@PostMapping for POST requests in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @PostMapping annotation in Spring Boot?

@PostMapping is used to map HTTP POST requests to specific handler methods in a Spring Boot controller. It tells the app to run that method when a POST request is received at the specified URL.

beginner

How do you specify the URL path for a POST request handler using @PostMapping?

You add the path as a parameter inside @PostMapping, like @PostMapping("/submit"). This means the method handles POST requests sent to /submit.

intermediate

Can @PostMapping handle form data and JSON data? How?

Yes. For form data, you can use @RequestParam or @ModelAttribute. For JSON, use @RequestBody to automatically convert JSON into a Java object.

beginner

What HTTP method does @PostMapping specifically handle?

@PostMapping handles only HTTP POST requests, which are typically used to send data to the server to create or update resources.

intermediate

How is @PostMapping different from @RequestMapping?

@PostMapping is a shortcut for @RequestMapping(method = RequestMethod.POST). It is simpler and clearer when you only want to handle POST requests.

Which HTTP method does @PostMapping handle?

A POST

B GET

C PUT

D DELETE

@PostMapping is designed to handle POST requests only.

How do you specify the URL path for a POST request handler?

A Inside <code>@PathVariable</code>

B Inside <code>@PostMapping("/path")</code>

C Inside <code>@RequestParam</code>

D Inside <code>@GetMapping("/path")</code>

The URL path is given as a parameter to @PostMapping.

Which annotation is used to convert JSON request body into a Java object in a POST handler?

A @RequestBody

B @RequestParam

C @PathVariable

D @ModelAttribute

@RequestBody tells Spring to convert JSON data into a Java object.

What is the main difference between @PostMapping and @RequestMapping?

A <code>@RequestMapping</code> only handles POST

B <code>@PostMapping</code> handles all HTTP methods

C <code>@PostMapping</code> is a shortcut for POST requests only

D They are exactly the same

@PostMapping is a simpler way to handle POST requests specifically.

Which annotation would you use to get form data parameters in a POST request?

A @RequestBody

B @PathVariable

C @PostMapping

D @RequestParam

@RequestParam extracts form data parameters from the request.

Explain how @PostMapping works in a Spring Boot controller and how you handle JSON data in the POST request.

Think about how the server knows which method to run for a POST request and how it reads JSON data.

Describe the difference between @PostMapping and @RequestMapping when handling POST requests.

Focus on the HTTP methods each annotation supports and code clarity.

Practice

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

easy

A. To map HTTP PUT requests to a specific method

B. To map HTTP POST requests to a specific method

C. To map HTTP DELETE requests to a specific method

D. To map HTTP GET requests to a specific method

Solution

1. Step 1: Understand HTTP methods

   HTTP POST is used to send data to the server, so a method handling POST requests must be mapped accordingly.

2. Step 2: Role of @PostMapping

   @PostMapping specifically maps HTTP POST requests to a method in a Spring Boot controller.

3. Final Answer:

   To map HTTP POST requests to a specific method -> Option B

4. Quick Check:

   @PostMapping = POST request handler [OK]

Hint: POST requests use @PostMapping to connect URL and method [OK]

Common Mistakes:

• Confusing @PostMapping with @GetMapping
• Using @PostMapping for GET requests
• Not understanding HTTP method differences

2. Which of the following is the correct syntax to create a POST endpoint in Spring Boot that accepts JSON data?

easy

A. @PostMapping("/submit")
public String submitData(String data) { return "Received"; }

B. @GetMapping("/submit")
public String submitData(@RequestBody String data) { return "Received"; }

C. @PostMapping("/submit")
public String submitData(@RequestBody String data) { return "Received"; }

D. @PostMapping("/submit")
public String submitData(@RequestParam String data) { return "Received"; }

Solution

1. Step 1: Identify correct annotation and parameter

   The method must use @PostMapping to handle POST requests and @RequestBody to receive JSON data from the request body.

2. Step 2: Check each option

   @PostMapping("/submit") public String submitData(@RequestBody String data) { return "Received"; } uses @PostMapping and @RequestBody correctly. @GetMapping("/submit") public String submitData(@RequestBody String data) { return "Received"; } uses @GetMapping which is wrong. @PostMapping("/submit") public String submitData(String data) { return "Received"; } misses @RequestBody, so data won't be parsed from JSON. @PostMapping("/submit") public String submitData(@RequestParam String data) { return "Received"; } uses @RequestParam which reads query parameters, not JSON body.

3. Final Answer:

   @PostMapping("/submit") public String submitData(@RequestBody String data) { return "Received"; } -> Option C

4. Quick Check:

   @PostMapping + @RequestBody = correct syntax [OK]

Hint: Use @RequestBody to get JSON data in POST method [OK]

Common Mistakes:

• Using @GetMapping instead of @PostMapping
• Forgetting @RequestBody for JSON input
• Using @RequestParam for JSON body data

3. Given the following Spring Boot controller method, what will be the output when a POST request with body "Hello" is sent to /greet? @PostMapping("/greet") public String greet(@RequestBody String name) { return "Hi, " + name + "!"; }

medium

A. "Hi, Hello!"

B. "Hello"

C. "Hi, name!"

D. HTTP 404 Not Found

Solution

1. Step 1: Understand method behavior

   The method takes the request body as a String parameter named 'name' and returns "Hi, " plus that name plus "!".

2. Step 2: Apply input to output

   Input body is "Hello", so the output will be "Hi, Hello!".

3. Final Answer:

   "Hi, Hello!" -> Option A

4. Quick Check:

   Input "Hello" returns "Hi, Hello!" [OK]

Hint: Return greeting by concatenating input string [OK]

Common Mistakes:

• Ignoring @RequestBody and expecting query param
• Confusing output with input
• Assuming endpoint is missing (404)

4. Identify the error in this Spring Boot POST method: @PostMapping("/addUser") public String addUser(String user) { return "User " + user + " added"; }

medium

A. Method return type should be void

B. Incorrect HTTP method annotation, should be @GetMapping

C. Missing @PathVariable annotation

D. Missing @RequestBody annotation for 'user' parameter

Solution

1. Step 1: Check parameter binding

   The method expects to receive data in the POST request body, so the parameter must be annotated with @RequestBody to bind JSON or raw data.

2. Step 2: Verify annotations

   Without @RequestBody, Spring won't map the request body to the 'user' parameter, causing it to be null or empty.

3. Final Answer:

   Missing @RequestBody annotation for 'user' parameter -> Option D

4. Quick Check:

   POST body needs @RequestBody on parameter [OK]

Hint: Add @RequestBody to method parameter for POST data [OK]

Common Mistakes:

• Forgetting @RequestBody on POST method parameters
• Using @GetMapping for POST endpoints
• Confusing @PathVariable with request body

5. You want to create a Spring Boot POST endpoint /register that accepts a JSON object with fields username and email, maps it to a Java record UserData(String username, String email), and returns a confirmation message. Which method signature correctly implements this?

hard

A. @PostMapping("/register")
public String registerUser(@RequestBody UserData user) {
return "User " + user.username() + " registered with email " + user.email();
}

B. @PostMapping("/register")
public String registerUser(UserData user) {
return "User " + user.username() + " registered";
}

C. @PostMapping("/register")
public String registerUser(@RequestParam UserData user) {
return "User " + user.username() + " registered";
}

D. @PostMapping("/register")
public String registerUser(@PathVariable UserData user) {
return "User " + user.username() + " registered";
}

Solution

1. Step 1: Understand data binding for POST JSON

   To map JSON request body to a Java record, the parameter must be annotated with @RequestBody.

2. Step 2: Check each option

   @PostMapping("/register") public String registerUser(@RequestBody UserData user) { return "User " + user.username() + " registered with email " + user.email(); } correctly uses @RequestBody with UserData record and accesses its fields. @PostMapping("/register") public String registerUser(UserData user) { return "User " + user.username() + " registered"; } misses @RequestBody, so mapping fails. Options C and D use @RequestParam and @PathVariable which are for query/path parameters, not JSON body.

3. Final Answer:

   @PostMapping("/register") public String registerUser(@RequestBody UserData user) { return "User " + user.username() + " registered with email " + user.email(); } -> Option A

4. Quick Check:

   @RequestBody + record parameter = correct POST JSON mapping [OK]

Hint: Use @RequestBody with record to map JSON POST data [OK]

Common Mistakes:

• Omitting @RequestBody on complex objects
• Using @RequestParam or @PathVariable for JSON body
• Not accessing record fields correctly