What is a Jointpoint?
A joinpoint
is a point in the execution of the application where an aspect can be plugged
in. This point could be a method being called, an exception being thrown, or even
a field being modified. These are the points where your aspects code can be
inserted into the normal flow of your application to add new behavior.
What is an Advice?
Advice is the implementation of an
aspect. It is something like telling your application of a new behavior.
Generally, and advice is inserted into an application at joinpoints.
What is IOC (or Dependency Injection)?
The
basic concept of the Inversion of Control pattern (also known as dependency
injection) is that you do not create your objects but describe how they should
be created. You don’t directly connect your components and services together in
code but describe which services are needed by which components in a
configuration file. A container (in the case of the Spring
framework, the IOC container) is then responsible for hooking it all up.
i.e., Applying IoC, objects are given their dependencies at creation time by
some external entity that coordinates each object in the system. That is,
dependencies are injected into objects. So, IoC means an inversion of responsibility with regard
to how an object obtains references to collaborating objects.
What are the different types of IOC (dependency
injection) ?
There
are three types of dependency injection:
–> Constructor Injection (e.g. Pico
container, Spring etc): Dependencies are provided as constructor parameters.
–> Setter Injection (e.g. Spring):
Dependencies are assigned through JavaBeans properties (ex: setter methods).
–> Interface Injection (e.g. Avalon): Injection
is done through an interface.
Note: Spring supports only Constructor and Setter Injection
What are the benefits of IOC (Dependency Injection)?
Benefits
of IOC (Dependency Injection) are as follows:
Minimizes the amount of code in your application. With IOC containers you do
not care about how services are created and how you get references to the ones
you need. You can also easily add additional services by adding a new
constructor or a setter method with little or no extra configuration.
Make your application more testable by not requiring any singletons or JNDI
lookup mechanisms in your unit test cases. IOC containers make unit testing and
switching implementations very easy by manually allowing you to inject your own
objects into the object under test.
Loose coupling is promoted with minimal effort and least intrusive mechanism.
The factory design pattern is more intrusive because components or services
need to be requested explicitly whereas in IOC the dependency is injected into
requesting piece of code. Also some containers promote the design to interfaces
not to implementations design concept by encouraging managed objects to
implement a well-defined service interface of your own.
IOC containers support eager instantiation and lazy loading of services.
Containers also provide support for instantiation of managed objects, cyclical
dependencies, life cycles management, and dependency resolution between managed
objects etc.
What is Spring ?
Spring
is an open source framework created to address the complexity of enterprise
application development. One of the chief advantages of the Spring framework is
its layered architecture, which allows you to be selective about which of its
components you use while also providing a cohesive framework for J2EE
application development.
What
are the advantages of Spring framework?
The
advantages of Spring are as follows:
–> Spring has layered architecture. Use what you need and leave you don’t
need now.
–> Spring Enables POJO Programming. There
is no behind the scene magic here. POJO programming enables continuous
integration and testability.
–> Dependency Injection and Inversion of
Control Simplifies JDBC
–> Open source and no vendor lock-in.
What are features of Spring ?
Lightweight:
spring is lightweight when it comes to size and transparency. The basic version
of spring framework is around 1MB. And the processing overhead is also very
negligible.
Inversion
of control (IOC):
Loose coupling is achieved in spring using the technique Inversion of Control.
The objects give their dependencies instead of creating or looking for
dependent objects.
Aspect
oriented (AOP):
Spring supports Aspect oriented programming and enables cohesive development by
separating application business logic from system services.
Container:
Spring contains and manages the life cycle and configuration of application
objects.
MVC
Framework:
Spring comes with MVC web application framework, built on core Spring
functionality. This framework is highly configurable via strategy interfaces,
and accommodates multiple view technologies like JSP, Velocity, Tiles, iText, and POI. But other frameworks can be easily used
instead of Spring MVC Framework.
Transaction
Management:
Spring framework provides a generic abstraction layer for transaction management.
This allowing the developer to add the pluggable transaction
managers, and making it easy to demarcate transactions without dealing with
low-level issues. Spring’s transaction support is not tied to J2EE
environments and it can be also used in container less environments.
JDBC
Exception Handling:
The JDBC abstraction layer of the Spring offers a meaningful exception
hierarchy, which simplifies the error handling strategy. Integration with
Hibernate, JDO, and iBATIS: Spring provides best
Integration services with Hibernate, JDO and iBATIS
How many modules are
there in Spring? What
are they?
Spring comprises of seven modules. They are..
The
core container:
The core container provides the essential functionality of the Spring
framework. A primary component of the core container is the BeanFactory,
an implementation of the Factory pattern. The BeanFactory
applies the Inversion of Control (IOC) pattern to separate an application’s
configuration and dependency specification from the actual application code.
Spring
context:
The Spring context is a configuration file that provides context information to
the Spring framework. The Spring context includes
enterprise services such as JNDI, EJB, e-mail, internalization, validation, and
scheduling functionality.
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