A module can not access JpaRepository interface that is in the other module - spring-data-jpa

Question

I am using IntelliJ and Gradle for a sample project. There are two modules.
demo-core module
It has entity and repository classes. build.gradle file is like the below.
apply plugin: 'java'
group 'com.example'
version '0.0.1-SNAPSHOT'
repositories {
mavenCentral()
}
dependencies {
implementation 'com.h2database:h2:1.4.200'
implementation 'org.springframework.boot:spring-boot-starter-data-jpa:2.5.3'
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.0'
}
test {
useJUnitPlatform()
}
I added CustomerRepository class for Customer entity in demo-core module.
package example.springboot.entity;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
#Repository
public interface CustomerRepository extends JpaRepository<Customer, Long> {
}
demo-web module
This is a web module and uses the repository interface like the below.
#SpringBootApplication
public class DemoWebApp {
public static void main(String[] args) {
SpringApplication.run(DemoWebApp.class, args);
}
#Bean
public CommandLineRunner demo(CustomerRepository repository) {
return (args) -> {
// save a few customers
repository.save(new Customer("Jack", "Bauer"));
repository.save(new Customer("Chloe", "O'Brian"));
repository.save(new Customer("Kim", "Bauer"));
repository.save(new Customer("David", "Palmer"));
repository.save(new Customer("Michelle", "Dessler"));
};
}
}
This is build.gradle file for demo-web module.
plugins {
id 'org.springframework.boot' version '2.5.3'
id 'io.spring.dependency-management' version '1.0.11.RELEASE'
id 'java'
}
group 'com.example'
version '0.0.1-SNAPSHOT'
repositories {
mavenCentral()
}
dependencies {
implementation project(':demo-core')
implementation 'org.springframework.boot:spring-boot-starter-web'
testImplementation 'org.springframework.boot:spring-boot-starter-test'
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.0'
}
test {
useJUnitPlatform()
}
but I can't use JpaRepsitory methods with this error.
/Users/dgkim/Downloads/demo/demo-web/src/main/java/example/springboot/DemoWebApp.java:19: error: cannot access JpaRepository
repository.save(new Customer("Jack", "Bauer"));
^
class file for org.springframework.data.jpa.repository.JpaRepository not found
So, I created a new interface wrapping the CustomerRepository in demo-core module like this.
#Service
public class CustomerFinder {
#Autowired
private CustomerRepository customerRepository;
public Optional<Customer> findCustomer(Long id) {
return customerRepository.findById(id);
}
}
My Controller class uses the wrapper interface like the below.
#RestController
public class CustomerController {
#Autowired
private CustomerFinder finder;
#GetMapping("/customer/{id}")
public String customer(#PathVariable Long id) {
Optional<Customer> customerOptional = finder.findCustomer(id);
if(customerOptional.isPresent()) return "find customer. " + customerOptional.get().getLastName();
else return "no entity";
}
}
It works. JpaRepository methods can be accessed in the same module but demo-web module that has a dependency on demo-core can not access it. DemoWebApp class can access CustomerRepository interface itself but can not access the super interface (JpaRepository).
How can I resolve this issue?

Answer 1

try to change core module dependencies from implementation to api
implementation 'org.springframework.boot:spring-boot-starter-data-jpa:2.5.3'
to
api 'org.springframework.boot:spring-boot-starter-data-jpa:2.5.3'
You can see the difference between api and implementation here