Difference between @RequestParam and @PathVariable in Spring MVC

Hello guys, if you are wondering what is difference between @ReqestParam and @PathVaraible annotation in Spring MVC, most likely because it was asked to you on a Java and Spring interview or maybe you are just curious then you have come to the right place. In the past, I have talked about difference between @Component, @Service, @Reposistory and @Controller annotations and in this comprehensive article we are going to take an in-depth look at the difference between the two most frequently used annotations in Spring MVC. It provides two commonly used annotations, namely @RequestParam and @PathVariable, which play a significant role in parameter handling within web applications. 

Although both annotations facilitate data extraction from requests, they serve distinct purposes. This comprehensive article aims to thoroughly explore the functionalities, use cases, and key disparities between @RequestParam and @PathVariable annotations.

By gaining a profound understanding of these annotations, developers can effectively leverage their capabilities to manage user input in Spring MVC applications. But, before we analyze the differences between these two annotations, let first understand them in bit more details. This will later help you to understand their differences as well. 




What is  @RequestParam Annotation in Spring MVC? Where does it is used?

The @RequestParam annotation is used to bind individual query parameters from the request URL to method parameters in a controller. It is primarily used to extract values from the query string or the form data of an HTTP request. 

Let's consider an example to better understand its usage:

@GetMapping("/user")

public String getUser(@RequestParam("id") int userId) {

// Logic to fetch user details based on the provided ID

// ...

}




In the above example, the @RequestParam("id") annotation is used to bind the value of the "id" query parameter from the request URL to the userId method parameter. For instance, if the URL is "/user?id=786", the value 786 will be assigned to the userId variable.


@GetMapping("/user")

public String getUser(@RequestParam(defaultValue = “10”, required=true) int userId) {

// Logic to fetch user details based on the provided ID

// ...

}



defaultValue – If the request doesn't contain a value or is empty, defaultValue serves as a fallback mechanism.

name – parameter name

required – It is just like a flag, if it is set to true, a missing parameter will yield an error.

value – This is the name attributes' alias.




Key points about @RequestParam annotation:

• It is used for binding query parameters.

• It is suitable for optional parameters, as the parameter value can be omitted.

• The parameter name in the annotation should match the name of the query parameter.

• It supports additional features such as default values and parameter mapping.


Here is also a nice diagram which explains how Request is handled in a Spring MVC application:




2. What is @PathVariable Annotation? Where does it is used?


The @PathVariable annotation is used to extract data from the URI template in the request URL. It is mainly utilized to capture dynamic values from the URL path itself. 

Let's consider the following example: 

@GetMapping("/users/{id}")

public String getUserById(@PathVariable("id") int userId) {

// Logic to fetch user details based on the provided ID

// ...

}


In the above code snippet, the @PathVariable("id") annotation is used to bind the value of the "id" path variable from the request URL to the userId method parameter. For instance, if the URL is "/users/786", the value 786 will get assigned to the variable userId.

Key points about @PathVariable annotation:

• It is used for binding path variables from the URL.

• It is suitable for mandatory parameters, as the parameter value must be present.

• The parameter name in the annotation should match the name of the path variable in the URL.

• It supports additional features such as regular expression constraints.




Differences between @RequestParam and @PathVariable?

Now that you have seen and understood what is @RequestParam and what is @PathVariable annotation and also understand their usage, let's see the difference between two of them:


1. Purpose

@RequestParam extracts query parameters from the request URL or form data.

@PathVariable extracts dynamic values from the URL path.




2. Binding

@RequestParam binds parameters by name from the query string or form data.

@PathVariable binds parameters by name from the URL path.




3. Parameter Presence

The @RequestParam supports optional parameters, as the absence of a parameter will result in a default value or null.

@PathVariable requires the parameter to be present in the URL path. It is not optional.




4. Naming

@RequestParam uses the name attribute in the annotation to specify the parameter name.

@PathVariable uses the name attribute in the annotation to specify the path variable name.


These are the key differences between @RequestParam and @PathVaraible annotations in Spring MVC and you should remember these point not just while answering during interviews but also during coding Spring boot applications. 

If you need more differences, here is a nice table which highlights the difference between @RequestParam and @PathVariable in Java:




An Example of @RequestParam and @PathVariable Annotations in Java

Let’s understand with the difference with the help of an example program. It will showcases the usage of both @RequestParam and @PathVariable annotations in a Spring MVC application.



// UserController.java


@Controller

@RequestMapping("/user")

public class UserController {



@GetMapping("/info")

public String getUserInfo(@RequestParam("id") int userId, Model model) {

// Logic to fetch user details based on the provided ID

User user = userService.getUserById(userId);



model.addAttribute("user", user);



return "user-info";

}



@GetMapping("/profile/{username}")

public String getUserProfile(@PathVariable("username") String username, Model model) {

// Logic to fetch user details based on the provided username

User user = userService.getUserByUsername(username);



model.addAttribute("user", user);



return "user-profile";

}



// Other controller methods and dependencies...

}



The getUserInfo() method:

This method is mapped to the "/info" endpoint relative to the "/user" base URL.

The Model parameter allows us to add the retrieved user details to the model for rendering in the view.

The method fetches the user details based on the provided userId using a userService (assumed to be defined as a dependency).

The retrieved User object is added to the model using model.addAttribute().

Finally, the method returns the logical view name "user-info", which will be resolved by the view resolver configured in the application.


The getUserProfile() method:

This method is mapped to the "/profile/{username}" endpoint relative to the "/user" base URL.

The @PathVariable("username") annotation is used to bind the value of the "username" path variable from the request URL to the username method parameter.

The Model parameter allows us to add the retrieved user details to the model for rendering in the view.

The method fetches the user details based on the provided username using a userService.

The retrieved User object is added to the model using model.addAttribute().

Finally, the method returns the logical view name "user-profile", which will be resolved by the view resolver configured in the application.

These methods demonstrate how the @RequestParam annotation is used to extract query parameters (id in the first example), while the @PathVariable annotation is used to capture path variables (username in the second example). The extracted parameters are then used to fetch user details and pass them to the corresponding views.


Note: The code snippet assumes the existence of a User class and a userService dependency that provides methods to retrieve user information.

By using @RequestParam and @PathVariable annotations, developers can effectively handle different types of parameters in their Spring MVC applications, providing flexible and robust request handling capabilities.



That's all about the difference between @RequestParam and @PathVariable in Spring MVC. Understanding the difference between @RequestParam and @PathVariable annotations is crucial when developing Spring MVC applications. While @RequestParam deals with query parameters and form data, @PathVariable focuses on extracting dynamic values from the URL path. 

By using the appropriate annotation based on the requirements, developers can effectively handle and process user input in their applications.

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