How Do You Read Query Parameters in Spring Boot?

Introduction ## Core Concepts ## What Are Query Parameters? ## How Spring Boot Reads Query Parameters ## Why Use Query Parameters? ## Code Examples (End-to-End) ## ✅ Example 1: Reading Simple Query Parameters with @RequestParam ## Use Case ## Step 1: REST Controller ## 🔍 How It Works ## ✅ Example 2: Optional Query Parameters, Defaults & Pagination ## Use Case ## Step 2: REST Controller with Optional Params ## 🔍 Behavior Explained ## 🧠 Bonus: Multiple Query Parameters as a Map ## Best Practices ## Conclusion ## Call to Action ## 🔗 Helpful Resources Learn how to read query parameters in Spring Boot using @RequestParam with clear, beginner-friendly explanations and Java 21 end-to-end examples. Imagine you’re shopping online and you click a link like this: Behind the scenes, the server reads those query parameters (category, sort, page) to decide what data to return and how to return it. In Spring Boot, reading query parameters is one of the most common tasks when building REST APIs. Whether you’re filtering products, paginating results, or toggling features, query parameters are your go-to tool. In this blog, you’ll learn how to read query parameters in Spring Boot, using simple explanations, real-world analogies, and end-to-end Java 21 examples. Query parameters are key–value pairs appended to a URL after the ? symbol. 🧠 Think of query parameters as options on a remote control—same TV (endpoint), different behavior based on buttons pressed. Spring Boot provides the @RequestParam annotation to: ✅ Filtering data ✅ Sorting results ✅ Pagination ✅ Feature flags ✅ Optional inputs (without changing the endpoint) Fetch users filtered by role and active status. Search products with optional filters and pagination. Spring Boot automatically: ✔ Useful for dynamic filtering ✔ Common in search APIs Always use default values for pagination Avoid unexpected 400 errors. Prefer query params for optional data Path variables should represent mandatory identifiers. Validate query parameters Combine @Validated with constraints like @Min. Use meaningful parameter names page is better than p. Avoid too many query parameters Complex filters may need a request body. Reading query parameters is a fundamental skill for building REST APIs with Spring Boot. you can build flexible, user-friendly APIs that adapt to different client needs. Mastering reading query parameters in Spring Boot will significantly improve your confidence in Java programming and help you learn Java with real-world practices. 💬 Have questions about query parameters or REST API design? 👇 Drop them in the comments! Want advanced topics next? Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse CODE_BLOCK: /products?category=mobile&sort=price&page=1 Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: /products?category=mobile&sort=price&page=1 CODE_BLOCK: /products?category=mobile&sort=price&page=1 CODE_BLOCK: /users?role=admin&active=true Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: /users?role=admin&active=true CODE_BLOCK: /users?role=admin&active=true CODE_BLOCK: package com.example.demo.controller; import org.springframework.web.bind.annotation.*; @RestController @RequestMapping("/users") public class UserController { /** * Example URL: * /users?role=admin&active=true */ @GetMapping public String getUsers( @RequestParam String role, @RequestParam boolean active) { return "Fetching users with role=" + role + ", active=" + active; } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: package com.example.demo.controller; import org.springframework.web.bind.annotation.*; @RestController @RequestMapping("/users") public class UserController { /** * Example URL: * /users?role=admin&active=true */ @GetMapping public String getUsers( @RequestParam String role, @RequestParam boolean active) { return "Fetching users with role=" + role + ", active=" + active; } } CODE_BLOCK: package com.example.demo.controller; import org.springframework.web.bind.annotation.*; @RestController @RequestMapping("/users") public class UserController { /** * Example URL: * /users?role=admin&active=true */ @GetMapping public String getUsers( @RequestParam String role, @RequestParam boolean active) { return "Fetching users with role=" + role + ", active=" + active; } } CODE_BLOCK: package com.example.demo.controller; import org.springframework.web.bind.annotation.*; @RestController @RequestMapping("/products") public class ProductController { /** * Example URL: * /products?category=laptop&page=1&size=10 */ @GetMapping public String searchProducts( @RequestParam(required = false) String category, @RequestParam(defaultValue = "0") int page, @RequestParam(defaultValue = "20") int size) { return String.format( "Searching products [category=%s, page=%d, size=%d]", category, page, size); } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: package com.example.demo.controller; import org.springframework.web.bind.annotation.*; @RestController @RequestMapping("/products") public class ProductController { /** * Example URL: * /products?category=laptop&page=1&size=10 */ @GetMapping public String searchProducts( @RequestParam(required = false) String category, @RequestParam(defaultValue = "0") int page, @RequestParam(defaultValue = "20") int size) { return String.format( "Searching products [category=%s, page=%d, size=%d]", category, page, size); } } CODE_BLOCK: package com.example.demo.controller; import org.springframework.web.bind.annotation.*; @RestController @RequestMapping("/products") public class ProductController { /** * Example URL: * /products?category=laptop&page=1&size=10 */ @GetMapping public String searchProducts( @RequestParam(required = false) String category, @RequestParam(defaultValue = "0") int page, @RequestParam(defaultValue = "20") int size) { return String.format( "Searching products [category=%s, page=%d, size=%d]", category, page, size); } } COMMAND_BLOCK: @GetMapping("/search") public String search(@RequestParam Map<String, String> params) { return "Query params received: " + params; } Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: @GetMapping("/search") public String search(@RequestParam Map<String, String> params) { return "Query params received: " + params; } COMMAND_BLOCK: @GetMapping("/search") public String search(@RequestParam Map<String, String> params) { return "Query params received: " + params; } CODE_BLOCK: Enter fullscreen mode Exit fullscreen mode - role → admin - active → true - Extract values from the URL - Automatically convert them to Java types - Handle optional and required parameters - @RequestParam is required - Missing values cause 400 BAD_REQUEST - Converts query params to Java types - Applies default values - Handles missing optional params safely - Always use default values for pagination Avoid unexpected 400 errors. - Prefer query params for optional data Path variables should represent mandatory identifiers. - Validate query parameters Combine @Validated with constraints like @Min. - Use meaningful parameter names page is better than p. - Avoid too many query parameters Complex filters may need a request body. - @RequestParam - Optional parameters - Default values - Validation for query params - Pagination with Pageable - API design best practices - Spring @RequestParam Documentation - Spring Boot REST API Guide - Oracle Java Documentation