PathVariable annotation

The `@PathVariable` annotation in Spring is used to extract values from the URI path of a request and bind them to method parameters in a controller. This is especially useful when you need to capture values from the URL itself, such as IDs or other parameters, which are often used to identify specific resources.

Example

• Step 1: Create a Spring Boot Application
  • Ensure you have the necessary dependencies in your `pom.xml` (for Maven) or `build.gradle` (for Gradle).

```xml
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
```

```groovy
implementation 'org.springframework.boot:spring-boot-starter-web'
```

• Step 2: Create the Main Application Class
  • Create the main class for the Spring Boot application.

```java
package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}
```

Explanation:

• `@SpringBootApplication`: Indicates a configuration class that declares one or more `@Bean` methods and also triggers auto-configuration and component scanning.

• Step 3: Create a Controller
  • Create a controller class that uses the `@PathVariable` annotation to handle incoming requests with path variables.

```java
package com.example.demo.controller;

import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api")
public class UserController {

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

    @GetMapping("/users/{id}/name/{name}")
    public String getUserByIdAndName(@PathVariable("id") Long userId, @PathVariable("name") String userName) {
        return "User ID: " + userId + ", Name: " + userName;
    }
}
```

Explanation:

• `@RestController`: Indicates that this class is a REST controller, and the return values of methods are directly written to the HTTP response body.
• `@RequestMapping(“/api”)`: Specifies that all methods in this class handle requests starting with `/api`.
• `@GetMapping(“/users/{id}”)`: Maps GET requests to `/api/users/{id}` to the `getUserById` method. `{id}` is a path variable that will be extracted from the URL.
• `@PathVariable(“id”)`: Binds the `{id}` path variable from the URL to the `userId` method parameter.
• `@GetMapping(“/users/{id}/name/{name}”)`: Maps GET requests to `/api/users/{id}/name/{name}` to the `getUserByIdAndName` method. `{id}` and `{name}` are path variables that will be extracted from the URL.
• `@PathVariable(“name”)`: Binds the `{name}` path variable from the URL to the `userName` method parameter.

• Step 4: Running the Application
  • Run the application from the main class (`DemoApplication`). You can test the endpoints using a tool like Postman or by navigating to the URLs in your browser:

• GET request to `http://localhost:8080/api/users/123` should return `”User ID: 123″`.
• GET request to `http://localhost:8080/api/users/123/name/John` should return `”User ID: 123, Name: John”`.

Conclusion

• `@PathVariable`: Used to extract values from the URI path and bind them to method parameters. It is useful for capturing dynamic values from the URL.
• Example: Demonstrated how to use `@PathVariable` to handle requests with path variables and extract them into method parameters.