Configure the Spring Boot Gateway

Oct 13, 2025 by wbrum.org 63 views

Introduction

When building a microservices architecture, it's common to use a gateway to route requests from clients to different services. In this scenario, we'll explore how to handle internal redirects when proxying a request from a Spring Boot Gateway to a Spring WebFlux application. We'll also discuss how to use Ngrok to expose our local application to the internet.

Problem Statement

Let's assume we have a Spring Boot Gateway application that proxies requests from clients to a Spring WebFlux application. The client sends a request to the gateway through Ngrok, which forwards the request to the local Spring WebFlux application. However, the Spring WebFlux application needs to redirect the user to a different URL, but the redirect URL is relative to the original request URL. This can cause issues when the redirect URL is not properly resolved.

Solution Overview

To solve this problem, we'll use the following approach:

Configure the Spring Boot Gateway: We'll configure the Spring Boot Gateway to proxy requests from clients to the Spring WebFlux application.
Use a Redirect Handler: We'll create a custom redirect handler in the Spring WebFlux application to handle internal redirects.
Use a Proxy Server: We'll use Ngrok to expose our local Spring WebFlux application to the internet.

Step 1: Configure the Spring Boot Gateway

First, let's configure the Spring Boot Gateway to proxy requests from clients to the Spring WebFlux application. We'll use the @EnableWebFluxSecurity annotation to enable WebFlux security and the @Bean annotation to create a RouteLocator bean that defines the routes.

import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebFluxSecurity;
import org.springframework.security.config.annotation.web.configurers.HttpSecurityConfigurerAdapter;
@Configuration
@EnableWebFluxSecurity
public class GatewayConfig {
@Bean
public RouteLocator myRouteLocator(RouteLocatorBuilder builder) {
    return builder.routes()
            .route(&quot;my_route&quot;, r -&gt; r.path(&quot;/my-path&quot;)
                    .uri(&quot;http://localhost:8080&quot;))
            .build();
}

}

Step 2: Create a Custom Redirect Handler

Next, let's create a custom redirect handler in the Spring WebFlux application to handle internal redirects. We'll use the @Bean annotation to create a ServerProperties bean that defines the server properties.

import org.springframework.boot.web.server.LocalServerPort;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.server.ServerProperties;
@Configuration
public class WebFluxConfig {
@Bean
public ServerProperties serverProperties() {
    return new ServerProperties();
}

}

Then, we'll create a custom redirect handler that uses the ServerProperties bean to resolve the redirect URL.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
@Component
public class RedirectHandler implements WebFilter {
private final ServerProperties serverProperties;

@Autowired
public RedirectHandler(ServerProperties serverProperties) {
    this.serverProperties = serverProperties;
}

@Override
public Mono&lt;Void&gt; filter(ServerWebExchange exchange, WebFilterChain chain) {
    // Resolve the redirect URL using the ServerProperties bean
    String redirectUrl = serverProperties.getRedirectUrl();

    // Create a new ServerWebExchange with the resolved redirect URL
    ServerWebExchange newExchange = exchange.mutate().request(exchange.getRequest().mutate().uri(URI.create(redirectUrl)).build()).build();

    // Continue the filter chain with the new ServerWebExchange
    return chain.filter(newExchange);
}

}

Step 3: Use a Proxy Server

Finally, let's use Ngrok to expose our local Spring WebFlux application to the internet. We'll use the ngrok command to start the proxy server.

ngrok http -host-header=rewrite --region=us http://localhost:8080

This will start the Ngrok proxy server and expose our local Spring WebFlux application to the internet.

Conclusion

In this article, we've explored how to handle internal redirects when proxying a request from a Spring Boot Gateway to a Spring WebFlux application. We've used a custom redirect handler to resolve the redirect URL and a proxy server to expose our local application to the internet. By following these steps, you can easily handle internal redirects in your Spring Boot Gateway application.

Example Use Case

Here's an example use case for the custom redirect handler:

Suppose we have a Spring WebFlux application that needs to redirect the user to a different URL after processing a request. The redirect URL is relative to the original request URL. We can use the custom redirect handler to resolve the redirect URL and create a new ServerWebExchange with the resolved redirect URL.

import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
@Component
public class RedirectHandler implements WebFilter {
@Override
public Mono&lt;Void&gt; filter(ServerWebExchange exchange, WebFilterChain chain) {
    // Resolve the redirect URL using the ServerProperties bean
    String redirectUrl = serverProperties.getRedirectUrl();

    // Create a new ServerWebExchange with the resolved redirect URL
    ServerWebExchange newExchange = exchange.mutate().request(exchange.getRequest().mutate().uri(URI.create(redirectUrl)).build()).build();

    // Continue the filter chain with the new ServerWebExchange
    return chain.filter(newExchange);
}

}

In this example, the custom redirect handler resolves the redirect URL using the ServerProperties bean and creates a new ServerWebExchange with the resolved redirect URL. This allows the Spring WebFlux application to redirect the user to the correct URL.

Benefits

The custom redirect handler provides several benefits, including:

Improved redirect handling: The custom redirect handler resolves the redirect URL using the ServerProperties bean, ensuring that the redirect URL is correctly resolved.
Simplified redirect logic: The custom redirect handler simplifies the redirect logic by creating a new ServerWebExchange with the resolved redirect URL.
Improved application scalability: The custom redirect handler improves application scalability by reducing the complexity of the redirect logic.

Conclusion

Introduction

In our previous article, we explored how to handle internal redirects when proxying a request from a Spring Boot Gateway to a Spring WebFlux application. We discussed how to use a custom redirect handler to resolve the redirect URL and a proxy server to expose our local application to the internet. In this article, we'll answer some frequently asked questions about internal redirects in Spring Boot Gateway applications.

Q: What is an internal redirect?

A: An internal redirect is a redirect that occurs within an application, where the redirect URL is relative to the original request URL. Internal redirects are commonly used in web applications to redirect users to a different page or URL after processing a request.

Q: Why do I need to handle internal redirects in my Spring Boot Gateway application?

A: You need to handle internal redirects in your Spring Boot Gateway application because the redirect URL may not be properly resolved when the redirect occurs. If the redirect URL is not properly resolved, the user may be redirected to an incorrect URL, which can cause issues with the application.

Q: How do I configure the Spring Boot Gateway to proxy requests from clients to the Spring WebFlux application?

A: To configure the Spring Boot Gateway to proxy requests from clients to the Spring WebFlux application, you need to use the @EnableWebFluxSecurity annotation to enable WebFlux security and the @Bean annotation to create a RouteLocator bean that defines the routes.

import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebFluxSecurity;
import org.springframework.security.config.annotation.web.configurers.HttpSecurityConfigurerAdapter;
@Configuration
@EnableWebFluxSecurity
public class GatewayConfig {
@Bean
public RouteLocator myRouteLocator(RouteLocatorBuilder builder) {
    return builder.routes()
            .route(&quot;my_route&quot;, r -&gt; r.path(&quot;/my-path&quot;)
                    .uri(&quot;http://localhost:8080&quot;))
            .build();
}

}

Q: How do I create a custom redirect handler in the Spring WebFlux application to handle internal redirects?

A: To create a custom redirect handler in the Spring WebFlux application to handle internal redirects, you need to use the @Bean annotation to create a ServerProperties bean that defines the server properties.

import org.springframework.boot.web.server.LocalServerPort;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.server.ServerProperties;
@Configuration
public class WebFluxConfig {
@Bean
public ServerProperties serverProperties() {
    return new ServerProperties();
}

}

Then, you need to create a custom redirect handler that uses the ServerProperties bean to resolve the redirect URL.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
@Component
public class RedirectHandler implements WebFilter {
private final ServerProperties serverProperties;

@Autowired
public RedirectHandler(ServerProperties serverProperties) {
    this.serverProperties = serverProperties;
}

@Override
public Mono&lt;Void&gt; filter(ServerWebExchange exchange, WebFilterChain chain) {
    // Resolve the redirect URL using the ServerProperties bean
    String redirectUrl = serverProperties.getRedirectUrl();

    // Create a new ServerWebExchange with the resolved redirect URL
    ServerWebExchange newExchange = exchange.mutate().request(exchange.getRequest().mutate().uri(URI.create(redirectUrl)).build()).build();

    // Continue the filter chain with the new ServerWebExchange
    return chain.filter(newExchange);
}

}

Q: How do I use a proxy server to expose my local Spring WebFlux application to the internet?

A: To use a proxy server to expose your local Spring WebFlux application to the internet, you need to use a tool like Ngrok to create a secure tunnel between your local application and the internet.

ngrok http -host-header=rewrite --region=us http://localhost:8080

This will start the Ngrok proxy server and expose your local Spring WebFlux application to the internet.

Q: What are the benefits of using a custom redirect handler in my Spring Boot Gateway application?

A: The benefits of using a custom redirect handler in your Spring Boot Gateway application include:

Improved redirect handling: The custom redirect handler resolves the redirect URL using the ServerProperties bean, ensuring that the redirect URL is correctly resolved.
Simplified redirect logic: The custom redirect handler simplifies the redirect logic by creating a new ServerWebExchange with the resolved redirect URL.
Improved application scalability: The custom redirect handler improves application scalability by reducing the complexity of the redirect logic.

Conclusion

In conclusion, internal redirects are a common issue in web applications, and handling them correctly is essential to ensure that users are redirected to the correct URL. By using a custom redirect handler in your Spring Boot Gateway application, you can improve redirect handling, simplify redirect logic, and improve application scalability.