[BAEL-7546] - How to intercept a request and add headers in WebFlux (#16291)

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* Added the Implementation Code.

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* Added the JUnit Tests.

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* Updated parent module with the new module reference.

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* CICD Build Fix for PMD Violation

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* CICD Build Fix for PMD Violation

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* Use four space indents in the pom file.

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* Use 2 space indents line continuation.

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* Add test case for Unmodifiable Header map scenario.

* [BAEL-7546] - How to intercept a request and add headers in WebFlux
* Indentation fixes.

spring-reactive-modules/pom.xml

@@ -20,6 +20,7 @@
         <module>spring-reactive-data</module>
         <module>spring-reactive-2</module>
         <module>spring-reactive-3</module>
+        <module>spring-reactive-4</module>
         <module>spring-reactive-client</module>
         <module>spring-reactive-client-2</module>
         <module>spring-reactive-filters</module>

spring-reactive-modules/spring-reactive-4/pom.xml

@@ -0,0 +1,53 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>spring-reactive-4</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>spring-reactive-4</name>
+    <packaging>jar</packaging>
+    <description>spring sample project about new features</description>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-boot-3</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-boot-3</relativePath>
+    </parent>
+
+    <properties>
+        <wiremock-standalone.version>3.4.2</wiremock-standalone.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-webflux</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty-all</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.wiremock</groupId>
+            <artifactId>wiremock-standalone</artifactId>
+            <version>${wiremock-standalone.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/SpringReactiveApplication.java

@@ -0,0 +1,13 @@
+package com.baeldung;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SpringReactiveApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(SpringReactiveApplication.class, args);
+    }
+
+}

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/controller/TraceController.java

@@ -0,0 +1,21 @@
+package com.baeldung.controller;
+
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestHeader;
+import org.springframework.web.bind.annotation.RestController;
+
+import reactor.core.publisher.Mono;
+
+@RestController
+public class TraceController {
+
+    @GetMapping(value = "/trace-annotated")
+    public Mono<String> trace(@RequestHeader(name = "traceId") final String traceId) {
+        return Mono.just("TraceId: ".concat(traceId));
+    }
+
+    @GetMapping(value = "/trace-exceptional")
+    public Mono<String> traceExceptional() {
+        return Mono.just("Traced");
+    }
+}

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/filters/ExceptionalTraceFilter.java

@@ -0,0 +1,25 @@
+package com.baeldung.filters;
+
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilter;
+import org.springframework.web.server.WebFilterChain;
+
+import reactor.core.publisher.Mono;
+
+@Component
+public class ExceptionalTraceFilter implements WebFilter {
+
+    @Override
+    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+        if (exchange.getRequest()
+            .getPath()
+            .toString()
+            .equals("/trace-exceptional")) {
+            exchange.getRequest()
+                .getHeaders()
+                .add("traceId", "TRACE-ID");
+        }
+        return chain.filter(exchange);
+    }
+}

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/filters/TraceHandlerFilterFunction.java

@@ -0,0 +1,20 @@
+package com.baeldung.filters;
+
+import org.springframework.web.reactive.function.server.HandlerFilterFunction;
+import org.springframework.web.reactive.function.server.HandlerFunction;
+import org.springframework.web.reactive.function.server.ServerRequest;
+import org.springframework.web.reactive.function.server.ServerResponse;
+
+import reactor.core.publisher.Mono;
+
+public class TraceHandlerFilterFunction implements HandlerFilterFunction<ServerResponse, ServerResponse> {
+
+    @Override
+    public Mono<ServerResponse> filter(ServerRequest request, HandlerFunction<ServerResponse> handlerFunction) {
+
+        ServerRequest serverRequest = ServerRequest.from(request)
+            .header("traceId", "FUNCTIONAL-TRACE-ID")
+            .build();
+        return handlerFunction.handle(serverRequest);
+    }
+}

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/filters/TraceWebFilter.java

@@ -0,0 +1,20 @@
+package com.baeldung.filters;
+
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.WebFilter;
+import org.springframework.web.server.WebFilterChain;
+
+import reactor.core.publisher.Mono;
+
+@Component
+public class TraceWebFilter implements WebFilter {
+
+    @Override
+    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
+        exchange.getRequest()
+            .mutate()
+            .header("traceId", "ANNOTATED-TRACE-ID");
+        return chain.filter(exchange);
+    }
+}

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/filters/WebClientFilters.java

@@ -0,0 +1,18 @@
+package com.baeldung.filters;
+
+import org.springframework.util.MultiValueMap;
+import org.springframework.web.reactive.function.client.ClientRequest;
+import org.springframework.web.reactive.function.client.ExchangeFilterFunction;
+
+public final class WebClientFilters {
+
+    public static ExchangeFilterFunction modifyRequestHeaders(final MultiValueMap<String, String> changedMap) {
+        return (request, next) -> {
+            final ClientRequest clientRequest = ClientRequest.from(request)
+                .header("traceId", "TRACE-ID")
+                .build();
+            changedMap.addAll(clientRequest.headers());
+            return next.exchange(clientRequest);
+        };
+    }
+}

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/handler/TraceRouterHandler.java

@@ -0,0 +1,22 @@
+package com.baeldung.handler;
+
+import org.springframework.stereotype.Component;
+import org.springframework.web.reactive.function.server.ServerRequest;
+import org.springframework.web.reactive.function.server.ServerResponse;
+
+import reactor.core.publisher.Mono;
+
+import static org.springframework.web.reactive.function.server.ServerResponse.ok;
+
+@Component
+public class TraceRouterHandler {
+
+    public Mono<ServerResponse> handle(final ServerRequest serverRequest) {
+
+        final String traceId = serverRequest.headers()
+            .firstHeader("traceId");
+        assert traceId != null;
+        final Mono<String> body = Mono.just("TraceId: ".concat(traceId));
+        return ok().body(body, String.class);
+    }
+}

spring-reactive-modules/spring-reactive-4/src/main/java/com/baeldung/router/TraceRouter.java

@@ -0,0 +1,27 @@
+package com.baeldung.router;
+
+import com.baeldung.filters.TraceHandlerFilterFunction;
+import com.baeldung.handler.TraceRouterHandler;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.reactive.function.server.RouterFunction;
+import org.springframework.web.reactive.function.server.ServerRequest;
+import org.springframework.web.reactive.function.server.ServerResponse;
+
+import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
+import static org.springframework.web.reactive.function.server.RouterFunctions.route;
+
+@Configuration
+public class TraceRouter {
+
+    @Bean
+    public RouterFunction<ServerResponse> routes(TraceRouterHandler routerHandler) {
+        return route(GET("/trace-functional-filter"), routerHandler::handle).filter(new TraceHandlerFilterFunction())
+            .and(route().GET("/trace-functional-before", routerHandler::handle)
+                .before(request -> ServerRequest.from(request)
+                    .header("traceId", "FUNCTIONAL-TRACE-ID")
+                    .build())
+                .build());
+    }
+}

spring-reactive-modules/spring-reactive-4/src/main/resources/logback.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT"/>
+    </root>
+</configuration>

spring-reactive-modules/spring-reactive-4/src/test/java/com/baeldung/controller/TraceControllerIntegrationTest.java

@@ -0,0 +1,50 @@
+package com.baeldung.controller;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import org.springframework.test.web.reactive.server.EntityExchangeResult;
+import org.springframework.test.web.reactive.server.WebTestClient;
+
+@ExtendWith(SpringExtension.class)
+@WebFluxTest(controllers = TraceController.class)
+public class TraceControllerIntegrationTest {
+
+    @Autowired
+    private WebTestClient webTestClient;
+
+    @Test
+    void whenCallTraceAnnotatedEndpoint_thenResponseContainsTraceId() {
+        EntityExchangeResult<String> result = webTestClient.get()
+            .uri("/trace-annotated")
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody(String.class)
+            .returnResult();
+
+        final String body = "TraceId: ANNOTATED-TRACE-ID";
+        assertEquals(result.getResponseBody(), body);
+
+    }
+
+    @Test
+    void whenCallTraceExceptionalEndpoint_thenThrowsException() {
+        EntityExchangeResult<Map> result = webTestClient.get()
+            .uri("/trace-exceptional")
+            .exchange()
+            .expectStatus()
+            .is5xxServerError()
+            .expectBody(Map.class)
+            .returnResult();
+
+        assertNotNull(result.getResponseBody());
+    }
+}

spring-reactive-modules/spring-reactive-4/src/test/java/com/baeldung/filters/WebClientFilterUnitTest.java

@@ -0,0 +1,55 @@
+package com.baeldung.filters;
+
+import static com.baeldung.filters.WebClientFilters.modifyRequestHeaders;
+import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
+import static com.github.tomakehurst.wiremock.client.WireMock.get;
+import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.wireMockConfig;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
+import org.springframework.web.reactive.function.client.WebClient;
+
+import com.github.tomakehurst.wiremock.junit5.WireMockExtension;
+import com.github.tomakehurst.wiremock.junit5.WireMockTest;
+
+@WireMockTest
+public class WebClientFilterUnitTest {
+
+    @RegisterExtension
+    static WireMockExtension extension = WireMockExtension.newInstance()
+        .options(wireMockConfig().dynamicPort()
+            .dynamicHttpsPort())
+        .build();
+
+    @Test
+    void whenCallEndpoint_thenRequestHeadersModified() {
+        extension.stubFor(get("/test").willReturn(aResponse().withStatus(200)
+            .withBody("SUCCESS")));
+
+        final MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
+
+        WebClient webClient = WebClient.builder()
+            .filter(modifyRequestHeaders(map))
+            .build();
+        String actual = sendGetRequest(webClient);
+
+        final String body = "SUCCESS";
+        Assertions.assertEquals(actual, body);
+        Assertions.assertEquals("TRACE-ID", map.getFirst("traceId"));
+    }
+
+    private String sendGetRequest(final WebClient webClient) {
+        return webClient.get()
+            .uri(getUrl())
+            .retrieve()
+            .bodyToMono(String.class)
+            .block();
+    }
+
+    private String getUrl() {
+        return "http://localhost:" + extension.getPort() + "/test";
+    }
+}

spring-reactive-modules/spring-reactive-4/src/test/java/com/baeldung/handler/TraceRouteHandlerIntegrationTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.handler;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
+import org.springframework.context.ApplicationContext;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import org.springframework.test.web.reactive.server.EntityExchangeResult;
+import org.springframework.test.web.reactive.server.WebTestClient;
+
+import com.baeldung.router.TraceRouter;
+
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration(classes = { TraceRouter.class, TraceRouterHandler.class })
+@WebFluxTest
+public class TraceRouteHandlerIntegrationTest {
+
+    @Autowired
+    private ApplicationContext context;
+    private WebTestClient webTestClient;
+
+    @BeforeEach
+    void setUp() {
+        webTestClient = WebTestClient.bindToApplicationContext(context)
+            .build();
+    }
+
+    @Test
+    void whenCallTraceFunctionalFilterEndpoint_thenResponseContainsTraceId() {
+        EntityExchangeResult<String> result = webTestClient.get()
+            .uri("/trace-functional-filter")
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody(String.class)
+            .returnResult();
+
+        final String body = "TraceId: FUNCTIONAL-TRACE-ID";
+        assertEquals(result.getResponseBody(), body);
+    }
+
+    @Test
+    void whenCallTraceFunctionalBeforeEndpoint_thenResponseContainsTraceId() {
+        EntityExchangeResult<String> result = webTestClient.get()
+            .uri("/trace-functional-before")
+            .exchange()
+            .expectStatus()
+            .isOk()
+            .expectBody(String.class)
+            .returnResult();
+
+        final String body = "TraceId: FUNCTIONAL-TRACE-ID";
+        assertEquals(result.getResponseBody(), body);
+    }
+}