diff --git a/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/ex/NotFoundException.java b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/ex/NotFoundException.java
new file mode 100644
index 0000000000..5401a4d133
--- /dev/null
+++ b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/ex/NotFoundException.java
@@ -0,0 +1,12 @@
+package com.baeldung.webflux.exceptionhandeling.ex;
+
+public class NotFoundException extends RuntimeException {
+
+    public NotFoundException(String message) {
+        super(message);
+    }
+
+    public NotFoundException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}
diff --git a/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/model/User.java b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/model/User.java
new file mode 100644
index 0000000000..6bc39da062
--- /dev/null
+++ b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/model/User.java
@@ -0,0 +1,29 @@
+package com.baeldung.webflux.exceptionhandeling.model;
+
+public class User {
+    private String id;
+    private String username;
+
+    public String getId() {
+        return id;
+    }
+
+    public void setId(String id) {
+        this.id = id;
+    }
+
+    public String getUsername() {
+        return username;
+    }
+
+    public void setUsername(String username) {
+        this.username = username;
+    }
+
+    public User(String userId, String userName) {
+        this.id = userId;
+        this.username = userName;
+
+    }
+}
+
diff --git a/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/repository/UserRepository.java b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/repository/UserRepository.java
new file mode 100644
index 0000000000..8c153aa2e6
--- /dev/null
+++ b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/repository/UserRepository.java
@@ -0,0 +1,22 @@
+package com.baeldung.webflux.exceptionhandeling.repository;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.springframework.stereotype.Repository;
+
+import com.baeldung.webflux.exceptionhandeling.model.User;
+
+@Repository
+public class UserRepository {
+    private final Map<String, User> userDatabase = new ConcurrentHashMap<>();
+
+    public UserRepository() {
+        userDatabase.put("1", new User("1", "John Doe"));
+        userDatabase.put("2", new User("2", "Jane Smith"));
+    }
+
+    public User findById(String id) {
+        return userDatabase.get(id);
+    }
+}
diff --git a/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/service/UserService.java b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/service/UserService.java
new file mode 100644
index 0000000000..da5a672183
--- /dev/null
+++ b/spring-5-webflux-2/src/main/java/com/baeldung/webflux/exceptionhandeling/service/UserService.java
@@ -0,0 +1,34 @@
+package com.baeldung.webflux.exceptionhandeling.service;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+
+import com.baeldung.webflux.exceptionhandeling.ex.NotFoundException;
+import com.baeldung.webflux.exceptionhandeling.model.User;
+import com.baeldung.webflux.exceptionhandeling.repository.UserRepository;
+
+import reactor.core.publisher.Mono;
+
+public class UserService {
+
+    private final UserRepository userRepository;
+
+    @Autowired
+    public UserService(UserRepository userRepository) {
+        this.userRepository = userRepository;
+    }
+
+    public Mono<User> getUserByIdThrowingException(String id) {
+        User user = userRepository.findById(id);
+        if (user == null)
+          throw new NotFoundException("User Not Found");
+        return Mono.justOrEmpty(user);
+    }
+
+    public Mono<User> getUserByIdUsingMonoError(String id) {
+        User user = userRepository.findById(id);
+        return (user != null) ? Mono.justOrEmpty(user) : Mono.error(new NotFoundException("User Not Found"));
+
+    }
+}
diff --git a/spring-5-webflux-2/src/test/java/com/baeldung/webflux/exceptionhandeling/UserControllerUnitTest.java b/spring-5-webflux-2/src/test/java/com/baeldung/webflux/exceptionhandeling/UserControllerUnitTest.java
new file mode 100644
index 0000000000..e968cfeea3
--- /dev/null
+++ b/spring-5-webflux-2/src/test/java/com/baeldung/webflux/exceptionhandeling/UserControllerUnitTest.java
@@ -0,0 +1,36 @@
+package com.baeldung.webflux.exceptionhandeling;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import org.junit.jupiter.api.Test;
+
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import com.baeldung.webflux.exceptionhandeling.ex.NotFoundException;
+import com.baeldung.webflux.exceptionhandeling.model.User;
+import com.baeldung.webflux.exceptionhandeling.service.UserService;
+import com.baeldung.webflux.exceptionhandeling.repository.UserRepository;
+
+public class UserControllerUnitTest {
+    UserRepository repositoryMock = mock(UserRepository.class);
+    private final UserService userService = new UserService(repositoryMock);
+
+    @Test
+    public void givenNonExistUser_whenFailureCall_then_Throws_exception() {
+        assertThrows(NotFoundException.class, () -> userService.getUserByIdThrowingException("3"));
+
+    }
+
+    @Test
+    public void givenNonExistUser_whenFailureCall_then_returnMonoError() {
+        Mono<User> result = userService.getUserByIdUsingMonoError("3");
+        StepVerifier.create(result)
+          .expectError(NotFoundException.class)
+          .verify();
+
+    }
+
+}