spring technology
[
attachment=16011]
Background
There are several types of springs. One of the most common consists of wire wound into a cylindrical or conical shape. An extension spring is a coiled spring whose coils normally touch each other; as a force is applied to stretch the spring, the coils separate. In contrast, a compression spring is a coiled spring with space between successive coils; when a force is applied to shorten the spring, the coils are pushed closer together. A third type of coiled spring, called a torsion spring, is designed so the applied force twists the coil into a tighter spiral. Common examples of torsion springs are found in clipboards and butterfly hair clips.
History
Very simple, non-coil springs have been used throughout history. Even a resilient tree branch can be used as a spring. More sophisticated spring devices date to the Bronze Age, when eyebrow tweezers were common in several cultures. During the third century B.C., Greek engineer Ctesibius of Alexandria developed a process for making "springy bronze" by increasing the proportion of tin in the copper alloy, casting the part, and hardening it with hammer blows. He attempted to use a combination of leaf springs to operate a military catapult, but they were not powerful enough. During the second century B.C., Philo of Byzantium, another catapult engineer, built a similar device, apparently with some success. Padlocks were widely used in the ancient Roman empire, and at least one type used bowed metal leaves to keep the devices closed until the leaves were compressed with keys.
Raw Materials
Steel alloys are the most commonly used spring materials. The most popular alloys include high-carbon (such as the music wire used for guitar strings), oil-tempered low-carbon, chrome silicon, chrome vanadium, and stainless steel.
Other metals that are sometimes used to make springs are beryllium copper alloy, phosphor bronze, and titanium. Rubber or urethane may be used for cylindrical, non-coil springs. Ceramic material has been developed for coiled springs in very high-temperature environments. One-directional glass fiber composite materials are being tested for possible use in springs.
Design
Various mathematical equations have been developed to describe the properties of springs, based on such factors as wire composition and size, spring coil diameter, the number of coils, and the amount of expected external force. These equations have been incorporated into computer software to simplify the design process.
Quality Control
Various testing devices are used to check completed springs for compliance with specifications. The testing devices measure such properties as the hardness of the metal and the amount of the spring's deformation under a known force. Springs that do not meet the specifications are discarded. Statistical analysis of the test results can help manufacturers identify production problems and improve processes so fewer defective springs are produced.
spring technology
Introduction
In early 2004, Martin Fowler asked the readers of his site: when talking about Inversion of Control: “the
question is, what aspect of control are [they] inverting?”. Fowler then suggested renaming the principle
(or at least giving it a more self-explanatory name), and started to use the term Dependency Injection. His
article then continued to explain the ideas underpinning the Inversion of Control (IoC) and Dependency
Injection (DI) principle.
If you need a decent insight into IoC and DI, please do refer to said article :
Java applications (a loose term which runs the gamut from constrained applets to full-fledged n-tier server-side
enterprise applications) typically are composed of a number of objects that collaborate with one another to form
the application proper. The objects in an application can thus be said to have dependencies between themselves.
The Java language and platform provides a wealth of functionality for architecting and building applications,
ranging all the way from the very basic building blocks of primitive types and classes (and the means to define
new classes), to rich full-featured application servers and web frameworks. One area that is decidedly
conspicuous by its absence is any means of taking the basic building blocks and composing them into a
coherent whole; this area has typically been left to the purvey of the architects and developers tasked with
building an application (or applications). Now to be fair, there are a number of design patterns devoted to the
business of composing the various classes and object instances that makeup an all-singing, all-dancing
application. Design patterns such as Factory, Abstract Factory, Builder, Decorator, and Service Locator (to
name but a few) have widespread recognition and acceptance within the software development industry
(presumably that is why these patterns have been formalized as patterns in the first place). This is all very well,
but these patterns are just that: best practices given a name, typically together with a description of what the
pattern does, where the pattern is typically best applied, the problems that the application of the pattern
addresses, and so forth. Notice that the last paragraph used the phrase “... a description of what the pattern
does...”; pattern books and wikis are typically listings of such formalized best practice that you can certainly
take away, mull over, and then implement yourself in your application.
The IoC component of the Spring Framework addresses the enterprise concern of taking the classes, objects,
and services that are to compose an application, by providing a formalized means of composing these various
disparate components into a fully working application ready for use. The Spring Framework takes best
practices that have been proven over the years in numerous applications and formalized as design patterns, and
actually codifies these patterns as first class objects that you as an architect and developer can take away and
integrate into your own application(s). This is a Very Good Thing Indeed as attested to by the numerous
organizations and institutions that have used the Spring Framework to engineer robust, maintainable
applications.
1.1. Overview
The Spring Framework contains a lot of features, which are well-organized in six modules shown in the
diagram below. This chapter discusses each of the modules in turn.
Spring Framework (2.5.6) 16
Overview of the Spring Framework
The Core package is the most fundamental part of the framework and provides the IoC and Dependency
Injection features. The basic concept here is the BeanFactory, which provides a sophisticated implementation
of the factory pattern which removes the need for programmatic singletons and allows you to decouple the
configuration and specification of dependencies from your actual program logic.
The Context package build on the solid base provided by the Core package: it provides a way to access objects
in a framework-style manner in a fashion somewhat reminiscent of a JNDI-registry. The context package
inherits its features from the beans package and adds support for internationalization (I18N) (using for example
resource bundles), event-propagation, resource-loading, and the transparent creation of contexts by, for
example, a servlet container.
The DAO package provides a JDBC-abstraction layer that removes the need to do tedious JDBC coding and
parsing of database-vendor specific error codes. Also, the JDBC package provides a way to do programmatic as
well as declarative transaction management, not only for classes implementing special interfaces, but for all
your POJOs (plain old Java objects).
The ORM package provides integration layers for popular object-relational mapping APIs, including JPA, JDO,
Hibernate, and iBatis. Using the ORM package you can use all those O/R-mappers in combination with all the
other features Spring offers, such as the simple declarative transaction management feature mentioned
previously.
Spring's AOP package provides an AOP Alliance-compliant aspect-oriented programming implementation
allowing you to define, for example, method-interceptors and pointcuts to cleanly decouple code implementing
functionality that should logically speaking be separated. Using source-level metadata functionality you can
also incorporate all kinds of behavioral information into your code, in a manner similar to that of .NET
attributes.
Spring's Web package provides basic web-oriented integration features, such as multipart file-upload
functionality, the initialization of the IoC container using servlet listeners and a web-oriented application
context. When using Spring together with WebWork or Struts, this is the package to integrate with.
Spring's MVC package provides a Model-View-Controller (MVC) implementation for web-applications.
Spring's MVC framework is not just any old implementation; it provides a clean separation between domain
model code and web forms, and allows you to use all the other features of the Spring Framework.
1.2. Usage scenarios
With the building blocks described above you can use Spring in all sorts of scenarios, from applets up to
fully-fledged enterprise applications using Spring's transaction management functionality and web framework
integration.
Spring Framework (2.5.6) 18
Typical full-fledged Spring web application
By using Spring's declarative transaction management features the web application is fully transactional, just as
it would be when using container managed transactions as provided by Enterprise JavaBeans. All your custom
business logic can be implemented using simple POJOs, managed by Spring's IoC container. Additional
services include support for sending email, and validation that is independent of the web layer enabling you to
choose where to execute validation rules. Spring's ORM support is integrated with JPA, Hibernate, JDO and
iBatis; for example, when using Hibernate, you can continue to use your existing mapping files and standard
Hibernate SessionFactory configuration. Form controllers seamlessly integrate the web-layer with the domain
model, removing the need for ActionForms or other classes that transform HTTP parameters to values for your
domain model.
Spring middle-tier using a third-party web framework
Sometimes the current circumstances do not allow you to completely switch to a different framework. The
Spring Framework (2.5.6) 19
Spring Framework does not force you to use everything within it; it is not an all-or-nothing solution. Existing
front-ends built using WebWork, Struts, Tapestry, or other UI frameworks can be integrated perfectly well with
a Spring-based middle-tier, allowing you to use the transaction features that Spring offers. The only thing you
need to do is wire up your business logic using an ApplicationContext and integrate your web layer using a
WebApplicationContext.
Remoting usage scenario
When you need to access existing code via web services, you can use Spring's Hessian-, Burlap-, Rmi- or
JaxRpcProxyFactory classes. Enabling remote access to existing applications suddenly is not that hard
anymore.
EJBs - Wrapping existing POJOs
The Spring Framework also provides an access- and abstraction- layer for Enterprise JavaBeans, enabling you
to reuse your existing POJOs and wrap them in Stateless Session Beans, for use in scalable, failsafe web
applications that might need declarative security.
spring technology
[
attachment=21082]
What does Spring provide?
Lightweight container and framework
Most of your code will be unaware of the Spring framework
Use only the parts you of Spring you want
Manages dependencies between your objects
Encourages use of interfaces
Lessens “coupling” between objects
Cleaner separation of responsibilities
Put logic that applies to many objects in one single place
Separate the class’s core responsibility from other duties
Simplifies database integration
Spring JDBC
Hibernate
iBATIS
Java Persistence
Example Application
Contacts – store and retrieve contacts
Created using MyEclipse 7
Uses Maven 2 to manage libraries
Demonstrates basic Spring capabilities
Contact has a Person, collection of Email, and collection of Phone objects
Can use an XML file or database as repository
User interface is via the console
See READ_ME file under project folder
External Configuration
Configuration options
Properties files
XML configuration files
Annotations
XML Configuration
Specify the creation of objects
Specify the dependencies between objects
Implementing AOP in Spring
Advice
Several different ways to configure Advice objects
Implement interfaces and XML configuration
Use @AspectJ annotations
Integrate with AspectJ
Advice is commonly applied to a method
Different ways to apply advice to an object
Before advice
After returning advice
After throwing advice
After advice
Around advice