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Learn how to effectively `pass multiple values` in RequestParam in Spring Boot and retrieve them as a list. A simple guide to ensure proper handling of optional query parameters.
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How to Pass Multiple Values in RequestParam in Spring Boot

In web applications, it's common to send multiple values through query parameters. However, when using Spring Boot, developers often encounter challenges—particularly when those parameters are optional or when they contain specific formatting. In this post, we will address how to pass multiple values in a RequestParam effectively and retrieve them correctly.

Understanding the Problem

Imagine a scenario where you need to query several values, such as filters or options, and want to retrieve them in a list format. For instance, you might want to send a query that includes variables like a, b, and c, but you often find that even if you only send b, the results may include unwanted empty strings or formatting issues, such as:

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When you call it with optional values, like ",b,", you might end up retrieving an array that looks like this:

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This is not ideal. The aim is to ensure that you retrieve exactly the values you passed, without any empty entries. Let's delve into the solution for this issue.

Solution: Distinct List Params

To effectively handle multiple values through a RequestParam in Spring Boot, it’s crucial to declare them correctly in your controller method. Instead of attempting to manage a single parameter, it's preferable to define distinct parameters for each query value. This way, you can gather multiple pieces of data efficiently. Here’s how to do it:

Example Implementation

In your Spring Boot application, you could define a method in your controller that looks like this:

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How It Works

Define Distinct Parameters: The method foo uses the @ RequestParam annotation for param1, param2, and param3, each of which can accept multiple values.

Sending the Request: You can send a request like /your-resource?param1=1,2,3&param2=4,5&param3=10.

Automatic Handling: Spring Boot automatically converts the comma-separated values into a List of Strings. For example:

param1 will contain [1, 2, 3]

param2 will contain [4, 5]

param3 will contain [10]

Benefits of This Approach

Clarity: Each parameter is clearly defined, making it easy for anyone reviewing the code to understand what values are expected.

Error Reduction: By having distinct parameters, you reduce the risk of dealing with unwanted empty strings or malformed data.

Flexibility: You can easily modify the parameters or add new ones without affecting the existing structure of your query.

Conclusion

By using distinct List parameters in your Spring Boot controllers, you can efficiently handle multiple values passed through RequestParams. This not only improves the clarity of your code but also minimizes errors and ensures that you receive the exact values you intend to work with. If you're developing web applications that rely on query parameters, implementing this strategy will save you time and frustration in the long run.

Feel free to reach out with any questions or additional scenarios you’d like to explore regarding RequestParams in Spring Boot. Happy coding!