How do you handle query parameters in Spring MVC?

Table of Contents

Introduction

In Spring MVC, query parameters are a common way for clients to send additional information in the URL. For example, a query parameter can be used to filter results, specify search criteria, or control pagination. Spring MVC makes it easy to access these parameters through the @RequestParam annotation, which allows you to capture parameters from the URL and bind them to method parameters in your controller.

In this guide, we will walk you through how to handle query parameters in Spring MVC, explaining how to retrieve, validate, and use query parameters effectively in your web applications.

1. Basic Query Parameter Handling with **@RequestParam**

The most common way to access query parameters in Spring MVC is by using the @RequestParam annotation. This annotation binds the value of the query parameter in the request URL to a method parameter in your controller.

Example: Basic Query Parameter Handling

Consider the following example where a controller accepts a search query as a query parameter.

URL Example:

  • http://localhost:8080/search?query=laptop

Explanation:

  • **@RequestParam**: Binds the query parameter from the URL to the method parameter query.
  • When a client requests /search?query=laptop, the response will be "Searching for: laptop".

2. Handling Optional Query Parameters

Sometimes, query parameters are optional, meaning they may or may not be included in the request. In such cases, Spring provides an option to make the parameter optional by specifying a default value or using Optional<T> from Java 8.

Example: Optional Query Parameters

URL Examples:

  • http://localhost:8080/search?query=laptop → "Searching for: laptop"
  • http://localhost:8080/search → "Searching for: all"

Explanation:

  • **required = false**: Makes the query parameter optional.
  • **defaultValue = "all"**: Specifies the default value to be used when the query parameter is not provided in the request.

Alternatively, you can use Optional<T> for more flexibility:

URL Examples:

  • http://localhost:8080/search?query=laptop → "Searching for: laptop"
  • http://localhost:8080/search → "Searching for: all"

3. Multiple Query Parameters

You can also handle multiple query parameters in a single method by specifying multiple @RequestParam annotations for each parameter.

Example: Multiple Query Parameters

URL Example:

  • http://localhost:8080/products?category=electronics&limit=5&sort=price

Explanation:

  • The method takes three parameters: category, limit, and sort.
  • **category** is required.
  • **limit** is optional with a default value of 10.
  • **sort** is optional and can be null if not provided.

4. Binding Multiple Values to a Single Parameter

Spring MVC allows you to bind multiple values of a query parameter to a collection type, such as a List or Set. This is useful when you expect a parameter to have multiple values in the query string.

Example: Handling Multiple Values for a Query Parameter

URL Example:

  • http://localhost:8080/categories?categories=electronics&categories=clothing&categories=home

Explanation:

  • **List<String> categories**: Spring binds the multiple values of the categories query parameter to a List of strings.
  • The response will be "Categories: electronics, clothing, home".

5. Customizing the Parameter Binding

Spring provides various ways to customize how query parameters are bound to method parameters, including conversion and validation.

Example: Custom Type Conversion

URL Example:

  • http://localhost:8080/products?minPrice=100&maxPrice=500

Explanation:

  • Spring automatically converts the query parameters minPrice and maxPrice from string to Double before passing them to the method.

Example: Custom Validator for Query Parameters

You can use Spring’s built-in validation annotations to validate query parameters.

URL Example:

  • http://localhost:8080/products?page=1

Explanation:

  • **@Min(1)**: Ensures that the page parameter is at least 1. If not, Spring will throw a ConstraintViolationException.

6. Handling Complex Query Parameters with a Custom Object

Sometimes, it makes sense to encapsulate multiple query parameters into a custom object. You can use @ModelAttribute to bind multiple query parameters to a single Java object.

Example: Binding Multiple Parameters to a Custom Object

URL Example:

  • http://localhost:8080/products?category=electronics&brand=Samsung&minPrice=100

Explanation:

  • **@ModelAttribute**: Binds query parameters to the fields of the ProductSearchCriteria object.
  • Spring automatically maps the query parameters (category, brand, minPrice) to the fields of the object.

7. Conclusion

Handling query parameters in Spring MVC is straightforward and flexible. The @RequestParam annotation provides an easy way to access and bind query parameters to controller method parameters. You can handle optional parameters, validate them, bind multiple values to collections, and even use custom objects to encapsulate complex query data. With Spring’s powerful parameter binding features, you can efficiently manage query parameters and ensure that your application handles client requests in a clean and scalable manner.

Key points to remember:

  • Use @RequestParam to bind query parameters to method parameters.
  • Make query parameters optional with required=false or Optional<T>.
  • Handle multiple values for a parameter with List or Set.
  • Use custom objects and @ModelAttribute for complex query parameter mappings.
  • Validate query parameters using Spring’s built-in annotations.
Share
Similar Questions