How to Use Spring Boot SpEL to Concatenate Variables and Convert to Lowercase

Discover how to leverage `Spring Expression Language (SpEL)` in Spring Boot to concatenate variables and convert the entire expression into lowercase for optimized key management.
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Leveraging Spring Boot SpEL for Concatenation and Lowercase Conversion

In Spring Boot development, you may often find yourself needing to create a unique key for caching purposes. This task can become slightly more complex when additional formatting, such as converting to lowercase, is required. In this guide, we will explore a common situation where we want to concatenate multiple variables and convert the resulting string into lowercase using Spring Expression Language (SpEL).

The Problem

Consider the following method signature, where we define a caching mechanism:

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In this validate method, we're using SpEL to create a key for caching. The key combines three variables: name, age, and country. However, we have an additional requirement: we need to ensure that the entire concatenated string is converted to lowercase.

For instance, if someone invokes this method as follows:

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We want the resulting key to be:

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The Solution

To achieve this, we can modify our SpEL expression to include a method that converts the entire concatenated result to lowercase. Here’s how you can do this effectively:

Step-by-Step Breakdown

Create a SpEL Expression
We will use the SpelExpressionParser to create our SpEL expression that concatenates the input variables and converts the result to lowercase.

Set Context Variables
We need to set our context variables which will hold the values we want to concatenate.

Execute and Fetch the Value
Finally, we will execute the expression and print the result to verify that it produces the desired output.

Sample Code

Here’s how you can implement this solution in your Spring Boot application:

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Explanation of the Code

SpelExpressionParser: This class parses the string expression.

parseExpression Method: Here we define our operation which consists of concatenating foo and bar with :: and then converting the result to lowercase using the .toLowerCase() method.

StandardEvaluationContext: This is the execution context where we set our variables (foo and bar).

Conclusion

By following the steps outlined above, you can successfully concatenate multiple variables within a SpEL expression and convert the entire result to lowercase. This approach gives you more control over how your keys are formed, ensuring they are consistent and formatted as intended.

Feel free to implement this in your own Spring Boot application, and you can enjoy the benefits of a cleaner and more systematic approach to key management in your caching strategy!