Naturally working on a lot of web application projects in multiple languages from Java EE to PHP to websites to mobile applications, one common thing that we see time and time again is the lack of thought that goes into design patterns for websites and web applications. Often having to pick up projects at this point, generally when they have already gone seriously wrong, we can’t but help think that there must be a better way to prevent these issues we see through sharing best practices to ensure scalable web applications are built and can be maintained with ease. Specifically for this blog post we are going to look at the Model View Controller MVC design pattern.
If you are working in any form of software development, website development or web application development, I’d argue that this is one of the most powerful design patterns to get your head around as when you fully understand the relatively simple approach behind the MVC design pattern this allows you to think about the structure of your code and project before jumping in and writing a single line of code. By taking this time up front, I can absolutely guarantee that this will save you an unbelievable amount of time working on your application over time and most importantly, for the businesses you are working with this will help to ensure bugs, features, functionality improvements and tweaks can be delivered much faster with fewer errors.
What is the Model View Controller MVC Design Pattern
So let’s just take things back a step as if you haven’t been working away on larger web application projects previously, you may not even be aware of the MVC design pattern, hopefully you are away of what design patterns actually are if you are working in web application development though, if not, then I recommend going on a date with Amazon to learn about design patterns.
The MVC design pattern is a way of structuring your code to break up the key elements of your web application which includes;
- Model: These are the bits of code that actually do things
- View: These are the bits of code that make the things look pretty
- Controller: These are the bits of code that control what happens when someone requests a resource such as a page on your website, the business logic of your web application
Ok, so it’s a little more complex than that in the background, but that is MVC explained in the simplest way. I’m not going to talk about the theory of MVC to the n’th degree, instead I’m going to look at the practicalities of MVC while dabbling into the Single Responsibility Principle design pattern and how the two link together extremely well.
For the purposes of this blog post, we are going to focus on Java as the programming language to highlight this concept as Java is better than PHP. Fact (in my opinion). 😉 (cue the haters…). On a serious note though the reason why we’re looking at Java for this example is because it is more suited to using a structured MVC design pattern for projects than PHP is, on the whole, which is due to the separation of the Model (Java classes), the View (JSPs) and the Controller (Java Servlets) which link in nicely together. For the same MVC setup in PHP you will probably be looking at something like the Zend Framework which has been designed to focus around an MVC architecture. With that understanding, let’s look at the practicalities of MVC and why this is such an awesome design pattern that you really need to be using.
Benefits of the MVC Design Pattern
Before we jump into a few simple examples of using the Model View Controller MVC design pattern, lets first just look at why this is such an awesome design pattern and why you should seriously consider using this for a variety of the web application projects you are working on.
Separation of Concerns
Being able to separate the key parts of your web application into the Model, the View and the Controller is an extremely efficient way of working. Being able to separate out the key functionality within your application from the business logic from your application and separating the visual and layout side of your application means that you can clearly focus on the task at hand and work effectively throughout your code.
Focused Developers and Niche Sill Sets
This also allows updates to various points within your web application without impacting the other aspects. For example, you can quite simply make changes to your user interface without impacting the business logic within your application. This is an extremely powerful setup to allow your web application to be modified with ease.
Parallel Development across Multiple Teams
As your web applications grows, multiple teams of developers will be working on your application code base to enhance features and functionality. By using a true MVC design pattern, this allows multiple people to work on your code base with ease.
As your web application grows using a non-MVC design pattern, you will soon reach the point whereby developers are struggling to work on a project without impacting the work of another developer, to the point whereby this may actually restrict the amount of work that can be completed during any given time scale. This is not a good position to be in and if you reach this point, you will soon see how much more efficient the MVC design pattern really is.
MVC in Practice
Within Java, you have your deployment descriptor which is designed to control how requests are handled when a user types in a URL on your website. For example, when someone visits www.example.com/login/ the web.xml file will send the request on to the Controller file named Login.java in this example;
The Controller – Login.java
Taking this example, the Controller is just a standard Java Servlet which is designed to handle the incoming request and control whatever you want to do with these requests. For example, and keeping things basic, on a login page a user may have been redirected to this page after trying to access a restricted resource and it would be nice to redirect the user back to the page they were trying to access instead of to a generic login landing page;
The concept of the Controller is designed to take care of the business logic part of the web application so you can build in the logic you require whilst keeping the key functionality separate. This is hugely important as this means that as the development team grows one team can be working on the business logic while another team can be working on the key functionality without impacting the workflow of either team. The above example is purely the Controller which then forwards the request onto the JSP to provide the View aspect of the process, but we have missed one key aspect, the Model. In the example above there are no calls to and Model classes designed to pull in key data, so let’s look at an example where the Model is used before we look at the View part of the process.
So let’s imagine that whenever somebody accesses the login page, an email is sent to someone. You would never do this in practice as this is just pointless, but this highlights the concept of the Model. In the same context and looking at something more practical, you would use the Model to retrieve some data from the database such as a snippet of text for example which is controlled by a content management system type setup. Never the less, we’ll use this as an example.
The functionality to send an email has been broken out into its own class designed to break out the business logic which is “When someone views the login page, send an email” from the actual functionality for sending an email.
The Model – SendEmail.java
Looking specifically at the Model class, this is designed to actually implement the core functionality that you require. In this example send an email. From here, you can control specific functionality and separate this functionality completely away from the business logic of the application. Here helps you to work more efficiently by building up a solid and scalable library of core functionality that drives your web application rather than just simply working with a system which contains highly coupled code.
Taking this example beyond the simple SendEmail() functionality which is purely focused on completing a specific action in the background, another more specific example would be to collect data from the database which is then sent on to the View which is for the user to see who has requested the original resource. For example, taking the MVC web application to the perfect situation whereby every single aspect of content is purely database driven, the result would be a Model class along the lines of getMetaTitle(url) which is designed for the Controller to generate the correct meta data for the page that has been requested.
The Model classes are where the real power lies within your web application. Here lies the true power of how your web application implements the cool features and functionality throughout the entire system. The Controller allows you to do exactly that, control how the Models are pieced together when a specific URL is requested which allows you to create the fantastic experience for your website visitors.
The View – Login.jsp
So let’s look at a more practical example whereby you have used a Model class to retrieve some data from the database for what the HTML H1 should be. Once you have received this data in the Controller Servlet you need to then add this data to the Request object so that this can then be retrieved by the View JSP;
As can be seen in the code above from the Controller Servlet, setting the attribute for the data that you wish to pass to the View is the next step in the process. From here, now let’s look at the View part of the MVC design pattern to look at how to retrieve this data in a safe way.
Here we can take a look at the View, login.jsp, which is designed to handle the visual side of the web application. From here you have the ability to retrieve data passed to the View from the Controller and there are several ways of doing this.
At the most basic level, you can use a small scriptlet such as;
<%= request.getAttribute(“htmlH1”) %>
Which is will output the data contained within the stored attribute named “htmlH1”. So if you wanted to wrap this in a H1 tag then this would look as follows within the JSP;
<h1><%= request.getAttribute(“htmlH1”) %></h1>
Simple and effective. The problem here though is that as your web application scales, particularly on an international level, this isn’t the best approach to take as there can be a variety of differences for different locales such as time and date formatting along with currency formatting etc. So lets look at how best to handle requesting data from the Request object and displaying this within the View JSP through the use of the Java Standard Tag Library, JSTL.
JSTL has been designed to be a more user friendly way of displaying content within the JSP without the need for using scriptlets which should never really be used if possible. With JSTL the tags used will look very similar to any web developer who has been using HTML for a while. They follow the same logic with tags and attributes, the difference being is that JSTL is designed to apply common activities to JSPs such as simple items including displaying some content such as the HTML H1 tag content or something more advanced such as a For or While loop. Below follows on form the basic example given already, with the use of displaying the HTML H1 tag on the page;
Here there are a few things to point out to understand what is happening. Firstly, there are two lines at the top which allow you to use the full power of JSTL which are;
<%@ taglib prefix=”c” uri=”http://java.sun.com/jsp/jstl/core” %>
<%@ taglib uri=”http://java.sun.com/jsp/jstl/functions” prefix=”fn” %>
The first line is for using the Core JSTL functionality, while the second line is to use the JSTL functions for things such as data manipulation. In this example, we’re only going to need the core functionality. So is you notice the section for displaying the HTML H1 tag is as follows;
The <c: prefix in the code above is telling the JSP to use the JSTL Core functionality which was referenced previously in the page. Next this is telling JSTL to display the contents contained within the attribute named “htmlH1” which we set previously in the Controller Servlet. So that when you look at this on the original Login page you just requested then you see this information as you would expect;
Sounds simple, right? Well, yes, it actually is extremely simple to use a Model View Controller MVC design pattern when you think through the structure of your code instead of just jumping in and writing code. The difference being is that when you stop to think about the design pattern that you are using within your web application that you can quite easily make huge improvements both now and in the future. The Model View Controller MVC design patter is just one of many extremely powerful design patterns that you should seriously consider using to make your code easier to create, scale and maintain in the future.
Summary of the Model View Controller MVC Design Pattern
Hopefully this covers the Model View Controller MVC design pattern in enough detail to understand why this is such a powerful design pattern to use when developing your web applications and also looks at the practicalities of implementing such a design pattern. Sure, you will certainly be writing more lines of code to implement such a design pattern although I can guarantee that you will be creating a much more efficient system overall and a system that is easier to scale and maintain in the future.
The key to implementing a great MVC design pattern throughout your web application comes down to planning. You need to be planning this design pattern extremely well and to make sure that your entire development team is working towards the same goals. It is important to discuss these things on a regular basis as this will ensure that everyone is developing code with this design pattern in mind.