DDD Framework for Java: JdonFramework

Jdon Framework
(english)
github.com/banq/jdonframework
@jdonframework

What is Jdon?
 Jdon help you build a Clean and Fluent
architecture system.
 Jdon is a domain framework that let your business
to be independent with Database or UI.
 Jdon is a domain container to run your business in
non-blocking way.

Java Architecture
MVC
RESTful
struts1.x
Struts2
JSF
Tapestry
Wicket
Database
Hibernate
SQL
IBatis
NoSQL
micoservices
JdonFramework
Domain model

Jdon Framework (JF)
 a light-weight framework for developing Domain-
Driven Design applications.
 Jdon introduces reactive event-driven into domain.
 Help you develop a asynchronous concurrency
and higher throughput application

Jdon vs Spring
 Jdon is very difference with Spring
framework.
 Jdon is a default event-driven and
asynchronous framework.
 Jdon/Event- asynchronous vs.
Spring/Request-Response

Jdon’s Revolution
 Single Writer component model :DDD’s
AggregateRoot guards mutable state. And
Jdon guarantees single operation on in-
memory state by using Disruptor.
 Increases domain mode the level of
abstraction. Communication betwwen
Business Domain and others(UI/DB) is
Event/Message.

Jdon’s Revolution
 Two persistence choices between State and
Event: SOA CQRS or EventSourcing.
 Make your applications high throughput and
lower latency.
 Scalable.

In-memory Programming Paradigm
 Jdon changes traditional programming
paradigm (Spring + Hibernate/JPA etc.)
 Make ORM be dead ,domain model is not
bind to any ORM framework.
 Make Data collection or Anemia model be
dead.

Lock vs Singel writer
 There are plenty of idioms to synchronize
multi-threaded access to a resource
 lock is sloooow, especially with a high
number of writer threads.
 In-memory Singel writer is Actors model
(Akka/Erlang etc.)

Blocking
 public class AggregateRoot{
 private ChannelState state;

 //tradional lock
 public void synchronized changeChannel(changeCommand cmd){
 state = cmd.getState();
 }
 }

Jdon NonBlocking
 public class AggregateRoot{
 private ChannelState state;

//single write
 @OnCommand("UserSaveCommand")
 public void changeChannel(changeCommand cmd){
 state = cmd.getState();
 }
 }

Jdon basic component Annotations
@Model : Aggregate Root Entity Model
@Service : Micro service or DDD service
@Component: Normal components.

AOP component Annotations
@Interceptor: AOP’s Interceptor
@Introduce: Advisor

1. Create a domain model
 A domain model is the aggregate root enity in DDD.
 DDD can help us find some domain models in business
requirement
 Example:
 public class MyModel {
 private String Id;
 private String name;
 ....
 }

Using @Model
 make sure the domain object in-memory cache:
 @Model
public class MyModel {
private String userId;
private String name;
....
}
 @Model is a jdon’s annotation for domain model.

Loading Model from Repository
@Introduce(“modelCache”) must be annotated in repository class
@Around must be annotated on the loading method.
GitHub Source code

2. Create a domain event
 Domain event is emitted from a domain
model, generally is a aggregate root entity,
 Jdon can help you develope domain event
easily.
 Jdon provides asynchronous
communication component model.
 Producer-Consumer or Publisher-
Subscriber pattern.

Four kinds of Producer-Consumer
 1. @Component -----> @model
 2. @model ------->@Component
 3. @Compponent ------> @Component
 4. @model------> @model

Producer-Consumer
Procuder:
@Introduce("message") is for Producer class;
@send is for Producer class’s method
Consumer:
@Consumer is for Consumer class
@OnEvent is for Consumer class’s method.

Single Writer Principle
Domain Model
Aggregate root
@Model
Disruptor
Queue
Command Single thread
Producer
@Component
@Service

Communications principle
 Powered by disruptor from LMAX
 Can handle 6 million orders per second on a
single thread
 recommended by Martin Fowler.

What is Domain Events
 Events that happened in the domain.
 captures the essence of business domains while staying
decoupled from platform complexity or hard performance
issues.
 No Block concurrent, No Lock ,so fast. fit for multi-core.
 Storage Ignorance ,Flexibility, Messaging Capabilities,
Scalable.

One Command =>Many Events
Domain Model
@Model
Other Components
@Componet
Logging
@Consumer
GUI
MVC
Client
Persistence
@Consumer
async
Message
async
Message
async
Message
Component architecture
Command

One Command=>one Domain Event
Domain Model
Aggregate root
@Model
Command
Producer
@Component
Consumer
@Consumer
@Component
Domain Events
Domain Model
Aggregate root
@Model
Command

Domain Events is basic for CQRS
User interface
Service
Domain
Event/Message BUSInfrastructure
Query/
Reporting
Commands
Commands
Events

How Domain Events work?
Domain Model
Aggregate root
@Model
Consumer
@Consumer
@Component
Disruptor
Or
Java
concurrent
Future
Domain Events

Event principle
Queue
Mychannel
Powered by Ringbuffer
@Send("mychannel") will push the DomainMessage into the
Queue, And the consumer will fetch it from the Queue.

Producer
 @Model or @Service/@Component can be
a Producer.
 When a Component/Service sends
messages to a Domain Model(aggregate
root), that is a command,
 When a domain model sends message to a
Component, that is a event

Consumer
 @Model cann’t be a Consumer
 Only @Component can be a Consumer.
 Two kinds of consumers:
 @Consumer is for a class.
 @OnEvent is for method of any @Component
 If there are several consumers, action’s order is by
the alphabetical of class name:AEventHandler =>
BEventHandler => CEvent…

Consumer return a result
 If you want to return a result in consumer,
you can set the result object into the
DomainMessage of the event in
DomainEventHandler :
 void onEvent(EventDisruptor event, boolean endOfBatch) throws Exception
{
 //return the result “eventMessage=hello”
 event.getDomainMessage().setEventResult("eventMessage=" +
myModel.getId());
 }

How to get the result?
 If a consumer return a result, that is a
asynchronous.
 event.getDomainMessage(). getEventResult()
 First times, maybe you can’t fetch it.
 Second times You can get it.
 You can call block method to fetch it a blocking
way, this is :
 event.getDomainMessage(). getBlockEventResult()

The benefits of @Consumer
 Atomic;
separates a transaction into single event
process, that is event stream.
 Asynchronous
saving datas to DB or Lucene is high
load, we can implement them with two
EventHandlers by different latency.

Domain Events(DE) apply in JEE
Root Entity
VO
Entity
Service
Root Entity
boundary
boundary
Tech.
Architecture
Domain Events
Domain Events

Domain Events Pattern
 Loose Coupling
business logic is separate from technology architecture. decouple
"What" From "How"
 Event-driven Architecture
asynchronous event-driven architectures
 Asynchronous Lazy-load
like lazy evaluation of functional language .
 True Scalability
Scale out on multi-core or multiple nodes using asynchronous message
passing ( JMS).

Example 1: Concurrency pattern
 No domain events codes ： CPU killer:
public int getMessageCount(){
int messageCount = xxxx; // complex computing, high CPU usage, CPU killer
return messageCount;
}
 Domain events can pre-load or pre-run the complex computing:
public int getMessageCount(DomainEvents domainEvents) {
if (messageCount == -1) {
if (messageCountAsyncResult == null) {
messageCountAsyncResult =
domainEvents.computeCount(account.getUserIdLong());
} else {
messageCount = (Integer)
messageCountAsyncResult.getEventResult();
}
}
return messageCount;
}

Example 2
Asynchronous Lazy load
1. invoking ‘getMessageCount’ will
send a message to
‘computeCount’ of Repository
by domainEvents.
2. again invoking
‘getMessageCount’ will return
last step result.(such as by
AJAX )
 Download Sample Source

Lazy initialization/Lazy evaluation
 On demand load or init a object from DB.
 functions are not evaluated until their results
are needed
 no Hibernate LazyInitializationExceptions
 no Open Session in View anti-pattern

Scale to distributed system
Domain
Model
JMS
MQ
ZeroQ
RabbitMQ
Persistence
Send Email
Other Services
Message
Domain
Model
Message
Distributed Cache
Distributed Cache

Events Challenge
 Most programmers are good at a synchronous
mode that be executed sequentially in a thread.
 Events is a non-blocking concurrent programming
mode, that maybe is harder to most people.
 if domain business need be executed
sequentially , so we can do it by domain events
too.

Blocking problem
 In a blocking system, wait thread is idle but
continue to consume system resources.
 This will very costs resource, for high transaction
volume:
the number of idle threads =(arrival_rate * processing_time)
the result can be a very big number if the
arrival_rate is high.
 Blocking system is running under a very ineffective
mode. No high throughout, no high CPU load.

Non-Blocking concurrent
 Make a call which returns a result. don't need to
use the result until at a much later stage of your
process.
 don't need to wait immediately after making the
call, instead you can proceed to do other things
until you reach the point where you need to use
the result.
 the call itself will return a "future" handle
immediately. The caller can go off doing other
things and later poll the "future" handle to see if
the response if ready.

JdonFramework
Non-Blocking concurrent
 Domain Model sends events to another
thread(a consumer) by RingBuffer in
Disruptor, so threads can communicates
through events.
 After consumer done, it will put the result in
another RingBuffer that publisher can read
or blocking read it, decided by business is
or not executed sequentially.

Higher abstract of concurrent
 Non-Blocking’s concurrent programming is complex.
 How to develop a concurrent app. easily?
 Like Actor Model
is like domain events, messages are sent asynchronously and non-
blocking in a “fire-and-forget” manner. But LMAX team of the Disruptor
thinks Actor model has bottleneck.
 DCI Architecture
DCI is easy to be understood. It’s abstract level is high than
domain events.

DCI
 DCI: Data, Context, Interactions is a
programming paradigm invented by Trygve
Reenskaug.
 keep our core model classes very thin.
 logic/behaviour should be kept in roles.
 Domain Events is a Interactions, Events
Producer is the Role.

Model Injection
 JdonFramework can inject Domain Events
into domain model at runtime, this is maybe
like Mixin.
 Domain Events is Interactions of Roles, so
Roles are then assigned(Injected) to data
objects at runtime, only when required
within given Context.

DCI ： Data
 Domain Model is the DATA of DCI, no logic
no behaviour.
Source: com.jdon.sample.test.domain.simplecase.MyModel

DCI : Role and Interactions
This is a Role of DCI ， it includes the
interactions of DCI. It is event producer
Source:com.jdon.sample.test.domain.simplecase.MyModelDomainEvent

DCI ： Context
 In Context,The Role will be injected
into the data.
 //after fetching the myModel object, it has been injected
events
 MyModel myModel = repository.getModel(new Long(100));
// call myModel’s events
 myModel .myModelDomainEvent.asyncFindName(this);

com.jdon.domain.dci.RoleAssigner
 com.jdon.domain.dci.RoleAssigner is a Role
assigner that can inject(Mixin) any interface
into a data model.
 When using RoleAssigner, it is not
necessary that fetch a object of data model
by a repository annotated with
@Introduce("modelCache") and its get
method with @Around

Different DCI styles
 If we already hold on a model object, we
can implements various functions by its
domain events,such as modify/update a
model.
 Otherwise:
 We create a context, and there we inject
events or functions into a new model object
by RoleAssigner,such as create or delete a
model.

client@Model
@Model client
Context
RoleAssigner
@Component@Component
Mixin
Create
ModifyEvent
@Component
@Component
inject

concurrent programming is easy
 Jdonframework makes an exploratory to
promote non-blocking concurrent
programming paradigm .
 DCI and Domain Events are different abstract
levels based concurrent programming .
 DCI and UML colors analysis method
can successfully docking, it is the highest level of
abstraction of business-oriented.
 Help most programmers quietly going to the way
of non-blocking concurrent programming when
they thinking in DDD.

DI and AOP
 Dependency Injection(DI or IOC)
@Service or @Component can inject with each other by class
construction(not supports setter injection).
@Service or @Component can be inected into @Model or by domain
events.
 Aspect-oriented programming(AOP)
with annotation @Introduce:
@Service or @Component can introduce each others as its
interceptor. @Model can introduce any POJO or @Component as its
interceptor.

@Model mechanism
Client
xx.getA(“a”)
A
@Model
Interceptor for A
with @Introduce
B that need
implements interface
and has @Introduce
Inject proxy of B
Interceptor for B
with @Introduce
Cache In-memeory
C
Inject proxy of c
Component
In Context
Container
interceptor

Inject a interceptor in @Model

Living space
 @Model lives in cache that default is Guava
Cache.
 @Component/@Service lives in a context
such as servletcontext.
 All @Component can be injected into
@Model.

@Component mechanism
Client
xx.getA(“a”)
A
@Service
Interceptor
(poincut=service)
B that need
implements interface
@Component
Inject proxy of B
Interceptor for B
with @Introduce
Context container (ServletContext)

@Service/@Component
 @Service("testService")
 public class TestServicePOJOImp implements TestService{
 private final UserRepository userRepository;
 public TestServicePOJOImp(UserRepository userRepository) {
 this.userRepository = userRepository;
 }
 }
 @Component()
 public class UserRepository {
 ….
 }
 Difference between @Service and @Component is that the @Service class
must have a interface then can be called by outside client beyond jdon.

@Service
 @Service expose to the client, has several kind instances: singleton ,
prototype or pool that have them annotations, default is
prototype(spring default is singleton ) 。

In-Memory Model
 When a domain model object with @Model is fetch
from repository, we need use
@Introduce(“modelCache”) to mak the object live
in memory.
 There are two cache interceptors existed before
and after domain layer.
 Domain events need annotation
@Introduce(“modelCache”) in the place that
domain model objects are created or
reconstructed from persistence or other systems.

JdonFramework Cache
Presentation
Domain Persistence
CacheInterceptor
In aspect.xml
DomainCacheInteceptor
@Introduce(“modelCache”)

in memeory model
@Introduce(“modelCache”) must be annotated in
the reposotory that @Model objects are created or
reconstructed This step is very important for domain events
working

What happeded in memeory?
 First times invoke “getModel” method of
RepositoryImp, jdon will do two things:
One: put the return value(model) in cache.
So next times can get it from cache.
Two: inject domain events into this model.
 Next times, invoke the method again, we will
get the model only one instance from cache.

Start jdonFramework in WEB
 If all is annotation, no jdonframework.xml,
no need this step
 Configuration in Web.xml:
 <context-param>
 <param-name> modelmapping-config </param-name>
 <param-value> jdonframework.xml </param-value>
 </context-param>
 <listener>
 <listener-
class>com.jdon.container.startup.ServletContainerListener</listener-class>
 </listener>

How to use in application
 AppUtil appUtil = new AppUtil();
 // xxx is value of @Service(“xxx”) annotation on class.
 XXXService xxxService = appUtil.getService(“xxx”);
 xxxService.method();
 If there is jdonframework.xml:
 AppUtil appUtil = new AppUtil("com.jdon.jdonframework.xml");

Other features
in JdonAccessory
 Rapid development, template toolkit. JDBC
template
 Eliminate “Controller/Action” ,No controller
code of MVC (only supports Struts 1.x)
 Batch Query, auto pagination 。

MVC Controller configuration
in jdonframework.xml(struts1.x)

Jdonframework MVC(struts1.x)
View
View
Controller
Jdonframework.xml
ActionForm Model
Service

Batch Query in jdon-jdbcTemp.jar
 Cache supports.
 Auto pagination.
 In presentation layer:
extends com.jdon.strutsutil.ModelListAction
 in persistence layer:
call getDatas of
com.jdon.controller.model.PageIterator

Jdon on Github
 https://github.com/banq/jdonframework
 http://en.jdon.com Document
 https://twitter.com/jdonframework
Twitter: @jdonframework

DDD Framework for Java: JdonFramework

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