FAQ: Why have an alternative to Spring?
What is the difference
The purpose of Spring is to make JEE simpler. The purpose of Essence is to
make JSE simpler.
Spring encourages bottom up design by constructing small components and in turn
constructing larger components, until finally you have a complete system. Using
XML configuration you tend to get lengthy files describing every level of the
application. Components can wire themselves so the configuration has but a
subset of dependencies in it. Spring does not have direct support of
binding components to a thread.
Essence encourages top down design. This is harder initially as you need to have
a partial design to start with. The application is structured as a collection of single
threaded logical processes. Each logical process has a number of stateless
business components which communicate between shared data collections or
messaging.
Infrastructure components are hidden or simplified by the infrastructure so
configuration should only show high level components.
This is the configuration file for a custom JMS broker with durable queues and
topics with clustering support.
jms-broker.config This file describes all the components, their
dependencies, where state resides, how it is structured and what
persistence/failover is used. It is about 38 lines long. For comparison this is
the client
jms-client.config
Spring tries hard not to change the way developers develop. This is because Spring
attempts to serve the broadest range of uses and not discourage developers from
using it. This also suits rapid prototyping which often gets something working
quickly. However having a well designed, maintainable application means
you have to go beyond rapid prototyping to a more controlled and well understood
system.
Essence encourages a set of best practices for thread and component
configuration and enforces them. Essence
attempts to describe all references in the configuration file. References
between components and all properties are managed by the container. This way you
can be sure all dependencies between components and properties are described in
the configuration file as the container discourages you to obtaining them via
other means. As all processes are single threaded, components can refer to each
other without concerns for thread safety or context switching however the
container does allow references to single threaded components between processes.
Multi-threaded logical processes are also supported. All components in
that logical process are required to be thread safe. However you can mix
single threaded and multi threaded logical processes and only the components in
the multi-threaded logical processes need be thread safe.
Essence separates business logic from state. Business components should be
logically stateless. All state can be stored in collections of immutable
objects. This makes sharing state between processes and JVMs transparent
are simple to visualise. An application can be made durable by backing all it
state to disk or a second or four servers (or both) and restarting the
application reloads the state. Essence provides this for you through a few
lines of configuration.
J2EE has Dao (Data Access Objects) which tend to involve a lot of custom code.
Essence has a java.util.Map which can also be viewed as a java.util.Queue. A
callback can be added to hear events. Helper methods allow you to searches,
joins and perform other complex operations on a Map.
J2EE/Spring/Hibernate has Java Persistence API, JdbcTemplates, Hibernate
configuration files and annotations. Essence has a java.util.Map (which has been
configured to be persistent, and/or distributed/clustered without code changes.)
J2EE/Spring supports JMS messaging, Essence has implicit messages via a Queue or
Map you can add a Callback to hear new messages/events.
J2EE/Spring has complex deployment descriptors and an assortment of
configuration files. Essence has one configuration which configures components,
messaging, clusters, collections.
J2EE/Spring has an enormous number of classes which you could use. An
application in Essence can be written without a single reference to a class,
interface or annotation or import for an Essence class.
Sun's J2EE App Server with Spring is around 300 MB. The sample application
Essence JMS with the framework, broker and client is 612 KB.
Could you use Essence and Spring together?
Yes. Essence is best at describing the high level system. Essence attempts to hide away low level infrastructure. Spring can
describe every level object in the system and has integration for many systems which makes it a good choice.
