Handling path variables and query params together in Spring Boot

Introduction

We use path variables and query parameters together to get specific and flexible information from a web request. Path variables identify a resource, and query parameters filter or add details.

When you want to get a user by ID and also filter their posts by date.

When you need to fetch a product by its category and sort the results by price.

When you want to access a blog post by its slug and specify the number of comments to show.

When you want to get details of an order by order number and include optional status filters.

Syntax

Spring Boot

@GetMapping("/resource/{id}")
public ResponseEntity<?> methodName(@PathVariable Type id, @RequestParam(required = false) Type param) {
    // method body
}

@PathVariable extracts values from the URL path.

@RequestParam extracts query parameters from the URL after the question mark.

Examples

This method gets a user ID from the path and an optional filter from the query string.

Spring Boot

@GetMapping("/users/{userId}")
public String getUser(@PathVariable String userId, @RequestParam(required = false) String filter) {
    return "User: " + userId + ", Filter: " + filter;
}

This method gets a product category from the path and a sort order from the query, defaulting to ascending.

Spring Boot

@GetMapping("/products/{category}")
public String getProducts(@PathVariable String category, @RequestParam(defaultValue = "asc") String sort) {
    return "Category: " + category + ", Sort: " + sort;
}

Sample Program

This Spring Boot controller has a method that takes an item ID from the URL path and an optional color from the query parameters. It returns a simple string showing both values.

Spring Boot

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ItemController {

    @GetMapping("/items/{itemId}")
    public String getItemDetails(@PathVariable String itemId, @RequestParam(required = false) String color) {
        if (color == null) {
            return "Item ID: " + itemId + ", Color: not specified";
        }
        return "Item ID: " + itemId + ", Color: " + color;
    }
}

Important Notes

If a query parameter is optional, set required = false to avoid errors when it's missing.

You can provide default values for query parameters using defaultValue in @RequestParam.

Path variables are part of the URL structure, while query parameters come after a question mark and can be many or none.

Summary

Use @PathVariable to get parts of the URL path.

Use @RequestParam to get query parameters after the URL path.

Combining both lets you build flexible and clear web endpoints.

Practice

1. In Spring Boot, which annotation is used to extract a value from the URL path segment in a controller method?

easy

A. @PathVariable

B. @RequestParam

C. @RequestBody

D. @RequestHeader

Solution

1. Step 1: Understand URL parts

   The URL path segment is the part of the URL that defines the resource location, like /users/{id}.

2. Step 2: Identify the correct annotation

   @PathVariable is used to bind a method parameter to a URI template variable in the path.

3. Final Answer:

   @PathVariable -> Option A

4. Quick Check:

   Path segment value = @PathVariable [OK]

Hint: Use @PathVariable for URL path parts, not query strings [OK]

Common Mistakes:

• Confusing @RequestParam with @PathVariable
• Using @RequestBody for path variables
• Trying to get path variables from headers

2. Which of the following method signatures correctly handles a path variable id and a query parameter sort in Spring Boot?

easy

A. public String getUser(@PathVariable String id, @RequestParam String sort)

B. public String getUser(@RequestParam String id, @PathVariable String sort)

C. public String getUser(@RequestParam String id, @RequestParam String sort)

D. public String getUser(@PathVariable String id, @PathVariable String sort)

Solution

1. Step 1: Match annotations to parameter types

   Path variables come from the URL path, so use @PathVariable for id. Query parameters come after ?, so use @RequestParam for sort.

2. Step 2: Check method signature correctness

   public String getUser(@PathVariable String id, @RequestParam String sort) correctly uses @PathVariable for id and @RequestParam for sort.

3. Final Answer:

   public String getUser(@PathVariable String id, @RequestParam String sort) -> Option A

4. Quick Check:

   Path variable = @PathVariable, Query param = @RequestParam [OK]

Hint: Path variables use @PathVariable, query params use @RequestParam [OK]

Common Mistakes:

• Swapping @PathVariable and @RequestParam
• Using @PathVariable for query parameters
• Missing one of the annotations

3. Given the controller method:

@GetMapping("/items/{itemId}")
public String getItem(@PathVariable String itemId, @RequestParam(defaultValue = "asc") String order) {
    return itemId + "-" + order;
}

What will be the output when a client requests /items/42?order=desc?

medium

A. "42-asc"

B. "42-desc"

C. "desc-42"

D. Runtime error due to missing parameter

Solution

1. Step 1: Identify values from URL

   Path variable itemId is "42" from /items/42. Query parameter order is "desc" from ?order=desc.

2. Step 2: Understand method return

   The method returns itemId + "-" + order, so "42-desc".

3. Final Answer:

   "42-desc" -> Option B

4. Quick Check:

   Path variable + query param = "42-desc" [OK]

Hint: Path variable fills {itemId}, query param fills order value [OK]

Common Mistakes:

• Ignoring query parameter and using default
• Mixing order of concatenation
• Expecting error when query param is present

4. Consider this controller method:

@GetMapping("/books/{bookId}")
public String getBook(@PathVariable int bookId, @RequestParam int page) {
    return "Book: " + bookId + ", Page: " + page;
}

What error will occur if a client calls /books/abc?page=2?

medium

A. 404 Not Found because path variable missing

B. 500 Internal Server Error due to null page

C. 400 Bad Request due to type mismatch

D. No error, returns "Book: abc, Page: 2"

Solution

1. Step 1: Check path variable type

   The method expects bookId as int, but URL provides "abc" which is not a number.

2. Step 2: Understand Spring Boot behavior on type mismatch

   Spring Boot returns 400 Bad Request when it cannot convert path variable to required type.

3. Final Answer:

   400 Bad Request due to type mismatch -> Option C

4. Quick Check:

   Type mismatch in @PathVariable causes 400 error [OK]

Hint: Non-numeric path variable for int causes 400 error [OK]

Common Mistakes:

• Expecting 404 Not Found instead of 400
• Assuming null page causes error
• Thinking method returns string with invalid input

5. You want to create a Spring Boot endpoint that handles a user ID as a path variable and optionally accepts a query parameter filter. If filter is missing, it should default to "all". Which method signature correctly implements this behavior?

hard

A. public String getUser(@PathVariable String userId, @RequestParam Optional<String> filter)

B. public String getUser(@RequestParam String userId, @RequestParam String filter)

C. public String getUser(@PathVariable String userId, @RequestParam(required = true) String filter)

D. public String getUser(@PathVariable String userId, @RequestParam(defaultValue = "all") String filter)

Solution

1. Step 1: Identify path variable usage

   User ID is part of the URL path, so use @PathVariable for userId.

2. Step 2: Handle optional query parameter with default

   Use @RequestParam with defaultValue = "all" to provide a default when filter is missing.

3. Final Answer:

   public String getUser(@PathVariable String userId, @RequestParam(defaultValue = "all") String filter) -> Option D

4. Quick Check:

   Default query param value = @RequestParam(defaultValue) [OK]

Hint: Use @RequestParam(defaultValue) for optional query params [OK]

Common Mistakes:

• Using @RequestParam(required = true) for optional params
• Using @RequestParam without defaultValue causing errors
• Confusing @RequestParam and @PathVariable roles