mapstruct generated implementation cannot find imported class in multi-module Spring Boot project

Question

I am using clean architecture and have 3 modules: application -> details -> core
I'm trying to use Mapstruct to generate mappers in application & mappers in details. I have this mapper in application module

When I do mvn package in the parent pom to build all modules then mvn spring-boot:run -pl application when I send a request & hit the mapper method it throws this error

java.lang.Error: Unresolved compilation problems: 
        The import com.aura.app.http.rest.v1.institutions.requests cannot be resolved
        The import com.aura.app.http.rest.v1.institutions.responses cannot be resolved
        AppInstitutionMapper cannot be resolved to a type
        CreateInstitutionRequestDTO cannot be resolved to a type
        InstitutionResponseDTO cannot be resolved to a type
        The method from(Institution) of type AppInstitutionMapperImpl must override or implement a supertype method
        InstitutionResponseDTO cannot be resolved to a type
        InstitutionResponseDTO cannot be resolved

        at com.aura.app.http.rest.v1.institutions.mappers.AppInstitutionMapperImpl.<init>(AppInstitutionMapperImpl.java:3) ~[classes/:na]
        at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62) ~[na:na]
        at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499) ~[na:na]
        at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:483) ~[na:na]
        at org.mapstruct.factory.Mappers.doGetMapper(Mappers.java:85) ~[mapstruct-1.6.3.jar:na]
        at org.mapstruct.factory.Mappers.getMapper(Mappers.java:69) ~[mapstruct-1.6.3.jar:na]
        at org.mapstruct.factory.Mappers.getMapper(Mappers.java:58) ~[mapstruct-1.6.3.jar:na]
        at com.aura.app.http.rest.v1.institutions.mappers.AppInstitutionMapper.<clinit>(AppInstitutionMapper.java:11) ~[classes/:na]
        at com.aura.app.http.rest.v1.institutions.InstitutionsController.createInstitution(InstitutionsController.java:51) ~[classes/:na]
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Method.java:565) ~[na:na]

AppInstitutionMapper.java:

package com.aura.app.http.rest.v1.institutions.mappers;

import com.aura.app.http.rest.v1.institutions.requests.CreateInstitutionRequestDTO;
import com.aura.app.http.rest.v1.institutions.responses.InstitutionResponseDTO;
import com.aura.core.institutions.entities.Institution;
import org.mapstruct.Mapper;
import org.mapstruct.factory.Mappers;

@Mapper
public interface AppInstitutionMapper {
    AppInstitutionMapper INSTANCE = Mappers.getMapper(AppInstitutionMapper.class);

    Institution from(CreateInstitutionRequestDTO dto);

    InstitutionResponseDTO from(Institution institution);
}

This is the generated AppInstitutionMapperImpl.java:

package com.aura.app.http.rest.v1.institutions.mappers;

import com.aura.app.http.rest.v1.institutions.requests.CreateInstitutionRequestDTO;
import com.aura.app.http.rest.v1.institutions.responses.InstitutionResponseDTO;
import com.aura.core.institutions.entities.Institution;
import javax.annotation.processing.Generated;

@Generated(
    value = "org.mapstruct.ap.MappingProcessor",
    date = "2025-11-07T00:04:30+0800",
    comments = "version: 1.6.3, compiler: javac, environment: Java 25 (Homebrew)"
)
public class AppInstitutionMapperImpl implements AppInstitutionMapper {

    @Override
    public Institution from(CreateInstitutionRequestDTO dto) {
        if ( dto == null ) {
            return null;
        }

        Institution.InstitutionBuilder institution = Institution.builder();

        institution.name( dto.getName() );
        institution.email( dto.getEmail() );
        institution.uen( dto.getUen() );
        institution.address( dto.getAddress() );
        institution.contactNumber( dto.getContactNumber() );

        return institution.build();
    }

    @Override
    public InstitutionResponseDTO from(Institution institution) {
        if ( institution == null ) {
            return null;
        }

        InstitutionResponseDTO.InstitutionResponseDTOBuilder institutionResponseDTO = InstitutionResponseDTO.builder();

        institutionResponseDTO.id( institution.id() );
        institutionResponseDTO.name( institution.name() );
        institutionResponseDTO.email( institution.email() );
        institutionResponseDTO.uen( institution.uen() );
        institutionResponseDTO.address( institution.address() );
        institutionResponseDTO.contactNumber( institution.contactNumber() );

        return institutionResponseDTO.build();
    }
}

The CreateInstitutionRequestDTO exists in the correct package, likewise for Institution .

In my parent pom I list out my modules like this:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
         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.aura</groupId>
    <artifactId>parent</artifactId>
    <version>1.0.0</version>
    <packaging>pom</packaging>
    <name>Aura Parent</name>
    <description>Parent POM for Aura</description>
    <modules>
        <module>core</module>
        <module>details</module>
        <module>application</module>
    </modules>
    <properties>
        <java.version>24</java.version>
        <maven.compiler.source>24</maven.compiler.source>
        <maven.compiler.target>24</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <!-- Dependency versions -->
        <spring.boot.version>3.5.6</spring.boot.version>
        <lombok.version>1.18.38</lombok.version>
        <mapstruct.version>1.6.3</mapstruct.version>
        <lombok-mapstruct-binding.version>0.2.0</lombok-mapstruct-binding.version>
        <keycloak-admin-client.version>26.0.7</keycloak-admin-client.version>
        <hibernate-envers.version>6.6.5.Final</hibernate-envers.version>
        <springdoc-openapi-stgarter-webmvc-ui.version>2.8.8</springdoc-openapi-stgarter-webmvc-ui.version>
        <spring-boot-starter-data-jpa.version>3.4.2</spring-boot-starter-data-jpa.version>
        <jakarta-validation-api.version>3.0.2</jakarta-validation-api.version>
        <archunit.version>1.4.1</archunit.version>
        <junit.version>4.13.2</junit.version>
        <slf4j.version>2.0.17</slf4j.version>
        <!--        used for liquibase profile, TODO: check if needed-->
        <liquibase.version>4.27.0</liquibase.version>
        <liquibase-maven-plugin.version>4.27.0</liquibase-maven-plugin.version>
        <liquibase-hibernate6.version>4.23.0</liquibase-hibernate6.version>
        <hibernate-validation.version>8.0.2.Final</hibernate-validation.version>
        <postgresql.version>42.7.5</postgresql.version>
    </properties>
    <dependencyManagement>
        <dependencies>
            <!-- Spring Boot BOM, only imports the SB dependency versioning -->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>${spring.boot.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

and in the application module, I import the dependencies from core & details module.

<?xml version="1.0"?>
<project 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"
         xmlns="http://maven.apache.org/POM/4.0.0">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.aura</groupId>
        <artifactId>parent</artifactId>
        <version>1.0.0</version>
    </parent>
    <packaging>jar</packaging>
    <artifactId>application</artifactId>
    <version>1.0.0</version>
    <description>aura application containing app runtime and configurations</description>
    <dependencies>
        <dependency>
            <groupId>com.aura</groupId>
            <artifactId>core</artifactId>
            <version>1.0.0</version>
        </dependency>
        <dependency>
            <groupId>com.aura</groupId>
            <artifactId>details</artifactId>
            <version>1.0.0</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>${slf4j.version}</version>
        </dependency>
        <!-- Liquibase -->
        <dependency>
            <groupId>org.liquibase</groupId>
            <artifactId>liquibase-core</artifactId>
            <version>${liquibase.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springdoc</groupId>
            <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
            <version>${springdoc-openapi-stgarter-webmvc-ui.version}</version>
        </dependency>
        <dependency>
            <groupId>org.keycloak</groupId>
            <artifactId>keycloak-admin-client</artifactId>
            <version>${keycloak-admin-client.version}</version>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct</artifactId>
            <version>${mapstruct.version}</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>${lombok.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-contract-shade</artifactId>
            <version>4.1.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <profiles>
        <profile>
            <id>generate-db-changelog</id>
            <build>
                <plugins>
                    <plugin>
                        <groupId>org.liquibase</groupId>
                        <artifactId>liquibase-maven-plugin</artifactId>
                        <version>${liquibase-maven-plugin.version}</version>
                        <configuration>
                            <propertyFile>src/main/resources/db/liquibase.properties</propertyFile>
                        </configuration>
                        <dependencies>
                            <dependency>
                                <groupId>org.liquibase.ext</groupId>
                                <artifactId>liquibase-hibernate6</artifactId>
                                <version>${liquibase-hibernate6.version}</version>
                            </dependency>
                            <!-- Add this dependency -->
                            <dependency>
                                <groupId>jakarta.validation</groupId>
                                <artifactId>jakarta.validation-api</artifactId>
                                <version>${jakarta-validation-api.version}</version>
                            </dependency>
                            <!-- Also add the implementation -->
                            <dependency>
                                <groupId>org.hibernate.validator</groupId>
                                <artifactId>hibernate-validator</artifactId>
                                <version>${hibernate-validation.version}</version>
                            </dependency>
                            <!-- Include your PostgreSQL driver -->
                            <dependency>
                                <groupId>org.postgresql</groupId>
                                <artifactId>postgresql</artifactId>
                                <version>${postgresql.version}</version>
                            </dependency>
                            <!-- Add your database driver dependency here -->

                        </dependencies>
                    </plugin>
                </plugins>
            </build>
        </profile>
    </profiles>
    <build>
        <finalName>report-api</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.11.0</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                    <release>${java.version}</release>
                    <!-- processes annotations -->
                    <annotationProcessorPaths>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>${mapstruct.version}</version>
                        </path>
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                            <version>${lombok.version}</version>
                        </path>
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok-mapstruct-binding</artifactId>
                            <version>${lombok-mapstruct-binding.version}</version>
                        </path>
                    </annotationProcessorPaths>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${spring.boot.version}</version>
                <configuration>
                    <mainClass>com.aura.app.Application</mainClass>
                    <layout>JAR</layout>
                    <excludes>
                        <!-- Exclude Lombok as it's not needed at runtime -->
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                    <!-- Force unpacking of module dependencies -->
                    <requiresUnpack>
                        <dependency>
                            <groupId>com.aura</groupId>
                            <artifactId>core</artifactId>
                        </dependency>
                        <dependency>
                            <groupId>com.aura</groupId>
                            <artifactId>details</artifactId>
                        </dependency>
                    </requiresUnpack>
                    <!-- This ensures classes are included in the JAR properly -->
                    <classifier>exec</classifier>
                </configuration>
                <executions>
                    <execution>
                        <id>repackage</id>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Since the annotations for mapper are successfully being processed in both details & application module, I do not know why when the application jar is run at runtime, the generated mapper implementation cannot find any of the other classes.

more details when i look into the jar of application module to check if the relevant classes are there i find that the classes are all there

the details module dependency is in classpath as a jar

jar tf application/target/report-api.jar | grep /details
> BOOT-INF/lib/details-1.0.0.jar

the mapper modules seem to be there too

jar tf application/target/report-api.jar | grep /mapper 
> BOOT-INF/classes/com/aura/app/http/rest/v1/institutions/mappers/
BOOT-INF/classes/com/aura/app/http/rest/v1/institutions/mappers/AppInstitutionMapper.class
BOOT-INF/classes/com/aura/app/http/rest/v1/institutions/mappers/AppInstitutionMapperImpl.class
BOOT-INF/classes/com/aura/app/http/rest/v1/institutions/mappers/UserMapper.class

the DTO class which the AppInstitutionMapperImpl could not find is also there

jar tf application/target/report-api.jar | grep /response
BOOT-INF/classes/com/aura/app/http/rest/v1/institutions/responses/
BOOT-INF/classes/com/aura/app/http/rest/v1/institutions/responses/InstitutionResponseDTO$InstitutionResponseDTOBuilder.class
BOOT-INF/classes/com/aura/app/http/rest/v1/institutions/responses/InstitutionResponseDTO.class

this is weird because the mapper class could not import the DTO class at runtime, however the DTO class is just literally in the same jar

Just a note: Since you're using Spring Boot, we recommend using the related dpedency injection. mapstruct.org/documentation/stable/reference/html/… It probably won't fix your issue, but it's good practice and certainly preferable. — Ray
– Ray, Commented Nov 6 at 21:51
@Ray Thanks for the suggestion. i tried it just in case and yea you're right, it did not work — kevin liu kai
– kevin liu kai, Commented Nov 7 at 7:13

Max · Accepted Answer · 2025-11-06 18:03:52Z

1

Have you tried to swap mapstruct-processor and lombok? Like this

<path>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>${lombok.version}</version>
</path>
<path>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct-processor</artifactId>
    <version>${mapstruct.version}</version>
</path>

Order might be important

answered Nov 6 at 18:03

Max

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4 Comments

kevin liu kai Nov 7 at 4:37

hey @max, i've tried it already and it did not work.

Max Nov 7 at 7:55

I understood. Need to add <dependency> <groupId>org.mapstruct</groupId> <artifactId>mapstruct-processor</artifactId> <version>${mapstruct.version}</version> </dependency> to dependency

kevin liu kai Nov 7 at 9:35

it worked! didnt know i need to import teh annotation processs in the actual runtime dependency. however im getting a similar issue in my applications module im using a class in the details module called InstitutionRepositoryImplm this class uses a InstitutionMapper also in details module. now this mapper throws the same error ``` java.lang.Error: Unresolved compilation problems: The import com.aura.details.tables cannot be resolved InstitutionMapper cannot be resolved to a type InstitutionTable cannot be resolved to a type ``` I added mapstruct-processor to det

kevin liu kai Nov 7 at 10:23

i solved the subsequent problem by building a standalone fat jar with with spring-boot-maven-plugin:repackage goal. I'm suspecting that the mapper in the details module could not import from core module somehow when not packaged as a fat jar.

kevin liu kai · Accepted Answer · 2025-11-13 13:16:32Z

0

Thanks @Max for solving this. I had to use spring-boot-mvn-plugin repackage goal to repackage the multiple modules to a standalone fat jar. this allowed the mapper classes to be able to import classes from other modules without errors

edited Nov 13 at 13:16

answered Nov 7 at 10:26

kevin liu kai

113 bronze badges

2 Comments

Ray Nov 8 at 8:10

If this is the solution, it indicates something is "off" with your project setup. The processor shouldn't be a runtime dependency. It doesn't add anything beyond the build time.

kevin liu kai Nov 13 at 13:16

you were right. i removed the processor from the runtime dependencies and it still works. It was just the repackaging build step that i needed

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