@PathVariable for URL parameters in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Spring Boot controller method?

Consider this Spring Boot controller method:

@GetMapping("/users/{id}")
public String getUser(@PathVariable String id) {
    return "User ID: " + id;
}

What will be the response body when a client requests /users/42?

Spring Boot

@GetMapping("/users/{id}")
public String getUser(@PathVariable String id) {
    return "User ID: " + id;
}

A User ID: 42

B User ID: {id}

C User ID: null

D 404 Not Found error

💡 Hint

The @PathVariable annotation binds the URL part to the method parameter.

The {id} in the URL path is captured and passed as the method parameter 'id'. So when the URL is /users/42, the method receives '42' as the id and returns 'User ID: 42'.

📝 Syntax

intermediate

Which option correctly uses @PathVariable with a different parameter name?

Given the URL pattern /items/{itemId}, which method signature correctly binds the path variable to a method parameter named id?

A

@GetMapping("/items/{itemId}")
public String getItem(@PathVariable("id") String id) { return id; }

B

@GetMapping("/items/{itemId}")
public String getItem(@PathVariable String itemId) { return id; }

C

@GetMapping("/items/{id}")
public String getItem(@PathVariable("itemId") String id) { return id; }

D

@GetMapping("/items/{itemId}")
public String getItem(@PathVariable("itemId") String id) { return id; }

💡 Hint

Use @PathVariable with the exact name of the path segment if the parameter name differs.

When the method parameter name differs from the path variable name, you must specify the path variable name inside @PathVariable("itemId"). Option D does this correctly.

🔧 Debug

advanced

What error occurs with this controller method?

Examine this Spring Boot controller method:

@GetMapping("/orders/{orderId}")
public String getOrder(@PathVariable int id) {
    return "Order: " + id;
}

What happens when a client requests /orders/123?

Spring Boot

@GetMapping("/orders/{orderId}")
public String getOrder(@PathVariable int id) {
    return "Order: " + id;
}

A HTTP 400 Bad Request due to type mismatch

B HTTP 400 Bad Request due to missing path variable binding

C HTTP 404 Not Found error

D Returns 'Order: 123' successfully

💡 Hint

Check if the method parameter name matches the path variable name or if @PathVariable specifies the name.

The path variable is named 'orderId' but the method parameter is 'id' without specifying @PathVariable("orderId"). Spring cannot bind the path variable to the parameter, causing a 400 Bad Request error.

❓ state_output

advanced

What is the output of this controller with multiple @PathVariable parameters?

Given this controller method:

@GetMapping("/books/{genre}/{id}")
public String getBook(@PathVariable String genre, @PathVariable int id) {
    return genre + "-" + id;
}

What is the response when the URL /books/scifi/7 is requested?

Spring Boot

@GetMapping("/books/{genre}/{id}")
public String getBook(@PathVariable String genre, @PathVariable int id) {
    return genre + "-" + id;
}

A books-scifi-7

B scifi-null

C scifi-7

D 7-scifi

💡 Hint

Each @PathVariable binds to the matching segment in the URL path.

The first path variable 'genre' gets 'scifi', and the second 'id' gets 7. The method returns 'scifi-7'.

🧠 Conceptual

expert

Which statement about @PathVariable is true?

Choose the correct statement about the use of @PathVariable in Spring Boot controllers.

A @PathVariable can bind multiple path segments separated by slashes into a single parameter using regex.

B @PathVariable requires the method parameter name to always match the path variable name in the URL.

C @PathVariable cannot be used with optional URL parameters.

D @PathVariable automatically converts path variables to any Java type without errors.

💡 Hint

Think about advanced usage of @PathVariable with patterns.

You can use regex in the path variable to capture multiple segments, e.g., @GetMapping("/files/{path:.+}") binds multiple path segments to 'path'.

Practice

1. What is the main purpose of the @PathVariable annotation in Spring Boot?

easy

A. To bind form data to a Java object

B. To handle exceptions in controller methods

C. To define a fixed URL mapping for a controller method

D. To extract values from the URL path and pass them as method parameters

Solution

1. Step 1: Understand the role of @PathVariable

   @PathVariable is used to get dynamic parts of the URL and pass them to method parameters.

2. Step 2: Compare with other annotations

   Other options like binding form data or exception handling are done by different annotations, not @PathVariable.

3. Final Answer:

   To extract values from the URL path and pass them as method parameters -> Option D

4. Quick Check:

   @PathVariable = extract URL values [OK]

Hint: Remember: @PathVariable grabs values directly from URL path [OK]

Common Mistakes:

• Confusing @PathVariable with @RequestParam
• Thinking it binds form data
• Assuming it handles exceptions

2. Which of the following is the correct syntax to use @PathVariable in a Spring Boot controller method to get an id from the URL /user/{id}?

easy

A. @GetMapping("/user/{id}") public String getUser(@PathVariable int id) { ... }

B. @GetMapping("/user") public String getUser(@PathVariable int id) { ... }

C. @GetMapping("/user/{id}") public String getUser(@RequestParam int id) { ... }

D. @GetMapping("/user/{id}") public String getUser(@PathVariable String name) { ... }

Solution

1. Step 1: Match URL pattern with method parameter

   The URL has {id}, so the method must have @PathVariable int id to match the placeholder.

2. Step 2: Check annotation and parameter type

   @GetMapping("/user/{id}") public String getUser(@PathVariable int id) { ... } correctly uses @PathVariable with int id and matches the URL pattern.

3. Final Answer:

   @GetMapping("/user/{id}") public String getUser(@PathVariable int id) { ... } -> Option A

4. Quick Check:

   URL {id} matches @PathVariable int id [OK]

Hint: URL placeholder and @PathVariable name must match [OK]

Common Mistakes:

• Missing {id} in URL path
• Using @RequestParam instead of @PathVariable
• Mismatching parameter name and URL placeholder

3. Given the following Spring Boot controller method:

@GetMapping("/product/{category}/{id}")
public String getProduct(@PathVariable String category, @PathVariable int id) {
    return category + "-" + id;
}

What will be the output when a client requests /product/electronics/42?

medium

A. electronics-42

B. 42-electronics

C. category-id

D. electronics42

Solution

1. Step 1: Identify parameter values from URL

   URL /product/electronics/42 means category = "electronics", id = 42.

2. Step 2: Understand return statement

   The method returns category + "-" + id, so it returns "electronics-42".

3. Final Answer:

   electronics-42 -> Option A

4. Quick Check:

   Return = category + "-" + id = electronics-42 [OK]

Hint: Match URL parts to parameters in order [OK]

Common Mistakes:

• Swapping parameter order
• Ignoring the dash '-' in return
• Confusing @PathVariable with @RequestParam

4. Consider this Spring Boot controller method:

@GetMapping("/order/{orderId}")
public String getOrder(@PathVariable int id) {
    return "Order: " + id;
}

What will happen when a client requests /order/100?

medium

A. Returns "Order: 0"

B. Returns "Order: 100"

C. Throws an error because parameter name does not match path variable

D. Returns null

Solution

1. Step 1: Check URL placeholder and method parameter names

   URL has {orderId}, but method parameter is named id without specifying name in @PathVariable.

2. Step 2: Understand default matching behavior

   Without specifying the name in @PathVariable, Spring tries to match parameter name to path variable name. They differ, causing an error.

3. Final Answer:

   Throws an error because parameter name does not match path variable -> Option C

4. Quick Check:

   Parameter name must match path variable or specify name [OK]

Hint: Parameter name must match path variable or use @PathVariable("name") [OK]

Common Mistakes:

• Assuming names can differ without annotation
• Ignoring the need to specify variable name in @PathVariable
• Expecting default value assignment

5. You want to create a Spring Boot controller method that handles URLs like /blog/{year}/{month}/{slug} where year and month are integers and slug is a string. Which of the following method signatures correctly uses @PathVariable to extract these values?

hard

A. @GetMapping("/blog/{year}/{month}/{slug}")
public String getPost(@PathVariable int yr, @PathVariable int mo, @PathVariable String sl) { ... }

B. @GetMapping("/blog/{year}/{month}/{slug}")
public String getPost(@PathVariable("year") int y, @PathVariable("month") int m, @PathVariable("slug") String s) { ... }

C. @GetMapping("/blog/{year}/{month}/{slug}")
public String getPost(@PathVariable String year, @PathVariable String month, @PathVariable String slug) { ... }

D. @GetMapping("/blog/{year}/{month}/{slug}")
public String getPost(@PathVariable int y, @PathVariable int m, @PathVariable String s) { ... }

Solution

1. Step 1: Match URL placeholders with method parameters

   The URL has {year}, {month}, {slug}. Method parameters must match these names or specify them explicitly.

2. Step 2: Check parameter names and @PathVariable usage

   @GetMapping("/blog/{year}/{month}/{slug}") public String getPost(@PathVariable("year") int y, @PathVariable("month") int m, @PathVariable("slug") String s) { ... } uses different parameter names (y, m, s) but explicitly maps them to URL placeholders using @PathVariable("name"), which is correct.

3. Final Answer:

   @GetMapping("/blog/{year}/{month}/{slug}") public String getPost(@PathVariable("year") int y, @PathVariable("month") int m, @PathVariable("slug") String s) { ... } -> Option B

4. Quick Check:

   Explicit name mapping allows different parameter names [OK]

Hint: Use @PathVariable("name") if parameter name differs from URL placeholder [OK]

Common Mistakes:

• Using mismatched parameter names without specifying name
• Using wrong data types for year/month
• Assuming parameter names must always match URL placeholders