[jboss-user] [JBoss Seam] - Avoiding the DRY Principle with beans

[dhinojosa]

Question, I find myself doing something wrong with seam beans....and that is copying and pasting ad nauseum and violating the DRY Priniciple (Don't Repeat Yourself).   Here is a prime example


  | 
  | package com.evolutionnext.session;
  | 
  | import com.evolutionnext.data.Employee;
  | import java.io.Serializable;
  | import javax.ejb.Stateful;
  | import javax.persistence.EntityManager;
  | import javax.persistence.PersistenceContext;
  | import javax.persistence.PersistenceContextType;
  | import org.hibernate.validator.Valid;
  | import org.jboss.seam.ScopeType;
  | import org.jboss.seam.annotations.In;
  | import org.jboss.seam.annotations.Name;
  | import org.jboss.seam.annotations.Scope;
  | 
  | 
  | @Stateful
  | @Scope(value=ScopeType.SESSION)
  | @Name(value="employeeBean")
  | public class EmployeeBean implements Serializable, EmployeeLocal {
  |     
  |     @PersistenceContext(unitName="hrsystem",
  |     type=PersistenceContextType.EXTENDED)
  |     private EntityManager entityManager;
  |     
  |     @In @Valid
  |     private Employee employee;
  |     
  |     /** Creates a new instance of EmployeeBean */
  |     public EmployeeBean() {
  |     }
  |     
  |     public void setEmployee(Employee employee) {
  |         this.employee = employee;
  |     }
  |     
  |     @In @Valid
  |     public Employee getEmployee() {
  |         return employee;
  |     }
  |     
  |     public String update() {
  |         entityManager.merge(employee);
  |         return "Success";
  |     }
  |     
  |     public String create() {
  |         entityManager.persist(employee);
  |         return "Success";
  |     }
  |     
  |     public String delete() {
  |         entityManager.remove(employee);
  |         return "Success";
  |     }
  | }
  | 


All is well with this code...now what happens if I want the same functionality for uh...department, well I would need to copy and paste this code. This would violate the dry principal and make my app fragile in the process.

 One solution I thought would be to create a superclass and refactor my create, update, and delete methods.  This is almost an elegant solution but still has some copy/pasting problems.  Here is the code...




  | package com.evolutionnext.session;
  | 
  | import java.io.Serializable;
  | import javax.persistence.EntityManager;
  | import javax.persistence.PersistenceContext;
  | import javax.persistence.PersistenceContextType;
  | 
  | public abstract class PersistentBean  implements Serializable, PersistentLocal {
  |     
  |     @PersistenceContext(unitName="hrsystem",
  |     type=PersistenceContextType.EXTENDED)
  |     private EntityManager entityManager;
  |     
  |     private Object object;
  |     
  |     public abstract void setObject(Object object);
  |     
  |     public abstract Object getObject();
  |     
  |     public String update() {
  |         entityManager.merge(object);
  |         return "Success";
  |     }
  |     
  |     public String create() {
  |         entityManager.persist(object);
  |         return "Success";
  |     }
  |     
  |     public String delete() {
  |         entityManager.remove(object);
  |         return "Success";
  |     }
  | }
  | 

My EmployeeBean would like this now:


  | package com.evolutionnext.session;
  | 
  | import javax.ejb.Stateful;
  | import org.jboss.seam.ScopeType;
  | import org.jboss.seam.annotations.In;
  | import org.jboss.seam.annotations.Name;
  | import org.jboss.seam.annotations.Out;
  | import org.jboss.seam.annotations.Scope;
  | 
  | /**
  |  *
  |  * @author Administrator
  |  */
  | @Stateful
  | @Scope(value=ScopeType.SESSION)
  | @Name(value="employeeBean")
  | public class EmployeeBean extends PersistentBean {
  |     
  |     /** Creates a new instance of EmployeeBean */
  |     public EmployeeBean() {
  |     }
  |     
  |     private Object object;
  |     
  |     public void setObject(Object object) {
  |         this.object = object;
  |     }
  |     
  |     @In(value="employee") @Out(value="employee")
  |     public Object getObject() {
  |         return object;
  |     }
  |     
  | }
  | 
  | 

I am not even sure if this type of subclassing works in Seam.  Is this what I have to look to as far as abstraction.  Let me know. ;)

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