple implementation steps.
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This video is based on the question https://stackoverflow.com/q/63265508/ asked by the user 'Martin' ( https://stackoverflow.com/u/10596295/ ) and on the answer https://stackoverflow.com/a/63266441/ provided by the user 'Rishabh Sharma' ( https://stackoverflow.com/u/13958041/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Convert ConcurrentHashMap into Guava Cache<Key, Pair>

When working with Java, you may occasionally encounter the need to transition between different data structures. A common scenario is converting a ConcurrentHashMap containing key-value pairs into a Guava Cache. This guide will guide you through the process, specifically focusing on how to transform data returned by the getAllOldAndNewPairs() method into a Guava Cache<Key, Pair>.

Problem Statement

You have the following method that returns a ConcurrentMap<String, String> representing old and new number pairs:

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You want to fill a Guava cache with these pairs, but you are facing type mismatch errors due to your current approach.

Solution Overview

To effectively fill a Guava Cache with the contents of a ConcurrentHashMap, you need to leverage the putAll method from the Guava Cache interface. Below, I will provide step-by-step guidance to help you achieve this.

Understanding the CacheLoader

The LoadingCache in Guava is designed for situations where you want the cache to automatically load values if they are not present. However, the method you have used incorrectly suggests returning a ConcurrentMap, which leads to the type mismatch. Let’s clarify how to use a CacheLoader properly.

Step-by-Step Solution

Define the Cache Structure: The cache key will be a String, while the value will be a String that represents the new number.

Create a Proper LoadingCache: Instead of trying to return the entire map, you need to configure the cache loading logic correctly:

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Populate the Cache: After defining the cache, you can load it with pairs using putAll. Here’s how:

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Complete Implementation

Putting it all together, your complete implementation could look like this:

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Conclusion

By following these steps, you can successfully convert a ConcurrentHashMap into a Guava Cache<Key, Pair>. Utilizing the putAll method and a properly defined CacheLoader allows you to efficiently manage the pairing of old and new numbers while leveraging the benefits of caching.

Experiment with these changes, and soon you'll have a sleek and efficient caching mechanism within your Java applications. Happy coding!