In the last tutorial we saw how to use Java 8 methods in projection interface to apply custom query logic. Another more flexible option is to implement custom logic in a Spring bean and invoke the bean methods from the projections' SpEL expressions.
Quick Example
The bean:
@Component
public class EmployeeInfoBean {
public String getDisplayString(Employee employee) {
//apply custom logic here
}
}
The projection interface:
public interface EmployeeInfo {
@Value("#{@employeeInfoBean.getDisplayString(target)}")
String getDisplayString();
}
As seen above, the symbol @ is used to access the bean reference in SpEL expression.
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;
.............
}
The Bean
@Component
public class EmployeeInfoBean {
public String getDisplayString(Employee employee) {
return String.format("%s (%s)", employee.getName(), employee.getDepartment().getDeptName());
}
public String getDetailedString(Employee employee, String labelName, String labelDept) {
return String.format("%s: %s, %s: %s, %s",
labelName, employee.getName(),
labelDept, employee.getDepartment().getDeptName(),
employee.getDepartment().getLocation());
}
}
Projection interface
public interface EmployeeInfo {
@Value("#{@employeeInfoBean.getDisplayString(target)}")
String getDisplayString();
@Value("#{@employeeInfoBean.getDetailedString(target, args[0], args[1])}")
String getDetailedString(String labelName, String labelDept);
}
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()));
System.out.println("-- detailed display strings --");
list.forEach(employeeInfo -> {
String str = employeeInfo.getDetailedString("Employee", "Department");
System.out.println(str);
});
}
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 class
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 -- Diana (Admin) Mike (IT) Rose (Sales) Sara (Admin) Joe (IT) Charlie (IT) -- detailed display strings -- Employee: Diana, Department: Admin, NY Employee: Mike, Department: IT, TX Employee: Rose, Department: Sales, NC Employee: Sara, Department: Admin, TX Employee: Joe, Department: IT, TX Employee: Charlie, Department: IT, NY
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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