Spring-data : Error creating bean with name 'mainController': Unsatisfied dependency expressed through field 'userService'

I am new to spring-boot, when i try to run the mvn clean install the terminal gives me this ERROR:

[ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 7.465 s <<< FAILURE! - in com.example.accessingdatamysql.AccessingDataMySqlApplicationTests
[ERROR] contextLoads  Time elapsed: 0.001 s  <<< ERROR!
java.lang.IllegalStateException: Failed to load ApplicationContext
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'mainController': Unsatisfied dependency expressed through field 'userService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userServiceImpl': Unsatisfied dependency expressed through field 'mapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.accessingdatamysql.util.UserMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userServiceImpl': Unsatisfied dependency expressed through field 'mapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.accessingdatamysql.util.UserMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.accessingdatamysql.util.UserMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

[INFO]
[INFO] Results:
[INFO]
[ERROR] Errors:
[ERROR]   AccessingDataMySqlApplicationTests.contextLoads » IllegalState Failed to load ...
[INFO]
[ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  13.677 s
[INFO] Finished at: 2020-10-03T22:37:51+02:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.22.2:test (default-test) on project accessingdatamysql: There are test failures.

I tried them all a bit but I can't get it started correctly, I've been stuck in this state for several days
I add the various parts of the project
AccessingDataMysqlApplication.java

package com.example.accessingdatamysql;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.domain.EntityScan;
import org.springframework.context.annotation.ComponentScan;


@SpringBootApplication
public class AccessingDataMysqlApplication {

  public static void main(String[] args) {
    SpringApplication.run(AccessingDataMysqlApplication.class, args);
  }

}

MainController.java

package com.example.accessingdatamysql.rest;





import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.example.accessingdatamysql.model.dto.UserDto;
import com.example.accessingdatamysql.service.UserService;


@RestController
public class MainController {
	
@Autowired 
private UserService userService;

  @Transactional
  @PostMapping(path="/demo/add")
  public @ResponseBody String addNewUser (@RequestParam String name
      , @RequestParam String email,@RequestParam String surname) 
  {
 

    UserDto n = new UserDto();
    n.setName(name);
    n.setSurname(surname);
    n.setEmail(email);
    userService.create(n);
	return "Saved";
  }



 


  @GetMapping("/demo/first")
  public UserDto one(@RequestParam String name) {
   System.out.print(name);
  return userService.findFirstByName(name); 
  }
}

UserService.java

package com.example.accessingdatamysql.service;

import org.springframework.stereotype.Service;

import com.example.accessingdatamysql.model.dto.UserDto;

@Service
public interface UserService {

	UserDto findFirstByName(String name);
	
	void create(UserDto user);
    	
}
  

UserServiceImpl.java

package com.example.accessingdatamysql.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.example.accessingdatamysql.model.dto.UserDto;
import com.example.accessingdatamysql.model.entity.UserEntity;
import com.example.accessingdatamysql.model.repo.UserRepository;
import com.example.accessingdatamysql.util.UserMapper;

@Service
public class UserServiceImpl implements UserService{
	
	@Autowired
	  private UserRepository userRepository;
	
	@Autowired
    UserMapper mapper;

	@Override
	public UserDto findFirstByName(String name) {
		   UserEntity entity = userRepository.findFirstByName(name);
		   
		return mapper.toDtoMapper(entity);
	}

	@Override
	public void create(UserDto user) {
         UserEntity entity = mapper.toEntityMapper(user);
         
         userRepository.create(entity);
		
	}
 
}

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>2.3.4.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>accessingdatamysql</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>project</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
			</properties>

	<dependencies>
			<dependency>
			<groupId>org.mapstruct</groupId>
			<artifactId>mapstruct</artifactId>
			<version>1.3.1.Final</version>
		</dependency>
		<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>

The structure of my project is this:

src->com->example->accessingdatamysql|----->model
                                     |----->repo
                                     |----->util
                                     |----->service
                                     |----->rest----->Main.Controller.java
                                     |----->AccessingDataMysqlApplication.java

UserMapper.java

package com.example.accessingdatamysql.util;

import org.mapstruct.Mapper;

import com.example.accessingdatamysql.model.dto.UserDto;
import com.example.accessingdatamysql.model.entity.UserEntity;


@Mapper (componentModel = "spring")
public interface UserMapper {

    UserEntity toEntityMapper (UserDto user);
    
    UserDto toDtoMapper (UserEntity userEntity);
}

I tried to make changes With the MainController, to change the Controller but there are no changes. Entering either @EntityScan or @Component didn't help me in any way

The issue is that spring is not able to create a bean of this type: com.example.accessingdatamysql.util.UserMapper
It claims that there are no implementations of it.
Check your annotations on that class.

I found the problem in UserService. UserService uses UserMapper interface but UserMapper is not a Spring managed bean. So @Autowired annotation does not work with UserMapper. Remove @Autowired from UserMapper and use UserMapper following MapStruct guidelines and the problem should be solved.

Your code should look like this. In UserService.java

UserMapper userMapper = Mappers.getMapper( UserMapper.class );

I also found that you missed maven plugin for mapstruct. You need to add this plugin for mapstruct to work.
Your plugins section in pom.xml should look like this.

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.5.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
                <annotationProcessorPaths>
                    <path>
                        <groupId>org.mapstruct</groupId>
                        <artifactId>mapstruct-processor</artifactId>
                        <version>1.3.1.Final</version>
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>
    </plugins>
</build>

Hope this helps. For further information you can look at
https://mapstruct.org/
https://www.baeldung.com/mapstruct