There are several Java source class files in our codebase (written in past) that has "service" in their name. All the methods in these service classes are static and some are like utility methods.
My question is - What kind of primary responsibility a service class should have? Is there a set of rules on should keep into consideration while designing a service?
As far as i know, service layer is responsible for keep business logic and talking to DAO layer. Its vary abstract and if you try to divide you app into just controller, service and dao, you will end up putting in lot of code under service layer.
I prefer to define service class as an entry point to my biz logic. That is controller can call only and only service layer. We try to avoid adding static methods to service layer.
Say I have a user service, it will expose methods related to users. Behind service layer we have dao, utilities dto entities etc. Also service class or anything below it can call other service classes.
Related
I wanted to know if ServiceFacade Design Pattern is really required while consuming a web-service.
http://soapatterns.org/design_patterns/service_facade
Any insight and code snippet would be really helpful.
Thanks in advance !!
The aim of the facade is to provide a forward (or client) facing endpoint, which in turn provides only what is needed for communication and hide anything which is behind it to the outside world.
Having a facade will allow you to abstract your behaviour without exposing it. It will also allow you to make changes without potentially affecting the endpoint itself. That depends on the type of changes obviously, but if you have some requirements which require some change in the logic it might be possible that the actual input and output of the service remain untouched.
If you where to do away with the service facade, any changes to the code might require your clients to update the code from their end, and those who, for some reason do not update might end up with a broken system or else you would have to cater for multiple versions.
Service Facade design pattern is not mandatory consuming a web-service. it is required when you don't want to expose core service contract changes.
How it works
You will define a core business service contract (CoreServiceContract)
You will define implementation for that contract (CoreServiceContractImpl)
You will define one service facade which is customer facing ( ServiceFacade )
This ServiceFacade holds the reference of contract - CoreServiceContract
You will invoke methods defined in CoreServiceContract through ServiceFacade. CoreServiceContract holds implementation of CoreServiceContractImpl
Advantages:
1) The Service Facade insulates the service definition from its implementation.
2) It is the way of decoupling the Web tier from the Business tier.
3) From a transactional point of view, the business service may implement his transaction scope or be part of the current transaction.
4) The contract of the Service Facade interface is oriented to be invoked by Web tier or client software, but methods of the contract should not be invoked
within the business implementation.
Have a look at this article for working code
currently I'm learning the SpringMVC + Hibernate. And I'm confused while implementing a simple user account manager application.
In my case:
the user account should be read from the database;
the password should be compared before any modification;
the user account information should be modified according to the frontend form;
the user account with new information should be save back to the database;
My questions are:
Should this whole process be implemented in the Service or in the Controller? And why?
In many examples I read that the service methods are usually tiny and contains only one DAO call, is this a good practice? Or we do the contrast to put several DAO calls into one service methods?
Should this whole process be implemented in the Service or in the Controller? And why?
Business logic is done in the service layer (the M in MVC) - see the link below for explanations.
In many examples I read that the service methods are usually tiny and contains only one DAO call, is this a good practice? Or we do the contrast to put several DAO calls into one service methods?
Service methods are of the proper size for the logic they perform. If for a particular logic you need access to several DAOs, or other services for that fact, you do so. If the logic is 10 lines of code or 100 then that's the size of the method. The thing is that most examples out there use a service layer (which your application should have) but because they are just that, examples, there isn't any logic in them. For this reason most of them just delegate to some DAO, confusing people about what their purpose should be.
Read the following for details: The Purpose of a Service Layer and ASP.NET MVC 2 (it's for .NET but the principles still apply).
What is the difference between Business Delegate and Service Locator.Do both responsible for encapsulating lookup and creation mechanism.If Business Delegate uses Service Locator for hiding lookup and creation mechanism then what is Business Delegate exclusively meant for, can't Service Locator replace Business Delegate.
I don't know if you already checked this out, but it's a good start.
Use a Business Delegate to encapsulate access to a business service. The Business Delegate hides the implementation details of the business service, such as lookup and access mechanisms.
A Service Locator encapsulates the logic required to search and/or obtain the location, restrictions and required fields for a certain service based on a general registry. A Business Delegate encapsulates a group of related services and exposes them in a cohesive way to prevent a service customer from having to search and access all the services related to a certain functionality.
Plus, you prevent the customer from having to actually know the Service Locator and the services it should consume, leaving that to a particular Business Delegate. A client only needs that delegate to perform a group of related tasks or a task that relies in various services.
Example
A Business Delegate doesn't actually encapsulate a group of Service Locators. It provides an abstraction layer over a Service Locator to provide a cohesive subset of services. Usually there's only one instance of a Service Locator, multiple instances require an additional mapping where you should know WHICH Service Locator provides Service X, think of it as if you would need a Service Locator Locator.
An example should help clarify things.
Think about user account management. The UserBusinessDelegate looksup the registration service to register an user and then looksup the authentication service to allow a log in. The client only needs one Business Delegate to access those services and he doesn't need to know the id of both services.
Those service ids are encapsulated in the UserBusinessDelegate avoiding the need of declaring the ids and using a Service Locator everywhere. Think about this, what would happen if one service id changes?.
In such cases the Business Delegate in charge is updated, avoiding a direct impact for the client.
These patterns have a common point therefore this question have a lot of sense.
Both of them help a client to consume a service.
Let suppose that we have services exposed as EJB, WS or POJO.
The client may access such services using the Service Locator directly. (allowing some complexity to be encapsulated inside this component)
This improve the cliente's side code but the client is still responsible for knowing how the service is exposed. (He has to select the right Service Locator for the specific service).
One disadvantage of this solution is that the client would be highly coupled with the service.
For example:
a) if tomorrow the service that is exposed as an EJB changes to WS we have to change the client's code (use another Service Locator).
b) If we want to test the client's code using a mock service, we have to change code.
Business Delegate come to scene to decrease the level of coupling.
Now the client interacts (in a higher abstraction level) with the Business Delegate, therefore he doesn't need to know anything else about service implementation details.
Of course the Service Locator is still useful due to the Business Delegate interacts with him.
At the simplest way, I like to think aboutn Business Delegate as an interface (improves decoupling) and a Service Locator as a helper (encapsulates infrastructure related behavior)
Ideally, controllers in a Spring MVC application must receive a request, despatch the request to an API, load the results (of the invocation) on to the model (for the view to subsequently render it) and forward to a view. They should do no more.
My controllers do far more than this today and I would like to move certain resposibilities away from the controller on to other APIs. My application design today (pretty typical):
controller <-> Service API <-> DAO <-> DB
The controller today fills up the delta between what the web app needs and what the Service API delivers.
I would like to place extra layer/layers between the controller and service API that chew away at this delta. My question is what layer(s) should these be and what should the responsibilities of these new layer(s)?
My current Idea is as follows
controller <-> controller helper <-> Business API <-> Service API <-> DAO <-> DB
Controller helper (web context aware - will depend on Model, HttpServlet and other web context classes):
Convert entities to DTO objects (2 way)
Resolve IDs to entities. E.g. Controller looks up a student i.d. (using a key) and converts it to a Student entity.
Business API (no web context dependency - can be JUnit tested):
Acts as a Facade. Invoking multiple service APIs to achieve one
business request.
Providing APIs that are specifically tailered for the web app.
Would you solve this a different way? Are there any resources (books, articles etc...) relating to this specific issue?
Some of previous discussions that did not answer my question:
Designing mvc controller layer
Service layer = Application layer = GRASP Controller layer
Moving Validation, Html Helpers to Service Layer in MVC
Thanks,
Vijay
Services contain the general business logic of an application. They are pretty much anything between Controllers and DAO/DB.
Your "business layer" and "controller helper" are just more services. I would keep the classic design for the sake of simplicity :
Controllers <-> possible Services <-> possible DAOs <-> DB
If I had lots of services (I usually don't) that happened to perform the same kind of logic, I would naturally split them into sub-packages. For example :
services.facade, or services.business
services.adapter for DTOs (except if you use simple classes to do this job)
A facade service is called by controllers like so : someFacade.someMethod(SomeDTO someDto). Then the facade handles DTO <-> Entity conversion thanks to other services (or simple classes).
That's how I would do in your context. In an ideal world (no legacy systems, or in a project from scratch), I'd directly use entities as form objects (instead of DTOs), and most of my services would be facades (the rest would be simple classes, if possible).
I'm new to Spring MVC and am also faced with this dilemma. Although Spring is new to me, I've been working with MVC for several years. I agree a controller should do no more than accept requests, dispatch them, and render the results in the correct format. I'm of the opinion that a service isn't necessarily the best place for the helper abstraction to exist though. I believe a service should encapsulate a specific API and do nothing more. I feel creating many 'types' of services convolutes this pattern and makes it unclear where the responsibilities fall.
It's my belief that helpers are better suited as siblings to services; they should be decorated with #Component instead of #Service. Their role is to act as a facade for the underlying APIs that are needed to transition state on the models exposed through the endpoint. The Controller->Helper->[Services] pattern promotes a clear separation of concerns, code-reusability, and is highly testable. The nature of this pattern is to prevent controller bloat, so you end up with ultra-thin controllers that really do nothing more than dispatch requests and render responses.
I've been working a lot with PHP.
But recently I was assigned some work which uses Java. In PHP I used to do a lot of Singleton object but this pattern has not the same signification in Java that it has in PHP.
So I wanted to go for an utility class (a class with static method) but my chief doesn't like this kind of classes and ask me to go for services object.
So my guess was that a service object is just a class with a constructor that implement some public methods...
Am I right?
Domain-Driven Design defines a Service as:
A SERVICE is an operation offered as an interface that stands alone in the model, without encapsulating state... [p. 105]
Yes, it's a class with public methods, but in addition to that, it implements an interface that exposes those methods. At its core, the Service is the interface - the class that implements it is just an implementation detail.
I found another definition for a service object instead that one described as an interface for concrete classes that are about to provide a certain service through that API definition set by the interface.
Article about Microservices >Link definition for service object:
3: Many object-oriented designers, including ourselves, use the term service object in the Domain-Driven Design sense for an object that carries out a significant process that isn't tied to an entity. This is a different concept to how we're using "service" in this article. Sadly the term service has both meanings and we have to live with the polyseme.
What I understand here its not the technical aspect like defining it as an "interface" but more the design concept it describes. I also understand an service object simply a domain of a class like its responsibility. So if you are developing web apps you might have a service object SecurityService which is a component of a SecurityController. The controller is calling the service to actually process security (the domain) specific services.