|By Paul Hammant||
|December 4, 2003 12:00 AM EST||
Inversion of Control (IoC) is about software components doing what they are told, when they are told. Your OO application could well become unmaintainable without it.
IoC is a pattern that helps teams avoid the dependency hell that results when an application grows into a large pseudo-platform without taking care to adequately decouple logic; that thing that ultimately only a couple of its omnipotent architects or old-lag premium-rate contractors really understand; that system that Heath Robinson and Rube Goldberg might have made together (look them up).
The problem with small working applications that become large is that static-method entanglement does not scale. One part of a system that's otherwise fairly self-contained statically accesses another part of the system and cannot be instantiated without invoking methods in the latter. Thus it can't easily be isolated for unit testing. What's more, it can't be developed as an independent component. Components that are developed separately can have their own development teams and may well be part of a larger design. These components will have their own source control directory and can be developed against mock implementations of their dependent components. All this will help overall development become faster, in terms of both the team's efficiency and the build time.
As an example, let's take a Personal Information Manager (PIM) application that has UI and persistence elements. The naïve implementation might have inline JDBC statements among graphical code. A componentized application would have that persistence logic separated into a persistence component with user interface logic enshrined in a view-controller component. Clearly, if the two teams developing their respective components agree on a slowly evolving interface/implementation-separated API for persistence, they can develop at their own pace and ship versions of their components whenever it's appropriate.
A third piece, which is not a component, would be the bootstrap for the application. That bootstrap may well be entirely contained in a static main method of a simple class and would merely instantiate the two components, passing one into the other's constructor before invoking setVisible(true) or similar. With the introduction of this bootstrap we can see the control aspect of the IoC pattern.
In a noncomponentized version of our example, the view-controller may well have its own main method, might instantiate a fixed version of the PIM store, or access it via an unnecessary singleton factory (public static methods are generally bad), i.e., the control is very much inside the component in question.
The word "inversion" from the pattern name is about getting control back. The containing application (often a true container or a proper framework rather than a main method) controls when a component is instantiated and which implementations of its dependent components it is passed.
IoC also dictates the configuration of components. A JDBC version of the PIM store above would clearly require some JDBC settings. Classically, developers may write a mechanism to retrieve them from a fixed properties file. IoC would insist that the configuration is passed into the component. In our hypothetical example, it would take it via the constructor and be interface/implementation separated. Thus the configuration is a component. It would be tightly coupled to the component that requires it, but subject to multiple implementations, one of which may be the "from properties file".
Inversion of Control has moved to the center stage in the last six months after a five-year gestation period. There are three types of Inversion of Control. Type 1 uses configuration data (Avalon, JContainer); Type 2 uses bean introspection (Spring Framework, WebWork2, HiveMind); Type 3 uses constructor signatures (PicoContainer).
For a componentized system that uses singletons or similar for component resolution, the dependency is obscure. In IoC it is declarative. The application would have loosely coupled components and be more scalable, more maintainable, and more testable. It's a very small investment for a very large return. Inversion of Control rocks.
|Eric Herman 12/09/03 08:40:08 PM EST|
I''m glad that this subject is getting some more attention and we''re starting to think a bit more about it. My experiences have taught me to think of the use of static variables and static methods as a hint that I need to be thinking more about design. I''m not sure that the name "Inversion of Control" communicates the issue, but I don''t have a better name. I often use the phase "statics hurt" when talking about design. If possible, see if statics can be avoided entirely in your application. If not, how close can we get? Maybe we can hold a reference to a instance (which we can then mock out for testing) rather than use a static? Maybe a ThreadLocal can help? And who knows, maybe we''ll start to see some possibilities for polymorphism or plugabillity that were previously unavailable to us?
|Rob 12/06/03 08:03:22 PM EST|
IoC rocks indeed! (and also nice to know there''s actually a name for what i''ve been doing :-)
|Juergen Hoeller 12/05/03 08:13:18 AM EST|
FYI: Since 1.0 M3, the Spring Framework''s bean factory supports both Type 2 IoC (bean property resolution) and Type 3 IoC (constructor resolution).
|Juergen Hoeller 12/05/03 08:13:12 AM EST|
FYI: Since 1.0 M3, the Spring Framework''s bean factory supports both Type 2 IoC (bean property resolution) and Type 3 IoC (constructor resolution).
Microservices are a very exciting architectural approach that many organizations are looking to as a way to accelerate innovation. Microservices promise to allow teams to move away from monolithic "ball of mud" systems, but the reality is that, in the vast majority of organizations, different projects and technologies will continue to be developed at different speeds. How to handle the dependencies between these disparate systems with different iteration cycles? Consider the "canoncial problem" in this scenario: microservice A (releases daily) depends on a couple of additions to backend B (re...
Nov. 27, 2015 01:00 AM EST Reads: 418
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Day 2 Keynote at 17th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, wil...
Nov. 27, 2015 01:00 AM EST Reads: 539
PubNub has announced the release of BLOCKS, a set of customizable microservices that give developers a simple way to add code and deploy features for realtime apps.PubNub BLOCKS executes business logic directly on the data streaming through PubNub’s network without splitting it off to an intermediary server controlled by the customer. This revolutionary approach streamlines app development, reduces endpoint-to-endpoint latency, and allows apps to better leverage the enormous scalability of PubNub’s Data Stream Network.
Nov. 27, 2015 01:00 AM EST Reads: 293
The cloud. Like a comic book superhero, there seems to be no problem it can’t fix or cost it can’t slash. Yet making the transition is not always easy and production environments are still largely on premise. Taking some practical and sensible steps to reduce risk can also help provide a basis for a successful cloud transition. A plethora of surveys from the likes of IDG and Gartner show that more than 70 percent of enterprises have deployed at least one or more cloud application or workload. Yet a closer inspection at the data reveals less than half of these cloud projects involve production...
Nov. 27, 2015 01:00 AM EST Reads: 447
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Ben Perlmutter, a Sales Engineer with IBM Cloudant, demonstrated techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, faster user experience, both offline and online. The focus of this talk was on IBM Cloudant, Apache CouchDB, and ...
Nov. 27, 2015 12:45 AM EST Reads: 392
Container technology is shaping the future of DevOps and it’s also changing the way organizations think about application development. With the rise of mobile applications in the enterprise, businesses are abandoning year-long development cycles and embracing technologies that enable rapid development and continuous deployment of apps. In his session at DevOps Summit, Kurt Collins, Developer Evangelist at Built.io, examined how Docker has evolved into a highly effective tool for application delivery by allowing increasingly popular Mobile Backend-as-a-Service (mBaaS) platforms to quickly crea...
Nov. 27, 2015 12:00 AM EST Reads: 332
I recently attended and was a speaker at the 4th International Internet of @ThingsExpo at the Santa Clara Convention Center. I also had the opportunity to attend this event last year and I wrote a blog from that show talking about how the “Enterprise Impact of IoT” was a key theme of last year’s show. I was curious to see if the same theme would still resonate 365 days later and what, if any, changes I would see in the content presented.
Nov. 26, 2015 10:00 PM EST Reads: 392
Cloud computing delivers on-demand resources that provide businesses with flexibility and cost-savings. The challenge in moving workloads to the cloud has been the cost and complexity of ensuring the initial and ongoing security and regulatory (PCI, HIPAA, FFIEC) compliance across private and public clouds. Manual security compliance is slow, prone to human error, and represents over 50% of the cost of managing cloud applications. Determining how to automate cloud security compliance is critical to maintaining positive ROI. Raxak Protect is an automated security compliance SaaS platform and ma...
Nov. 26, 2015 04:00 PM EST Reads: 382
Internet of @ThingsExpo, taking place June 7-9, 2016 at Javits Center, New York City and Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 18th International @CloudExpo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo New York Call for Papers is now open.
Nov. 26, 2015 03:30 PM EST Reads: 525
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo 2016 in New York and Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound cha...
Nov. 26, 2015 03:15 PM EST Reads: 521
We are rapidly moving to a brave new world of interconnected smart homes, cars, offices and factories known as the Internet of Things (IoT). Sensors and monitoring devices will touch every part of our lives. Let's take a closer look at the Internet of Things. The Internet of Things is a worldwide network of objects and devices connected to the Internet. They are electronics, sensors, software and more. These objects connect to the Internet and can be controlled remotely via apps and programs. Because they can be accessed via the Internet, these devices create a tremendous opportunity to inte...
Nov. 26, 2015 02:15 PM EST Reads: 499
Today air travel is a minefield of delays, hassles and customer disappointment. Airlines struggle to revitalize the experience. GE and M2Mi will demonstrate practical examples of how IoT solutions are helping airlines bring back personalization, reduce trip time and improve reliability. In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect with GE, and Dr. Sarah Cooper, M2Mi’s VP Business Development and Engineering, explored the IoT cloud-based platform technologies driving this change including privacy controls, data transparency and integration of real time context with p...
Nov. 26, 2015 01:00 PM EST Reads: 392
We all know that data growth is exploding and storage budgets are shrinking. Instead of showing you charts on about how much data there is, in his General Session at 17th Cloud Expo, Scott Cleland, Senior Director of Product Marketing at HGST, showed how to capture all of your data in one place. After you have your data under control, you can then analyze it in one place, saving time and resources.
Nov. 26, 2015 12:00 PM EST Reads: 151
The Internet of Things (IoT) is growing rapidly by extending current technologies, products and networks. By 2020, Cisco estimates there will be 50 billion connected devices. Gartner has forecast revenues of over $300 billion, just to IoT suppliers. Now is the time to figure out how you’ll make money – not just create innovative products. With hundreds of new products and companies jumping into the IoT fray every month, there’s no shortage of innovation. Despite this, McKinsey/VisionMobile data shows "less than 10 percent of IoT developers are making enough to support a reasonably sized team....
Nov. 26, 2015 11:00 AM EST Reads: 445
Just over a week ago I received a long and loud sustained applause for a presentation I delivered at this year’s Cloud Expo in Santa Clara. I was extremely pleased with the turnout and had some very good conversations with many of the attendees. Over the next few days I had many more meaningful conversations and was not only happy with the results but also learned a few new things. Here is everything I learned in those three days distilled into three short points.
Nov. 26, 2015 10:00 AM EST Reads: 290
DevOps is about increasing efficiency, but nothing is more inefficient than building the same application twice. However, this is a routine occurrence with enterprise applications that need both a rich desktop web interface and strong mobile support. With recent technological advances from Isomorphic Software and others, rich desktop and tuned mobile experiences can now be created with a single codebase – without compromising functionality, performance or usability. In his session at DevOps Summit, Charles Kendrick, CTO and Chief Architect at Isomorphic Software, demonstrated examples of com...
Nov. 26, 2015 09:45 AM EST Reads: 370
As organizations realize the scope of the Internet of Things, gaining key insights from Big Data, through the use of advanced analytics, becomes crucial. However, IoT also creates the need for petabyte scale storage of data from millions of devices. A new type of Storage is required which seamlessly integrates robust data analytics with massive scale. These storage systems will act as “smart systems” provide in-place analytics that speed discovery and enable businesses to quickly derive meaningful and actionable insights. In his session at @ThingsExpo, Paul Turner, Chief Marketing Officer at...
Nov. 26, 2015 09:30 AM EST Reads: 379
In his keynote at @ThingsExpo, Chris Matthieu, Director of IoT Engineering at Citrix and co-founder and CTO of Octoblu, focused on building an IoT platform and company. He provided a behind-the-scenes look at Octoblu’s platform, business, and pivots along the way (including the Citrix acquisition of Octoblu).
Nov. 26, 2015 09:00 AM EST Reads: 479
In his General Session at 17th Cloud Expo, Bruce Swann, Senior Product Marketing Manager for Adobe Campaign, explored the key ingredients of cross-channel marketing in a digital world. Learn how the Adobe Marketing Cloud can help marketers embrace opportunities for personalized, relevant and real-time customer engagement across offline (direct mail, point of sale, call center) and digital (email, website, SMS, mobile apps, social networks, connected objects).
Nov. 26, 2015 08:45 AM EST Reads: 270
The Internet of Everything is re-shaping technology trends–moving away from “request/response” architecture to an “always-on” Streaming Web where data is in constant motion and secure, reliable communication is an absolute necessity. As more and more THINGS go online, the challenges that developers will need to address will only increase exponentially. In his session at @ThingsExpo, Todd Greene, Founder & CEO of PubNub, exploreed the current state of IoT connectivity and review key trends and technology requirements that will drive the Internet of Things from hype to reality.
Nov. 26, 2015 06:45 AM EST Reads: 406