Java Servlets + state = How to?

Question

In my web application i want to have certain necessary things in all of the "pages" of it, such as connection to the database, user information, template processing, etc. Until recently i would have an abstract servlet that would init all of the above in its doGet or doPost method, define the abstract method doLocalLogic(HttpServletRequest req, HttpServletResponse res) and would call it from the doGet/doPost method. All the extending classes would enjoy the database connection, user info, etc. Unfortunately, it turned out to be bad practice.

What I am thinking now is to create an abstract class that does all that, all the logic from my servlets would be moved to the children of this class, and the servlets would just create instances of those children.

However, that leads to creating one more class per every page in my app. Moreover, when you create a new servlet, you don't have any clues in the form of abstract methods you need to override, as you would having an abstract servlet.

Is there a better way of doing it?

@TomaszNurkiewicz Well, what got me thinking is getting two or more full pages in the same browser window. I.e. i would get two or more copies of the same page when i pressed and held F5. In some cases, i would get +1 error message when i repeated an action that caused the error (that is the error message would be just added to the error stack, which I thought would be reinited). I started reading up on the subject and i read that keeping state in servlets was a bad idea. — Ibolit
– Ibolit, Commented Nov 17, 2012 at 19:45

Tomasz Nurkiewicz · Accepted Answer · 2012-11-17 19:12:44Z

2

First of all I would argue that your approach with doLocalLogic() is not bad as long as you are passing this local logic through parameters, not through fields (threads are shared between requests/threads):

public void doLocalLogic(
  Connection connection,
  UserInformation user,
  //...
  HttpServletRequest req,
  HttpServletResponse res
)

The only problem is that you do prepare a lot of data even if you don't need them in the servlet. And it's not scalable.

What you really need is a more robust... framework. First you probably need a web framework to avoid coding to servlet API directly. Secondly you need IoC like Spring to manage your dependencies. Instead of eagerly creating them and passing over, each service just asks for required dependencies.

edited Nov 17, 2012 at 19:12

answered Nov 17, 2012 at 19:04

Tomasz Nurkiewicz

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1 Comment

Ibolit Over a year ago

To me, Spring looks like a bit of overkill. On the one hand, my application is not that big (at least, yet), on the other, I thought that "HttpServlet" was basically that kind of framework :) Basically, most of the objects I need in to pass to my objects are singletons, so the idea with passing them as parameters looks really good. But i will have another look at Spring, though.

Yair Zaslavsky · Accepted Answer · 2012-11-17 19:11:53Z

1

I would recommend using a framework like spring-mvc
The framework will let you implement MVC in your web application.
It will let you pass an application context throughout the request flow,
and even to pass it among different pages handlign , from what I remember;
and will of course let you separate most of the logic from the Servlet classes.

answered Nov 17, 2012 at 19:11

Yair Zaslavsky

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4 Comments

Ibolit Over a year ago

I do implement MVC in my app even without Spring-MVC. In my design, Servlets are the Controllers, database is the Model and View are the FreeMarker templates. To me, Spring looks just a bit too heavyweight.

Yair Zaslavsky Over a year ago

Spring is very modular, comparing with Java EE (or at least what it used to be prior to Java EE 6). In my humble opinion, implementing your "in house" code when there is a framework that is so widely used should be really justified besides a "gut feeling" of "heavyweight".

Ibolit Over a year ago

This is a good point. However, using a framework should also be justified. That is a subject for a separate holy war :) Sometimes, using a framework is like using concrete blocks to build a garden shed. But again, i will look into Spring.

Yair Zaslavsky Over a year ago

I agree - I suggest that you look at Spring-MVC and see if it helps you. I can tell you that in general, I found myself writing spring-mvc like code , without being aware to spring-mvc, and it was stupid. even if i used only 50% of the features , and not all of spring-mvc in my code - writing my own code for this was stupid.

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