BAEL-6086: Customize WebFlux Exceptions in Spring Boot 3 (#13948)

* BAEL-6086: Added code for webflux default and custom exception along with Unit Tests

* BAEL-6086: added missing import

* BAEL-6086: reformatting

* BAEL-6086: reformatted code

---------

Co-authored-by: balasr3 <balamurugan.radhakrishnan@imgarena.com>

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

@@ -20,7 +20,10 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-webflux</artifactId>
         </dependency>
-
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
         <dependency>
             <groupId>org.projectlombok</groupId>
             <artifactId>lombok</artifactId>
@@ -35,6 +38,11 @@
             <artifactId>reactor-test</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-test</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -42,8 +50,12 @@
             <plugin>
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-maven-plugin</artifactId>
+                <configuration>
+                    <mainClass>com.baeldung.spring.reactive.customexception.CustomExceptionApplication</mainClass>
+                    <layout>JAR</layout>
+                </configuration>
             </plugin>
         </plugins>
     </build>
 
-</project>
+</project>

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/CustomExceptionApplication.java

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

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/config/ErrorDetailsSerializer.java

@@ -0,0 +1,21 @@
+package com.baeldung.spring.reactive.customexception.config;
+
+import java.io.IOException;
+
+import com.baeldung.spring.reactive.customexception.model.ErrorDetails;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+
+public class ErrorDetailsSerializer extends JsonSerializer<ErrorDetails> {
+    @Override
+    public void serialize(ErrorDetails value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
+        gen.writeStartObject();
+        gen.writeStringField("code", value.getErrorCode()
+          .toString());
+        gen.writeStringField("message", value.getErrorMessage());
+        gen.writeStringField("reference", value.getReferenceUrl());
+        gen.writeEndObject();
+    }
+}
+

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/config/ProblemDetailsSerializer.java

@@ -0,0 +1,25 @@
+package com.baeldung.spring.reactive.customexception.config;
+
+import java.io.IOException;
+
+import org.springframework.http.ProblemDetail;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+
+public class ProblemDetailsSerializer extends JsonSerializer<ProblemDetail> {
+
+    @Override
+    public void serialize(ProblemDetail value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
+        gen.writeStartObject();
+        gen.writeObjectField("type", value.getType());
+        gen.writeObjectField("title", value.getTitle());
+        gen.writeObjectField("status", value.getStatus());
+        gen.writeObjectField("detail", value.getDetail());
+        gen.writeObjectField("instance", value.getInstance());
+        gen.writeObjectField("errors", value.getProperties().get("errors"));
+        gen.writeEndObject();
+    }
+}
+

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/controller/UserController.java

@@ -0,0 +1,57 @@
+package com.baeldung.spring.reactive.customexception.controller;
+
+import java.time.OffsetDateTime;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RestController;
+
+import com.baeldung.spring.reactive.customexception.exception.CustomErrorException;
+import com.baeldung.spring.reactive.customexception.exception.UserNotFoundException;
+import com.baeldung.spring.reactive.customexception.model.CustomErrorResponse;
+import com.baeldung.spring.reactive.customexception.model.ErrorDetails;
+import com.baeldung.spring.reactive.customexception.model.User;
+
+import reactor.core.publisher.Mono;
+
+@RestController
+public class UserController {
+
+    private Map<Long, User> userMap = new HashMap<>();
+
+    @GetMapping("/v1/users/{userId}")
+    public Mono<ResponseEntity<User>> getV1UserById(@PathVariable Long userId) {
+        return Mono.fromCallable(() -> {
+            User user = userMap.get(userId);
+            if (user == null) {
+                throw new UserNotFoundException("User not found with ID: " + userId);
+            }
+            return new ResponseEntity<>(user, HttpStatus.OK);
+        });
+    }
+
+    @GetMapping("/v2/users/{userId}")
+    public Mono<ResponseEntity<User>> getV2UserById(@PathVariable Long userId) {
+        return Mono.fromCallable(() -> {
+            User user = userMap.get(userId);
+            if (user == null) {
+                CustomErrorResponse customErrorResponse = CustomErrorResponse
+                  .builder()
+                  .traceId(UUID.randomUUID().toString())
+                  .timestamp(OffsetDateTime.now().now())
+                  .status(HttpStatus.NOT_FOUND)
+                  .errors(List.of(ErrorDetails.API_USER_NOT_FOUND))
+                  .build();
+                throw new CustomErrorException("User not found", customErrorResponse);
+            }
+            return new ResponseEntity<>(user, HttpStatus.OK);
+        });
+    }
+
+}

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/exception/CustomErrorException.java

@@ -0,0 +1,16 @@
+package com.baeldung.spring.reactive.customexception.exception;
+
+import com.baeldung.spring.reactive.customexception.model.CustomErrorResponse;
+
+import lombok.Getter;
+
+
+public class CustomErrorException extends RuntimeException {
+    @Getter
+    private CustomErrorResponse errorResponse;
+
+    public CustomErrorException(String message, CustomErrorResponse errorResponse) {
+        super(message);
+        this.errorResponse = errorResponse;
+    }
+}

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/exception/GlobalExceptionHandler.java

@@ -0,0 +1,34 @@
+package com.baeldung.spring.reactive.customexception.exception;
+
+import java.net.URI;
+import java.util.List;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ProblemDetail;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.reactive.result.method.annotation.ResponseEntityExceptionHandler;
+
+import com.baeldung.spring.reactive.customexception.model.CustomErrorResponse;
+import com.baeldung.spring.reactive.customexception.model.ErrorDetails;
+
+@RestControllerAdvice
+public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {
+    @ExceptionHandler(UserNotFoundException.class)
+    protected ProblemDetail handleNotFound(RuntimeException ex) {
+        ProblemDetail problemDetail = ProblemDetail.forStatusAndDetail(HttpStatus.NOT_FOUND, ex.getMessage());
+        problemDetail.setTitle("User not found");
+        problemDetail.setType(URI.create("https://example.com/problems/user-not-found"));
+        problemDetail.setProperty("errors", List.of(ErrorDetails.API_USER_NOT_FOUND));
+        return problemDetail;
+    }
+
+    @ExceptionHandler(CustomErrorException.class)
+    protected ResponseEntity<CustomErrorResponse> handleCustomError(RuntimeException ex) {
+        CustomErrorException customErrorException = (CustomErrorException) ex;
+        return ResponseEntity.status(customErrorException.getErrorResponse().getStatus())
+          .body(customErrorException.getErrorResponse());
+    }
+
+}

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/exception/UserNotFoundException.java

@@ -0,0 +1,9 @@
+package com.baeldung.spring.reactive.customexception.exception;
+
+public class UserNotFoundException extends RuntimeException {
+
+    public UserNotFoundException(String message) {
+        super(message);
+    }
+
+}

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/model/CustomErrorResponse.java

@@ -0,0 +1,22 @@
+package com.baeldung.spring.reactive.customexception.model;
+
+import java.time.OffsetDateTime;
+import java.util.List;
+
+import org.springframework.http.HttpStatus;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@Data
+@NoArgsConstructor
+@AllArgsConstructor
+@Builder
+public class CustomErrorResponse {
+    private String traceId;
+    private OffsetDateTime timestamp;
+    private HttpStatus status;
+    private List<ErrorDetails> errors;
+}

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/model/Error.java

@@ -0,0 +1,20 @@
+package com.baeldung.spring.reactive.customexception.model;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class Error {
+
+    private int code;
+
+    private String message;
+
+    protected String reference;
+
+}

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/model/ErrorDetails.java

@@ -0,0 +1,25 @@
+package com.baeldung.spring.reactive.customexception.model;
+
+
+import com.baeldung.spring.reactive.customexception.config.ErrorDetailsSerializer;
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+
+import lombok.Getter;
+
+@JsonSerialize(using = ErrorDetailsSerializer.class)
+public enum ErrorDetails {
+
+    API_USER_NOT_FOUND(123, "User not found", "http://example.com/123");
+    @Getter
+    private Integer errorCode;
+    @Getter
+    private String errorMessage;
+    @Getter
+    private String referenceUrl;
+
+    ErrorDetails(Integer errorCode, String errorMessage, String referenceUrl) {
+        this.errorCode = errorCode;
+        this.errorMessage = errorMessage;
+        this.referenceUrl = referenceUrl;
+    }
+}

spring-reactive-modules/spring-reactive-exceptions/src/main/java/com/baeldung/spring/reactive/customexception/model/User.java

@@ -0,0 +1,20 @@
+package com.baeldung.spring.reactive.customexception.model;
+
+import java.time.LocalDate;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class User {
+    private Long id;
+    private String firstName;
+    private String lastName;
+    private String email;
+    private LocalDate dateOfBirth;
+}

spring-reactive-modules/spring-reactive-exceptions/src/test/java/com/baeldung/spring/reactive/customexception/controller/UserControllerUnitTest.java

@@ -0,0 +1,84 @@
+package com.baeldung.spring.reactive.customexception.controller;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;
+
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.regex.Pattern;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.InjectMocks;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.http.ProblemDetail;
+import org.springframework.test.web.reactive.server.WebTestClient;
+
+import com.baeldung.spring.reactive.customexception.exception.GlobalExceptionHandler;
+import com.baeldung.spring.reactive.customexception.model.ErrorDetails;
+
+@SpringBootTest(webEnvironment = RANDOM_PORT)
+class UserControllerUnitTest {
+
+    @Autowired
+    private WebTestClient webClient;
+
+    @InjectMocks
+    private UserController userController;
+
+    @Autowired
+    private GlobalExceptionHandler globalExceptionHandler;
+
+    @BeforeEach
+    void setupTests() {
+        // Given
+        webClient = WebTestClient.bindToController(userController)
+          .controllerAdvice(globalExceptionHandler)
+          .configureClient()
+          .build();
+    }
+
+    @Test
+    void givenGetUserV1Endpoint_whenHitWithInvalidUser_thenResponseShouldContainProblemDetailWithCustomAttributes() throws Exception {
+        // When
+        ProblemDetail problemDetail = webClient.get()
+          .uri("/v1/users/123")
+          .exchange()
+          .expectStatus()
+          .isNotFound()
+          .expectBody(ProblemDetail.class)
+          .returnResult()
+          .getResponseBody();
+        // Then
+        assertNotNull(problemDetail);
+        assertNotNull(problemDetail.getProperties().get("errors"));
+        List<LinkedHashMap> errors = (List<LinkedHashMap>) problemDetail.getProperties().get("errors");
+        assertEquals(ErrorDetails.API_USER_NOT_FOUND.getErrorCode().toString(),
+          errors.get(0).get("code"));
+        assertEquals(ErrorDetails.API_USER_NOT_FOUND.getErrorMessage().toString(),
+          errors.get(0).get("message"));
+        assertEquals(ErrorDetails.API_USER_NOT_FOUND.getReferenceUrl().toString(),
+          errors.get(0).get("reference"));
+    }
+
+    @Test
+    void givenGetUserV2Endpoint_whenHitWithInvalidUser_thenResponseShouldContainCustomException() throws Exception {
+        // When
+        String regex = "^\\{\\s*\"traceId\":\\s*\"[^\"]*\",\\s*\"timestamp\":\\d+\\.\\d+,\\s*\"status\":\\s*\"[^\"]*\",\\s*\"errors\":\\s*\\[\\s*\\{\\s*\"code\":\\s*\"[^\"]*\",\\s*\"message\":\\s*\"[^\"]*\",\\s*\"reference\":\\s*\"[^\"]*\"\\s*\\}\\s*\\]\\s*\\}$";
+        Pattern errorResponseSampleFormat = Pattern.compile(regex);
+        String errorResponse = webClient.get()
+          .uri("/v2/users/123")
+          .exchange()
+          .expectStatus()
+          .isNotFound()
+          .expectBody(String.class)
+          .returnResult()
+          .getResponseBody();
+        // Then
+        assertTrue(errorResponseSampleFormat.matcher(errorResponse).matches());
+    }
+
+}