How to Get JWT Token Value in Spring WebFlux

JSON Web Tokens (JWT) are a popular way to handle authentication and authorization in web applications. They are compact, self-contained, and can be easily passed between different parts of a system. In this article, we’ll look at how to get the value of a JWT token in a Spring WebFlux application.


A JWT is a JSON object that contains claims about an entity, such as a user. These claims can be encoded and signed, making them tamper-proof. JWTs are often used as a way to authenticate a user and authorize them to access certain resources.

In Spring WebFlux, JWTs can be used to authenticate and authorize requests. Spring WebFlux is a reactive web framework that allows for non-blocking, event-driven web applications. It handles HTTP requests asynchronously and can handle a large number of concurrent connections.

Understanding Spring WebFlux

Spring WebFlux is built on top of the Reactor library, which provides a reactive programming model for handling streams of data. In Spring WebFlux, requests are handled by WebFlux and RouterFunction classes. WebFlux is responsible for configuring the web application, while RouterFunction maps requests to handlers.

When a request is made to a Spring WebFlux application, it is handled by a RouterFunction. This function can check the request’s headers, including the JWT token, and determine if the request is authorized. If the request is authorized, it is passed to the appropriate handler. If the request is not authorized, the RouterFunction can return an error response.

Getting JWT Token Value in Spring WebFlux

To get the value of a JWT token in a Spring WebFlux application, you’ll need to do the following:

  1. Set up JWT token authentication
  2. Retrieve the JWT token value from the request header
  3. Decode and validate the JWT token
  4. Extract claims from the JWT token
  5. Handle errors and exceptions

Setting Up JWT Token Authentication

Before you can get the value of a JWT token, you’ll need to set up JWT token authentication in your Spring WebFlux application. This can be done by adding the spring-security-jwt dependency to your project and configuring it to use JWT token authentication.

Retrieving the JWT Token Value from the Request Header

Once JWT token authentication is set up, you can retrieve the JWT token value from the request header. This can be done by using the ServerRequest class, which provides access to the request’s headers.

String jwt = serverRequest.headers().header("Authorization").get(0);Code language: JavaScript (javascript)

Decoding and Validating the JWT Token

After you’ve retrieved the JWT token value, you’ll need to decode and validate it. This can be done using a JWT library, such as jjwt. You can use the Jwts.parser() method to create a JWT parser and the parseClaimsJws() method to parse the JWT token and extract the claims.

Claims claims = Jwts.parser()

Extracting Claims from the JWT Token

Once you’ve decoded and validated the JWT token, you can extract the claims from it. Claims are the information that is encoded in the JWT token, such as the user’s ID or the expiration time. You can use the get() method on the Claims object to get a specific claim by its key.

String userId = claims.get("userId", String.class);Code language: JavaScript (javascript)

Handling Errors and Exceptions

When working with JWT tokens, it’s important to handle errors and exceptions correctly. If the JWT token is invalid or expired, the parseClaimsJws() method will throw a SignatureException. You should catch this exception and return an appropriate error response to the client.

try {
    Claims claims = Jwts.parser()
} catch (SignatureException e) {
    return ServerResponse.status(401).build();
}Code language: JavaScript (javascript)


In this article, we’ve looked at how to get the value of a JWT token in a Spring WebFlux application. We’ve seen how to set up JWT token authentication, retrieve the JWT token value from the request header, decode and validate the JWT token, extract claims from the JWT token, and handle errors and exceptions. By following these steps, you can ensure that your Spring WebFlux application is secure and that only authorized users can access the resources they need.

For further learning on JWT tokens and Spring WebFlux, you can refer to the Spring Security JWT documentation and the Spring WebFlux documentation. Remember to keep your secret key safe and never share it with anyone.

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