How to not repeat code within catch blocks?

Question

I am having a hard time not to repeat myself in a Java program I am working on at the moment.

Say, I need to declare a lot of methods that basically are structured in the following way:

public SomeEntity doSomething (String someAttribute, String anotherAttribute) {     EntityManager em = this.createEntityManager();      EntityTransaction tx = null;     try {          /*          * ... independent logic ...          */          tx = em.getTransaction();     } catch (RuntimeException e) {         if (tx != null && tx.isActive()) {              tx.rollback();         }         throw e;     } finally {         em.close();     }      return something; } 

The method body of all methods needs to contain theses elements for resource management.

The "independent logic" itself will be rather complex too, so putting the try/catch statement in a separate method won't really work.

I want to avoid to repeat this code. What are the best practices to apply in these situations?

Answer 1

Create an interface:

public interface EntityManagerAction {    public void execute(EntityManager em); } 

And a utility class:

public class EntityUtil {   public static void executeWithEntityManager(EntityManagerAction action) {     EntityManager em = someHowCreateEntityManager();      EntityTransaction tx = null;     try {         action.execute(em);         tx = em.getTransaction();     } catch (RuntimeException e) {         if (tx != null && tx.isActive()) {              tx.rollback();         }         throw e;     } finally {         em.close();     }   } } 

Now you can re-use the boiler-plate in the EntityUtil class, and your code becomes:

public SomeEntity doSomething (String someAttribute, String anotherAttribute) {    Something something;     EntityUtil.executeWithEntityManager(new EntityManagerAction() {         public void execute(EntityManager em ) {          /*          * ... independent logic ...          */          //use the passed in 'em' here.         }     });      return something; } 

See also What is the "Execute Around" idiom?