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Spring Webflux change from Netty to Tomcat embedded server

I have changed the pom to switch from Netty to Tomcat as below, but now I get : java.lang.IllegalStateException: No suitable default ClientHttpConnector found, why is that? With Netty before the change was all good.
<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.7.5</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.fer</groupId>
<artifactId>DemoReactive</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>DemoReactive</name>
<description>Demo project for Reactive</description>
<properties>
<java.version>11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
<exclusions>
<exclusion>
<artifactId>spring-boot-starter-reactor-netty</artifactId>
<groupId>org.springframework.boot</groupId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</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>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>

Netty is optimal for Webflux. Don't replace it. The basic principle of operation of the two systems is different. If you want to use Tomcat, use the spring-boot-starter-web dependency, not webflux.
Spring webFlux differrences when Netty vs Tomcat is used under the hood
Spring Web MVC vs Spring WebFlux. Blocking and Non-blocking
Non-blocking programming requires a different approach because you must not block any thread. But you can use a blocker mechanism it just be wrapped.
https://projectreactor.io/docs/core/release/reference/#faq.wrap-blocking
If you want to program like with spring-boot-starter-web pack, not as "stream". I recommend using the Kotlin language with Coroutine, which is two-way compatible with ProjectReactor and Java.
And you can't use thread-based data like Tomcat because more processes can use one thread so there may be thread data that another process can override.
https://projectreactor.io/docs/core/release/reference/#context

I believe this is how you would do something equivalent, note the difference in exclusion:
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>my-webflux-app</artifactId>
<version>1.0.0</version>
<properties>
<java.version>11</java.version>
<spring-boot.version>2.3.3.RELEASE</spring-boot.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
<exclusions>
<exclusion>
<groupId>io.netty</groupId>
<artifactId>netty-all</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>

Spring Maven: Correct the classpath of you application

I am getting the following error when trying to run my spring project:
Description:
An attempt was made to call a method that does not exist. The attempt was made from the following location:
org.hibernate.cfg.annotations.EntityBinder.processComplementaryTableDefinitions(EntityBinder.java:1236)
The following method did not exist:
'javax.persistence.Index[] javax.persistence.Table.indexes()'
The calling method's class, org.hibernate.cfg.annotations.EntityBinder, was loaded from the following location:
jar:file:/C:/Users/bobal/.m2/repository/org/hibernate/hibernate-core/5.4.14.Final/hibernate-core-5.4.14.Final.jar!/org/hibernate/cfg/annotations/EntityBinder.class
The called method's class, javax.persistence.Table, is available from the following locations:
jar:file:/C:/Users/bobal/Documents/Java%20Projects/restService/lib/javax.persistence.jar!/javax/persistence/Table.class
jar:file:/C:/Users/bobal/.m2/repository/jakarta/persistence/jakarta.persistence-api/2.2.3/jakarta.persistence-api-2.2.3.jar!/javax/persistence/Table.class
jar:file:/C:/Users/bobal/.m2/repository/org/hibernate/javax/persistence/hibernate-jpa-2.1-api/1.0.0.Final/hibernate-jpa-2.1-api-1.0.0.Final.jar!/javax/persistence/Table.class
The called method's class hierarchy was loaded from the following locations:
javax.persistence.Table: file:/C:/Users/bobal/Documents/Java%20Projects/restService/lib/javax.persistence.jar
Action:
Correct the classpath of your application so that it contains compatible versions of the classes org.hibernate.cfg.annotations.EntityBinder and javax.persistence.Table
Process finished with exit code 1
I think that this error may be due to having conflicting versions of some dependencies, but I'm not very sure. This is my first ever Spring project.
Here is my UPDATED pom.xml file
<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.6.2</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>restService</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>restService</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>11</java.version>
<jdbc.version>8.2.2.jre11</jdbc.version>
<hibernate.version>5.4.14.Final</hibernate.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.jetbrains</groupId>
<artifactId>annotations</artifactId>
<version>17.0.0</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.8</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>com.microsoft.sqlserver</groupId>
<artifactId>mssql-jdbc</artifactId>
<version>${jdbc.version}</version>
</dependency>
<dependency>
<groupId>org.hibernate.validator</groupId>
<artifactId>hibernate-validator</artifactId>
<version>${hibernate-validator.version}</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-jpa</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
If you find anything wrong please feel free to point it out and explain why. Trying to learn as much as I can.

You have multiple version of JPA libraries, that's why you are getting this error.
jakarta.persistence-api-2.2.3.jar and
hibernate-jpa-2.1-api-1.0.0.Final.jar
You can remove hibernate-jpa-2.1-api-1.0.0.Final.jar dependency because it is also present in jakarta.persistence-api-2.2.3.jar.

Maven - Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:2.4.1:run

I created my project at https://start.spring.io/
Several errors on the internet are similar but did not solve my problem.
when executing it I found an error return:
Failed to execute goal org.springframework.boot: spring-boot-maven-plugin: 2.4.1: run
Here are my POM and main file main
POM:
<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.4.1</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>net.javaguides</groupId>
<artifactId>spring-boot-restfull-webservice</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring-boot-restfull-webservice</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
Class:
package net.javaguides.springboot;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
#SpringBootApplication
public class SpringBootRestfullWebserviceApplication {
public static void main(String[] args) {
SpringApplication.run(SpringBootRestfullWebserviceApplication.class, args);
}
}
I'm new to Springboot, how do I fix it?

I've gotten your build to work, but I had to make some compromises.
I looked at the Spring documentation for what you are trying:
https://spring.io/guides/gs/rest-service/
Then I looked at the pom.xml for the example:
https://github.com/spring-guides/gs-rest-service/blob/master/complete/pom.xml
Despite the fact that the documentation says you can use Java 1.8 or higher, you need to use 1.8. If you go higher, you have to specify the property encoding in the plugin, and you can't do that because you are using the Spring Boot plugin rather than a plugin you can configure in the pom.xml for your project.
I also added a lower version of the maven-surefire-plugin than Spring Boot uses. With this version, you get the error [ERROR] There are test failures, but you are not running any tests.
I commented out the MySql and JPA dependencies, which won't work unless you have database connection settings.
<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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.4.1</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>net.javaguides</groupId>
<artifactId>spring-boot-restful-webservice</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring-boot-restful-webservice</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<!--
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!--
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.5</version>
<configuration>
<skipTests>false</skipTests>
<testFailureIgnore>true</testFailureIgnore>
<forkMode>once</forkMode>
</configuration>
</plugin>
</plugins>
</build>
</project>

In my case i was running the jar file when i was activated maven install. The made it unable to delete and create a new jar as one was already running. After i quit running the jar file. I was able to build the project. sometimes reading error messages helps

Try to read well the exception log in cli, after executing your "mvn spring-boot:run" command.
It can be a due to
a connection with your DB, for example mysql not started
Or started but the DB name is not correct in your application.properties file e.g. java.sql.SQLSyntaxErrorException: Unknown database
Or even the password used of the db user is not correct in the application.properties file: e.g Caused by: java.sql.SQLNonTransientConnectionException: Public Key Retrieval is not allowed
so analyze first your logs before modifying java version, xml elements in the plugin ...
Normally this follwing generic pom.xml is enough to have maven running successfully your tomcat server (embedded in spring boot):
<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.7.2</version>
<relativePath />
</parent>
<groupId>com.example</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>17</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>

Whitelabel Error Page instead of specific jsp page

I have seen several Questions about this problem and I haven't solved this problem yet:
I have checked them:
Springboot Whitelabel Error Page --- my controller is found and registered by spring.
Spring boot - Whitelabel Error Page --- my controller is annotated with #Controller and I return string which matches the jsp file name I want to see.
This is my pom.xml file:
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.1.RELEASE</version>
<relativePath /> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>test</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<name>demo</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
This is application.properties file:
server.port=8088
spring.mvc.view.prefix=/WEB-INF/views/
spring.mvc.view.suffix=.jsp
This is folder structure:

You have need to add following dependency into your pom
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-jasper</artifactId>
<scope>provided</scope>
</dependency>
It should work. For more reference you can follow this tutorial
https://github.com/spring-projects/spring-boot/tree/v2.1.1.RELEASE/spring-boot-samples/spring-boot-sample-web-jsp

RabbitListener is not an annotation type

I have a basic Spring Boot web project and I am using Spring Tool Suite. I am trying to implement a basic messaging with RabbitMQ, but I am not able to import RabbitListener annotation. I get error message in IDE RabbitListener is not an annotation type.
pom.xml
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>jms.client</groupId>
<artifactId>msgClient</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>activemqSndClient</name>
<description>Spring-Boot activemq client </description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.4.2.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-jms</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.integration</groupId>
<artifactId>spring-integration-jms</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-amqp</artifactId>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.activemq/activemq-all -->
<dependency>
<groupId>org.apache.activemq</groupId>
<artifactId>activemq-all</artifactId>
<version>5.14.2</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
When I try to import RabbitListener class, I see error message The import org.springframework.amqp.rabbit.annotation.RabbitListener conflicts with a type defined in the same file, but I can see this class in maven dependencies.

Your class is named RabbitListener so it takes precendece to whatever you've imported. Rename it to something else and you'll be fine.