I am getting java.lang.ClassNotFoundException: Cannot find implementation for com.example.demo.mapper.DoctorMapper

Question

This is a mapper interface for mapping:

@Mapper
public interface DoctorMapper {
  DoctorMapper INSTANCE = Mappers.getMapper(DoctorMapper.class);
  DoctorDto toDto(Doctor doctor);
}

This is a model class:

public class Doctor {
  private int id;
  private String name;
  // getter and setter and constructors
}

This is a model class:

public class DoctorDto {
 private int id;
 private String name;
 // getter and setter and constructors
}

Controller class:

@RestController
public class SimpleController {
  @RequestMapping("/")
  String hello() {
    Doctor d= new Doctor(1,"Hari");
    DoctorDto doctorDto = DoctorMapper.INSTANCE.toDto(d);
    System.out.println(doctorDto.toString());
    return "Hello World, Spring Boot!";
  }
}

Any suggestion to map the doctor entity to doctordto? When I run the springboot application why do I encounter this issue?

java.lang.ClassNotFoundException: Cannot find implementation for com.example.demo.mapper.DoctorMapper
    at org.mapstruct.factory.Mappers.getMapper(Mappers.java:75) ~[mapstruct-1.4.2.Final.jar:na]
    at org.mapstruct.factory.Mappers.getMapper(Mappers.java:58) ~[mapstruct-1.4.2.Final.jar:na]
    at com.example.demo.mapper.DoctorMapper.<clinit>(DoctorMapper.java:11) ~[classes/:na]
    at com.example.demo.Controller.SimpleController.hello(SimpleController.java:18) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.18.jar:5.3.18]
    at 

Answer 1

You should not use "Mappers.get" in a spring boot context. Annotate your mapper with

componentModel = "spring",

and inject it like a normal bean.

private final DoctorMapper doctorMapper;

or

@Autowired
private DoctorMapper  

Also make sure that you have not just the dependency for mapstruct in your project but also the dependency for the generation of the mapperImpls

    <dependency>
        <groupId>org.mapstruct</groupId>
        <artifactId>mapstruct-processor</artifactId>
        <version>${org.mapstruct.version}</version>
        <scope>provided</scope>
        <optional>true</optional>
    </dependency>