@RequestParam for query strings in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing the endpoint with query ?name=John

Consider this Spring Boot controller method:

@GetMapping("/greet")
public String greet(@RequestParam String name) {
    return "Hello, " + name + "!";
}

What will be the response body when you visit /greet?name=John?

Spring Boot

@GetMapping("/greet")
public String greet(@RequestParam String name) {
    return "Hello, " + name + "!";
}

A "Hello, John!"

B "Hello, null!"

C HTTP 400 Bad Request error

D "Hello, !"

💡 Hint

The @RequestParam annotation binds the query string parameter to the method argument.

The query string parameter 'name' is passed as 'John', so the method returns 'Hello, John!'.

❓ state_output

intermediate

What happens if the query parameter is missing?

Given this method:

@GetMapping("/welcome")
public String welcome(@RequestParam String user) {
    return "Welcome, " + user;
}

What happens when you call /welcome without any query parameters?

Spring Boot

@GetMapping("/welcome")
public String welcome(@RequestParam String user) {
    return "Welcome, " + user;
}

A HTTP 500 Internal Server Error

B "Welcome, null"

C HTTP 400 Bad Request error

D "Welcome, "

💡 Hint

By default, @RequestParam is required unless specified otherwise.

Since 'user' parameter is required by default and missing, Spring returns 400 Bad Request.

📝 Syntax

advanced

Which option correctly sets a default value for a missing query parameter?

You want to make the query parameter optional and provide a default value "Guest" if missing. Which method signature is correct?

A

@GetMapping("/hello")
public String hello(@RequestParam(required = false, default = "Guest") String name) {
    return "Hi, " + name;
}

B

@GetMapping("/hello")
public String hello(@RequestParam(defaultValue = "Guest") String name) {
    return "Hi, " + name;
}

C

@GetMapping("/hello")
public String hello(@RequestParam(required = true, defaultValue = "Guest") String name) {
    return "Hi, " + name;
}

D

@GetMapping("/hello")
public String hello(@RequestParam(optional = true, defaultValue = "Guest") String name) {
    return "Hi, " + name;
}

💡 Hint

The correct attribute name for default value is 'defaultValue'.

Option B uses the correct attribute 'defaultValue' and does not set 'required' which defaults to true but is overridden by defaultValue.

🔧 Debug

advanced

Why does this code cause a 400 error when calling /search without parameters?

Look at this method:

@GetMapping("/search")
public String search(@RequestParam String query, @RequestParam(required = false) Integer page) {
    return "Searching for " + query + " on page " + (page == null ? 1 : page);
}

Why does calling /search without query parameters cause a 400 error?

Spring Boot

@GetMapping("/search")
public String search(@RequestParam String query, @RequestParam(required = false) Integer page) {
    return "Searching for " + query + " on page " + (page == null ? 1 : page);
}

A Because 'query' is required and missing in the request

B Because the method returns a String instead of ResponseEntity

C Because both parameters are required by default

D Because 'page' is an Integer and cannot be null

💡 Hint

Check which parameters are required by default.

'query' is required by default and missing causes 400 Bad Request. 'page' is optional.

🧠 Conceptual

expert

How does Spring handle multiple values for the same query parameter?

Given this method:

@GetMapping("/filter")
public String filter(@RequestParam List tags) {
    return "Tags: " + String.join(",", tags);
}

What is the output when calling /filter?tags=java&tags=spring&tags=boot?

Spring Boot

@GetMapping("/filter")
public String filter(@RequestParam List<String> tags) {
    return "Tags: " + String.join(",", tags);
}

A "Tags: java"

B "Tags: [java, spring, boot]"

C HTTP 400 Bad Request error

D "Tags: java,spring,boot"

💡 Hint

Spring can bind multiple query parameters with the same name into a List.

Spring collects all 'tags' parameters into the List and joins them with commas.