CODEWITHSUNDEEP
htmljspjakarta-eemodel-view-controllerservlets
Lali Pali
Lali Pali

Reputation: 627

Why present view with servlet if we can do it with jsp?

It seems that both can represent a view, that is if you request a servlet it will show you an html page, and so the same if you request a jsp file, just the way they are implemented are different.

Now I know that servlet are more than, that. They control requests and so on, but still after reading so many days, still don't know how to use them in harmony together.

If i need some logic, do I put it in a servlet, and then what? How do I present my data, from the servlet or from a jsp file located in the same folder?

In other words, do I even need jsp files when I use servlet, and if yeas why???

Upvotes: 0

Views: 480

Answers (2)

Ravi K Thapliyal
Ravi K Thapliyal

Reputation: 51721

It seems that both can represent a view, ...

JSP was introduced because it's much easier to invoke Java to render parts that are dynamic in an otherwise static HTML template rather than trying to print out the whole page in Java through servlets (too many println(), escaping quotes etc. it's a mess). So, JSP is better suited for rendering views.

MVC is all about separation of concerns: request handling and routing, business logic and application data, and the views with all the presentation logic.

JSPs later enhanced with EL (Expression Language), JSTL (Java Standard Tag Lbrary) and other such tag libraries that encapsulate the presentation logic are better suited to support the View layer.

Model represents your application data and all the business rules that you apply on them. They're implemented as POJOs (plain old Java objects i.e. not extending or implementing platform specific classes or interfaces) .

Servlets and Filters with their request dispatching capabilities and inherently existing in the Java environment are better suited as Controllers to interact with the Application Server, the Model and the View. They facilitate all the routing and the flow of data between the three layers.

If i need some logic, do I put it in a servlet, and then what?

Your business logic neither goes in Servlets nor JSPs. That goes into your business classes (POJOs) insulated as much as possible from the type of application platform (which is J2EE here).

A simple request to demonstrate its use would be to ask you to port your application into .Net. A-ha! Suddenly, writing all that business logic inside your Servlets/JSPs, that cannot be easily reused now, doesn't feel like such a good idea.

So, ideally, your servlets would intercept the client requests and invoke some business class to fulfill it. This may return some data (like results from a SQL query) wrapped as a domain data object (also referred to as data value or data transfer objects).

How do I present my data, from the servlet or from a jsp file located in the same folder?

Before redirecting to an appropriate View, the Controller servlet would push the domain object into some scope (could be request, session or application depending on the requirements) or a sophisticated data store available with an MVC framework (like the ValueStack in Struts 2).

The View, which is your JSP, would then pull the domain object from one of these scopes or ValueStack and render its required properties for display through EL with JSTL tags or OGNL expressions with tag libraries provided by the MVC framework.

Upvotes: 2

lamed
lamed

Reputation: 21

It is of good style to separate logic from presentation. (1) You can easily change the logic not touching the presentation and vice versa. (2) You can use a right tool for each task. Pure Java in servlet's code is good for implementing logic. Templating engine, including JSP, is good for presentation, where your work is largely in HTML with some points where you're inserting data from the application.

You can read about Spring as an example how to use JSP in the best way.

Upvotes: 1

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