Struts, Spring and a few other frameworks implement the MVC architecture to separate the representation of information from the user's interaction with it.
Can any one explain or give me a link for that in Java EE?
Without using a framework, how can I create an MVC application and what are the design patterns needed for that?
Take a look at this presentation, which is part of Beginning & Intermediate Servlet & JSP Tutorials on http://www.coreservlets.com/
you can use Servlet and Jsp to create a MVC application without using any framework,
here are some useful links,
http://forum.codecall.net/topic/72183-mvc-application-in-java/
another useful example,
http://css.dzone.com/articles/web-mvc-java
I think this is a good tutorial on Creating MVC architecture with servlets and jsp
The main concern in creating MVC architecture is the separation of concerns. You need to separate business layer, presentation layer and controler layer
Model layer is achieved by simple POJO
View layer i.e. Presentation layer can be achieved by JSP
Controllers can be achieved by servlets in java ee
MVC stands for Model View and Controller. It is a design pattern that separates the business logic, presentation logic and data.
Controller acts as an interface between View and Model. Controller intercepts all the requests.
Model represents the state of the application i.e. data.
View represents the presentaion.
This link contains an example to implement it with JSP and Servelet.
You can use Servlets and JSP directly.
For managing Java EE applications we are using design patterns.
MVC-1 and MVC-2 are design patterns for managing the UI layer.
Struts and Spring-MVC are implementations of the MVC-2 design pattern.
To answer you first question: the part of the Java EE framework that implements MVC is called JSF. This provides templates, graphical components (widgets) and much more.
To answer your second question: you don't really build an MVC app without any framework. You may be using Servlets and JSP, but that too is a framework. Java EE in its entirety is a (full stack) framework as well.
As for the third question: this is simple, the design pattern to use for MVC is MVC.
Related
I've read the code from this Spring MVC application:
https://github.com/spring-guides/tut-rest/tree/master/6/complete/src/main/java/com/yummynoodlebar/core/events
I don't understand the role of those classes from events folder. How can
I catch such a event in another place in application?
Another thing which I don't understand at this application, is why
they doesn't use command-query separation somewhere at service layer. They
used CQS on their rest controllers. I'm not agree with that, instead, they
should use CQS on service-layer to provide a easy way to add validation
or other core operations to their services. This link describes what I'm
talking about CQS separation on service layer.
If you have suggestions about how to implement the CQS pattern described in
the link from above, please tell it.
I need to get a few things cleared up. I have been looking for an answer for this one, but I can't seem to find a good answer to my specific questions (eg. this question was nibbling on the answer: Difference between servlet and web service).
To my understanding, there are different ways you can implement the "request handling", aka "Controller", in an "MVC oriented" web application, two of them being:
A Java specific Servlet (ie. one you create by clicking new ->
Servlet, in eclipse for example), used as a "Controller". This one
extends HttpServlet and you use methods like doGet and doPost etc.
A Spring MVC annotated #Controller class (yes, using a DispatcherServlet). With this one you use the #RequestMethod GET/POST etc.
Now to my questions...
When do you use one or the other?
Are there any general advantages to use one method over the other? (Like, is one method recommended over the other in general?)
[EDIT]: Emphasized keywords
If you're a student interested in learning the language then I would stick with servlets for now. It's possible to write a web app using just servlets but in practice you'll probably want to look at JSP's too.
A JSP is a convenient way to write a servlet that allows you to mix html with scripting elements (although it's recommended to avoid Java code in your jsp in favour of tags and el expressions). Under the covers it will be compiled as a servlet but it avoids you having to use lots of messy print statements.
It's important to have at least a basic understanding of servlets and JSP's. Spring MVC is one of many frameworks built on top of servlets to try make the task of writing a web application a bit easier. Basically all requests are mapped to the DispatcherServlet which acts as a front controller.
The DispatcherServlet will then call the controller whose annotations match the incoming request. This is neater than having to write these mappings yourself in the web.xml (although with servlet 3.0 you can annotate servlets now). But you also get many other benefits that can be used like mapping form fields to an object, validating that object with jsr303 annotations, map inputs and outputs to xml or json etc etc. Plus it's tightly integrated with core spring so you can easily wire in your services for the controller to call.
It's worth noting that there are a plethora of competing frameworks built on top of servlets. Spring MVC is one of the most popular so it's not a bad choice to look into.
A Servlet and a Spring MVC Controller can be used to do the same thing but they act on different level of a Java Application
The servlet is a part of the J2EE framework and every Java application server (Tomcat, Jetty, etc) is built for running servlets. Servlet are the "low level" layer in the J2EE stack. You don't need a servlet.jar to run you application because it's prepackaged with the application server
A Spring MVC controller is a library built upon the servlet to make things easier. Spring MVC offers more built-in functionalities such as form parameter to controller method parameter mapping, easier handling of binary form submissions (i.e. when your form can upload files). You need to package the required jars to your application in order to run a Spring MVC Controller
You should use a servlet when you need to go "low level", and example could be for performance reason. Spring MVC performs good but if it has some overhead, if you need to squeeze out all you can from your application server (and you have already tuned the other layers such as the db) go with a servlet. You can choose a servlet if you want to understand the foundation of the J2EE web specifications (i.e. for educational purposes)
In all the other cases you can/should choose a web framework. Spring MVC is one of them; with Spring MVC you don't need to reinvent the wheel (i.e binary form management, form parameter to bean conversion, parameter validation and so on).
Another plus of Spring MVC is that in one class you can easily manage input from different urls and methods, doing the same in a servlet is possible but the code is more complicated and less readable.
My opinion is that Spring MVC is good for building rest services and managing simple applications (i.e web application with simple forms). If you need to manager very complex forms with Ajax, nested forms, and an application with both session and page state my advice is to switch to a component based framework (like apache wicket for example).
JSF and JSP aswell as Spring MVC builts upon Servlets. The problem this that servlets are not very "nice" to work with because you have to write direct html.
If you are able to use mordern web technologies I would just use servlets in positions that need direct http output like writing an image from a database to http.
Using SpringMVC or JSF which work with a Dipatcherservlet or FacesServlet is just faster and more fun. They parse your files and send it through a servlet.
So, yeah, this is what I understood.
Servlet is just an intermediary responsible for finding out what the parameters in the request mean. These parameters are given to the .java file. It is a mere intermediary
.java file is the Model which does business logic
View is the JSP that will do the presentation
Did I get that right?
The Model View Controller pattern is not specific to Java or Servlet technology. There are many non-java MVC implementations, and in Java, there are non-Servlet implementations (Swing is an example).
In Java, when using Servlet-based MVC, usually an MVC framework is used. There are two main categories here: action based and component based, the difference being that action based frameworks listen each registered URL independently while component based frameworks keep a component tree and maintain server-side state.
Action based frameworks are Spring MVC, Struts 1+2, Stripes, Play etc. Component based frameworks are Wicket, JSF 1 & 2, Tapestry etc.
Your diagram gets close to the truth, but there are a few subtle misconceptions.
First, it doesn't make sense to speak of .java files. Java source files are totally irrelevant to a deployed web application, it uses compiled .class files only, and the JavaVM can be programmed in many different languages, so the application doesn't care whether the .class files were compiled from Java, Scala, Groovy, JRuby, Clojure, AspectJ or anything else as long as they comply to the Java Class File specification.
Second, while JSP has long been the default view technology in Java Servlet technology, it's far from the only one. Other technologies include Facelets, Velocity, Freemarker etc., and there's also nothing to stop you from writing data directly to a request from a controller without a dedicated view technology (although this is usually not advisable).
Basically, what MVC stands for is a system where there is separate code for business logic (the M), the view technology (V) and the Controller that ties things together. In a well-organized MVC architecture, the M part is so well encapsulated that the same business logic can also be executed through other channels (e.g. web services, direct library access etc.). Also, it should be possible to switch view technologies through configuration from the outside without editing the actual controller logic.
I would advise you to read the docs for the Spring MVC framework, it is to my knowledge the most robust (and also easy-to-use) MVC framework out there, and the tooling support is also great (in either InteliJ Idea or the Eclipse-based SpringSource Tool Suite).
When you are talking about MVC, then all three layers should be separated from each other.
In web application :
1: A controller should be responsible handling the user request then filtering & executing the appropriate actions and then forward the generated response to the client.
2: A model consist of your Business logic,beans & Pojo classes. This should deal with you logic ,perform some operation and renders the generated result to some kind of persistent object or DTO's.
3: A view is consist of your GUI, some presentation-logic , it should be separated from your back-end ,ultimately you are showing an encapsulated form of result to your client i.e. what a client actually needed.
There are two types of MVC: MVC1(Push-MVC) and MVC2(Pull-MVC)
Pull-MVC and Push-MVC are better understood with how the view layer is getting data i.e. Model to render. In case of Push-MVC the data( Model) is constructed and given to the view layer by the Controllers by putting it in the scoped variables like request or session. Typical example is Spring MVC and Struts1. Pull-MVC on the other hand puts the model data typically constructed in Controllers are kept in a common place i.e. in actions, which then gets rendered by view layer. Struts2 is a Pull-MVC based architecture, in which all data is stored in Value Stack and retrieved by view layer for rendering.
I like the concept of MVC, and Spring provides one, called Spring MVC. However it looks like it targets on web application.
If I want to use MVC concept in Spring environment, how to do that?
MVC has nothing to do with Spring; it is a software design architecture/design pattern that you can apply to separate out disparate parts of a software codebase (Model, View and Controller). So long as you implement all your business logic in your model, your GUI logic in your view and your controller responds to any events occuring on your view and updating the view as necessary based on the model then you're adhering to the MVC pattern.
This article shows how MVC would be implemented in a Swing environment. Spring MVC can only ever be used as a web framework. The Spring Framework itself however can still be used wherever you want as it is not tied to a Servlet-based architecture (IoC container).
Once you get to grips with MVC another design pattern/architecture, which is closely related to MVC called MVP (Model View Presenter) is interesting, although very similar, seems to me to be a valid successor to MVC as it completely dumbs down the GUI side.
It is a bit more high level, but you may want to look at Spring RCP project.
I am using MVC design pattern in jsp-servlet web application, and want to what is the exact difference between MVC1 and MVC2 , can someone help?
EDIT newly I hear that there is 2 versions of using MVC in servlet programming, I hear that in MVC1 there is kind of coupling between controller and view , but in MVC2 they overtake it, if someone know whether this is right or wrong I'll be very thankful.
It might be possible that you read this version in connection with asp.net MVC, as there different versions of that framework. There is no version 2.0 of the mvc pattern, just a version 2.0 of the asp.net MVC framework.
In context of jsp servlets see: Model 1 and Model 2. In a nutshell: Model 1 doesn't have a controller to dispatch requests, Model 2 does.
In MVC 1, controller and model,both are JSP. While in MVC2 controller is servlet and model is java class.
In MVC1 there is tight coupling between page and model as data access is usually done using Custom tag or through java bean call.
In MVC2 architecture there is only one controller which receives all the request for the application and is responsible for taking appropriate action in response to each request.
MVC1 was a first generation approach that used JSP pages and the JavaBeans component architecture to implement the MVC architecture for the Web. HTTP requests are sent to a JSP page that implements Controller logic and calls out to the Model for data to update the View. This approach combines Controller and View functionality within a JSP page and therefore breaks the MVC paradigm. MVC1 is appropriate for simple development and prototyping. It is not, however, recommended for serious development.
MVC2 is a term invented by Sun to describe an MVC architecture for Web-based applications in which HTTP requests are passed from the client to a Controller servlet which updates the Model and then invokes the appropriate View renderer-for example, JSP technology, which in turn renders the View from the updated Model.
The hallmark of the MVC2 approach is the separation of Controller code from
content. (Implementations of presentation frameworks such as Struts, adhere to the MVC2 approach).
That's what I found here: http://www.theserverside.com/discussions/thread.tss?thread_id=20685
MVC-1 Architecture
1) In MVC-1 Architecture, single web component(Servlet/JSP) is used as Controller and view but for other layers separate web components are taken....
2) Since, single component is taken as Controller and view, logics are mixed up..
MVC-2 Architecture
1) In MVC-2 Architecture separate components should be taken for separate layers...
2) Logics are not mixed, there is clean separation between the logics....