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Spring Data JPA - Invoking Bean Methods from Projections' SpEL expressions

[Updated: Aug 29, 2018, Created: Aug 29, 2018]

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 Project

Dependencies 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

Projections SpEL expression Invoking Bean Methods Select All Download
  • spring-data-jpa-projection-expression-calling-beans
    • src
      • main
        • java
          • com
            • logicbig
              • example
                • EmployeeInfo.java
          • resources
            • META-INF

    See Also