Edit: There is no "right" or "wrong" answer here, I was merely trying to get people to share their dos and don'ts.
Behind this rather vague topic I would like to address a few problems I've been having in my last projects. As a general rule, I try to keep it simple, follow design patterns and the Single responsibility principle.But all those things leave certain questions unanswered, or at least unclear.
Let's consider this simplified example of a typical MVC WebApp from the Gui to the persistence layer (only snippets and pseudo code):
View.xhtml
<h:form>
<p:inputText value="#{model.text}" />
p:commandButton value="Save" actionListener="#{controller.saveToDb}" />
</h:form>
Model.java
String text;
String getText();
void setText(String text);
Controller.java
@Inject Model
@Inject Service
public void saveToDb(){
service.saveToDb(Model.getText());
}
Service.java
@Inject dao
public void saveToDb(String text){
Entity entity = new Entity(text);
dao.persist(entity);
This is just an illutration, but imagine several methods on every level, controllers calling services and services calling each other. (Some old schoolers may want to add a Facade between the controller and the service).
With this design in mind, here are a few questions:
What should methods return ? Void and Exceptions in case of errors ? Custom Result POJOs with values ?
How to implement error handling ? Checked or unchecked exceptions ? Do you handle a Service exception locally (if yes, what do you return ?), or do you throw it up to the caller ?
Is it OK for controllers to call other controllers ?
Do we really need a Value Object and Data Transfer Objects for every use case ? Why not send back entities ?
Should the Service check parameters, or should it just process data, assuming it has been checked before and it is correct ?
When checking data, is it OK to have several sequential checks, and return as soon as one fails ? (Bonus question: is is frowned upon to return in a void ?)
About single responsability: Imagine a scenario where you want to create a pojo, send it per http post and persist it. You would have:
- A service to create the pojo
- A service to send it via http post
- A service to persist it
- A controller reacting to a button clicked on the view
How and where do you combine the two ? Does the controller call the creation service method, then if successful the sending service method, and finally the persisting service method ?
Or is there one method in the controller called "createSendAndPersist()" that calls all 3 service methods in turn ? How do you handle errors in this case ?
I know, there are many ways to do this and there is no "right" answer. But what are best practices ? What did work best for you ?
