As an alternative to projection interface having methods with SpEL, we can use Java 8 default methods for custom logic.
Quick Example
public interface EmployeeInfo {
String getName();
Department getDepartment();
default String getDisplayString() { //custom logic
return String.format("Name: %s, Dept: %s", getName(),
getDepartment().getDeptName());
}
}
Complete Example
Entities
@Entity
public class Employee {
@Id
@GeneratedValue
private Integer id;
private String name;
@ManyToOne(cascade = CascadeType.ALL)
private Department department;
private int salary;
.............
}
@Entity
public class Department {
@Id
@GeneratedValue
private Integer id;
private String deptName;
private String location;
.............
}
Projection interface using default method
public interface EmployeeInfo {
String getName();
Department getDepartment();
default String getDisplayString() {
return String.format("Name: %s, Dept: %s", getName(),
getDepartment().getDeptName());
}
}
Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
List<EmployeeInfo> findBy();
}
Example Client
@Component
public class ExampleClient {
@Autowired
private EmployeeRepository repo;
public void run() {
List<Employee> employees = createEmployees();
repo.saveAll(employees);
System.out.println("-- finding all employees --");
Iterable<Employee> all = repo.findAll();
all.forEach(System.out::println);
System.out.println("-- All EmployeeInfo --");
List<EmployeeInfo> list = repo.findBy();
System.out.println("-- display strings --");
list.forEach(employeeInfo -> System.out.println(employeeInfo.getDisplayString()));
}
private List<Employee> createEmployees() {
return Arrays.asList(
Employee.of("Diana", Department.of("Admin", "NY"), 3000),
Employee.of("Mike", Department.of("IT", "TX"), 35000),
Employee.of("Rose", Department.of("Sales", "NC"), 4000),
Employee.of("Sara", Department.of("Admin", "TX"), 3500),
Employee.of("Joe", Department.of("IT", "TX"), 3000),
Employee.of("Charlie", Department.of("IT", "NY"), 4500)
);
}
}
Main method
public class ExampleMain {
public static void main(String[] args) {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(AppConfig.class);
ExampleClient exampleClient = context.getBean(ExampleClient.class);
exampleClient.run();
EntityManagerFactory emf = context.getBean(EntityManagerFactory.class);
emf.close();
}
} -- finding all employees -- Employee{id=1, name='Diana', department=Department{id=2, deptName='Admin', location='NY'}} Employee{id=3, name='Mike', department=Department{id=4, deptName='IT', location='TX'}} Employee{id=5, name='Rose', department=Department{id=6, deptName='Sales', location='NC'}} Employee{id=7, name='Sara', department=Department{id=8, deptName='Admin', location='TX'}} Employee{id=9, name='Joe', department=Department{id=10, deptName='IT', location='TX'}} Employee{id=11, name='Charlie', department=Department{id=12, deptName='IT', location='NY'}} -- All EmployeeInfo -- -- display strings -- Name: Diana, Dept: Admin Name: Mike, Dept: IT Name: Rose, Dept: Sales Name: Sara, Dept: Admin Name: Joe, Dept: IT Name: Charlie, Dept: IT
Example ProjectDependencies and Technologies Used: - spring-data-jpa 2.0.9.RELEASE: Spring Data module for JPA repositories.
Uses org.springframework:spring-context version 5.0.8.RELEASE - hibernate-core 5.3.5.Final: Hibernate's core ORM functionality.
Implements javax.persistence:javax.persistence-api version 2.2 - h2 1.4.197: H2 Database Engine.
- JDK 1.8
- Maven 3.5.4
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