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Spring / GWT Software Architecture for scalable applications – Part 2

with 7 comments

During this article you will learn how to build efficiently and quickly the backend (based upon the solution described on part one : that is going to be used later by any kind of clients (GWT, Android,…). My aim is to guide step by step on building an example application and gives you all the best practices on each step to achieve high quality code.

Specifically, you will do the following in this article:

  • Methodology based on UI prototyping to define the service layer of the application (how many services, what functionality’s they must offer…)
  • Setting up the infrastructure of the project : libraries, configuration files, logger…
  • Setting up the persistence layer : business entities, persistence related configuration files…
  • Setting up the DAO layer using Spring Data API : bind queries to DAO methods, conventional DAO method naming.
  • Setting up the service layer : transaction configuration, security configuration.
  • Setting up Test classes using JUnit and Spring Test.

Extracting services

From my experience the best way to determine the required services is by establishing first all the UI prototype for your web application, the next step is to analyze all prototypes carefully and try to form groups of coherent and consistent features which are our services.

Below UI prototype of the application we are going to build during this prototype :

From this annotated UI prototype you can clearly see that we have tow services, one for managing Transactions and the other for Accounts. Each services contain the following methods :

  • Transaction service contain a reference to TransactionRepo and AccountRepoand have the following methods :
    • add(Transaction new) : for adding a new transaction, it should also update the account balance.
    • loadTransactionByAccountId(accountId, period, type) : load transactions of the selected account and selected period (this month, this quarter, this year…) and type filter (income, expense, all).
    • loadTotalAmountByAccountId(accountId, period, type) : calculate the total amount of transactions of the selected account and selected period and type filter.
  • Account service contain a reference to AccountRepo and TransactionRepo have the following methods :
    • loadAll() : load all accounts.
    • add(Account new) : for adding a new account, if the initial balance is specified should create a new Income transaction attached to this account.

Back end infrastructure

In order to speed up the project setup (libraries, log4j setting, applicationContext…) I choose to use Spring Roo which will prepare all required infrastructure code for a spring based project. On this project I’m going to use the following  libraries and tools :

  • MongoDB : I choose to use a NoSQL database instead of the old relational one (Just a personal preference). For more information about how to setup the latest version of MongoDB on Ubuntu  see
  • Spring ROO 1.2 the first version that support MongoDB code generation and service oriented architecture see for more information.
  • I’ll be using SpringSource Tool Suite 2.8.1 as IDE which is the best environment to build Spring powered applications, see

To prepare our project, in STS create a new ROO project, give it a name and the topLevelPackage, then ROO generate automatically all required files (Log4j, applicationsContext, pom.xml,…) for a Spring project, normally this project works out of the box.

Business entities setup

From the ROO shell we are going to setup mongo database and create our tow business entities (Account and Transaction) :

//Setting up mongo add-on
mongo setup

//Creating the Account entity
entity mongo --class ~.domain.Account
field string --fieldName name --notNull
field number --fieldName balance --type double

//Creating the Transaction entity
entity mongo --class ~.domain.Transaction
field string --fieldName payee
field other --fieldName accountId --type org.bson.types.ObjectId
field date --fieldName dateTransaction --type java.util.Date --notNull
field string --fieldName tags
field string --fieldName type --notNull
field number --fieldName amount --type double

You did notice that the Transaction entity hold the ObjectID of the Account (because there is a one to many relation between the tow entities), to simplify things I prefer to manage this association manually without using advanced concept like DBRef or embedded lists.

Repository layer setup

Beginning from Spring ROO 1.2, there is support for generating Spring Data repositories (service oriented architecture).

The generated DAO’s offer simple database access methods (create, update, findAll…), we can add our own custom methods by following naming convention no implementation code need (see for more details) or if we have complexes queries with some business logic we declare them in the Repository interface and write theirs implementation (see

From ROO shell I’m going to create tow empty DAO one to manage Account and the other for Transaction :

//Account Repository
repository mongo --interface ~.repository.AccountRepo --entity ~.domain.Account

//Transaction Repository
repository mongo --interface ~.repository.TransactionRepo --entity ~.domain.Transaction

Theses repositories contain only standard methods offered by MongoRepository abstract class (more detail we still need to add our custom methods for both AccountRepository and TransactionRepository manually.

Account repository

From the list of methods extracted (loadAll, add) in the Account service we see that they already exists on the MongoRepository, except that when adding a new transaction we need to update the current balance of the account attached to the transaction, this can’t be done with just a conventional naming DAO method.

//DAO methods without implementation code : conventional naming
@RooMongoRepository(domainType = Account.class)
public interface AccountRepo extends AccountRepoAdvance {
    List<Account> findAll();

    Account findByName(String name);

//Advanced DAO methods which required implementation code
public interface AccountRepoAdvance {
    void updateAccountBalance(BigInteger accountId, Double transactionAmount, String type);

public class AccountRepoImpl implements AccountRepoAdvance {
    MongoOperations mongoOps;

    public void updateAccountBalance(BigInteger accountId, Double transactionAmount, String type) {
        //Implementation code Here...

Transaction repository

On this repository we need a conventional method to load transactions by accountId, period and type (no need for code implementation), this method have to be called findByAccountIdAndDateBetweenAndTypeLike this name will be parsed by Spring Data in order to generate the query on the fly.

Spring Data conventional naming

The last required DAO method is totalAmountByAccountId, this one is an aggregation query and will use the group feature of MongoDB. This method can’t be implemented using the conventional naming way because we have to use the MongoOperations object to execute this kind of more advanced queries.

Below a snippet of code source for TransactionRepository :

//DAO methods without implementation code : conventional naming
@RooMongoRepository(domainType = Transaction.class)
public interface TransactionRepo extends TransactionAdvancedRepo {
    List<Transaction> findByAccountIdAndDateBetweenAndTypeLike(ObjectId accountId,
            Date start, Date end, String type);

//Advanced DAO methods which required implementation code
public interface TransactionAdvancedRepo {
    Double totalAmountByAccountId(ObjectId accountId, Date start,Date end, String type);

class TransactionAdvancedImpl implements TransactionAdvancedRepo {
    MongoOperations mongoOps;

    public Double totalAmountByAccountId(.....) {
        //Implementation code Here...

Check out this great cheat sheet if you are an experienced SQL programmer and want to learn how to write MongoDB queries.

Service layer setup

The final step on this tutorial is to setup the service layer, this layer use services offered by the repository (plain simple CRUD and querying methods)  and add to them the business logic. For example when adding a new transaction we are going to use the method save of the repository TransactionRepo but also we need to assure that the balance of the account attached to this transaction is updated (this is the business logic to control).

I’m going  also to use ROO to generate the service layer, by typing the following commands :

//Account Service
service --entity ~.domain.Account --interface ~.service.AccountService

//Transaction Service
service --entity ~.domain.Transaction --interface ~.service.TransactionService
ROO will generate nice and clean services holding a reference for the required repository (all this code is hidden in generated aspects, it is just an infrastructure code). Below the source code of the generated interfaces along with extracted methods described earlier :
@RooService(domainTypes = { Account.class })
public interface AccountService {
    void addNewAccount(Account account);
    List<Account> loadAllAccounts();

//The TransactionService require both Transaction and Account repositories
@RooService(domainTypes = { Transaction.class, Account.class })
public interface TransactionService {
    void addNewTransaction(Transaction transaction);
    List<Transaction> loadTransactionsByAccountId(BigInteger accountId, Integer period,
            String type);
    Double loadTotalAmountByAccountId(BigInteger accountId, Integer period, String type);
I’m not going to describe in here the implementation code of the service, at the end of this article there is an archive containing the whole project.

Testing Services and repositories

The last step on this article, is to test if everything works the way we want, this is a very crucial step on building a great and organized service layer, and generally on this step sometimes we intend to tweak a little bit the repositories, entities and services if we forgot something in step 1.

Because we are working on a little example, all what I’m going to show is how to test services and see if they works correctly using JUnit and Spring Test (for more details visit, for more details see the code below  :

public class TestServices {
    @Autowired AccountRepo accountRepository;
    @Autowired TransactionRepo transactionRepository;
    @Autowired AccountService accountService;
    @Autowired TransactionService transactionService;

    public void cleaningOldData() {

    public void testCreatingAccount() {
        //Test creating new Account here...

    //... More Test Methods here, check attached source code for more details

That’s it for this article, I hop that you have a big picture of the back end part, this is just a little example but I think it will help some of you to build easily high quality application very quickly. I’m open to any suggestion or enhancement.

Full Project source code can be downloaded from here : Project source.


Written by imrabti

January 2, 2012 at 11:35 am

Spring / GWT Software Architecture for scalable applications – Part 1

with 18 comments

During this article I’m willing to share with you a clean software architecture to build high scalable enterprise application based upon GWT (on the front end) and Spring (on the back end).

I’m going to start by showing the overall software architecture and describing all technologies and best practices I use, then on the next articles we will build a little application from scratch step by step, on each article we are going to concentrate on a precise part of the solution.

GWT/Spring Software architecture

The solution is composed from tow parts, the client side (GWT) and the server side (Spring/JEE).

Client side (GWT)

On GWT I use the MVP design pattern along with activities, and RequestFactory. On this solution the MVP is just an abstraction and it is implemented using activities, the presenter and RequestFactory.

On the table below I describe each letter of MVP and how is implemented in the solution :

MVP Model

On this architecture the objects creation and injection (this include views, remote interfaces, event bus…) is managed by an IoC framework (like Spring) called GIN and is based upon Google Guice. I’ll show you on the next article how to configure it and how I use it on this approach.

  • View is a singleton configured using GIN (GWT IoC framework), most of the time a view is used by just one activity.
  • Presenter is an interface implemented by a given view, to give a lightweight object which will be manipulated later by the activity to interact with the view.
  • Activity It contains no Widgets or UI code and have a lifecycle. All the code about the UI business logic is written here. Activities manipulate both the view (by the intermediate of the presenter) and models (by calling the RequestFactory) and are started and stopped by an ActivityManager that is associated with a container Widget (a certain display area on the screen).
  • Event Bus is a singleton configured using GIN and can be injected on activities and views, its function is to dispatch events to interested parties. An event bus eases decoupling by allowing objects to interact without having direct dependencies upon one another.
  • RequestFactory is a factory exposing all your RequestContext. Each spring service you want to expose to the client must have its clone interface on GWT which extends the interface RequestContext.
  • Proxy are the clones of the objects (business objects or VO’s) used on the spring services in the server side they are manipulated by the remotes interfaces (interfaces which extends RequestContext), activities and views on GWT.

Server side (Spring/JEE)

On the server side I use a simple service oriented architecture composed from DAO (data access object managed by Spring Data for JPA), services (transactional and secured service layer exposed to GWT through the RequestFactory API),  and finally persistent entities or value objects (theses are manipulated by services and DAO).

  • Spring Data JPA repositories : Interfaces that extends the Spring Data generic repository, this interface offer elementary DAO methods (save, update, find all…), we can also put here our simple DAO methods (only methods definitions no implementation required) see Spring Data documentation for more informations :
  • Custom repositories : Here we put advanced DAO methods that needs some business logic code not just simple queries like JPA repositories (the implementation of the custom interfaces is required).
  • NamedQueries XML File : Both Spring Data Repositories and Custom repositories loads queries from XML files instead of hard coding them in java classes.
  • Spring services : Here we have all the functionality that our server side expose to the client. In order to manipulate data a service is composed from one or many DAO’s, also all the methods of the service must be transactional (so we can rollback if there is an accident) and secure.

Project structure

Now that we know some foundations about the solution, I’m going to show you how is the project structured :

The project is divided in tow big packages, the server side and client side.

Structure of the server side

On the server side we have the following sub packages :

  • repos: composed from tow other packages ‘simple’ which contain spring data DAO’s interfaces and ‘advanced’ which contain advanced DAO’s (this type of DAO’s uses the EntityManager and they perform some business logic on data).
  • services: here we found the interfaces and implementation of services exposed to GWT client.
  • rest: here we put REST controller to expose a REST API to build for example native iOS or Android application.
  • business: here we have persistent entities and custom types (like enumerations or abstract classes).
  • security: all classes related with security like authentication service, security filters… (I use spring security to manage the security of the application).

Structure of the client side

On the client side we have the following sub packages :

  • activity: holds all activities, in each activity there is an inner interfaces which is the presenter implemented by the view.
  • place: here we find the places, a place is used by the ActivityManaged defined for each display region on the GWT shell (or layout) to decided which activity to load. I’m going to talk about places on the following articles.
  • UI: holds all the declarative XML files or java code to describe the UI (UI Binder). I also put in here the application layout (I called the shell). Every other files except layout related files are grouped on sub packages each one contain the UI’s that concern a certain module of the application.
  • event: contain all the custom event we use on the EventBus. The event on here are used for example to update the content of a view when we receive some data, when another display managed by another activity trigger an event. Check this article to learn more about how to use events on a MVP architecture.
  • request: here we find RequestContext interfaces in relation with Spring services on the back end, the communication is done using a RequestFactory servlet, for more information about how to integrate Spring and GWT check the following article The sub package proxy holds the value object exchanged between the client GWT and server Spring, they are a representation of the remote objects (entities or VO’s) managed by Spring on the client side.
  • ioc: holds infrastructure code to set up the IoC container on the client (configuration for GIN). The ‘MyAppModule’ file configure the beans managed by GIN container and theirs scope (Singleton, Provider…) this file is like the applicationContext.xml on Spring.  The ‘MyAppInjector’ indicate which of the defined beans we want to get to explicitly (anywhere even if it is not a GIN bean) it is like a factory of beans. A given application can have multiples ‘Modules’ and ‘Injectors’ files.
  • resource: here we host the custom style files and images, I use heavily the ClientBundle GWT API to learn more check

That’s it for this article, on the following article I’ll describe the example we are going to build step by step using this architecture.

Written by imrabti

December 6, 2011 at 9:52 am