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What is the difference between JSF, Servlet and JSP?

I have some questions. These are :

How are JSP and Servlet related to each other?
Is JSP some kind of Servlet?
How are JSP and JSF related to each other?
Is JSF some kind of Pre-Build UI based JSP like ASP.NET-MVC?

Answer*

### [JSP (JavaServer Pages)][1]

JSP is a **Java view technology** running on the server machine which allows you to write template text in client side languages (like HTML, CSS, JavaScript, ect.). JSP supports [taglibs][2], which are backed by pieces of Java code that let you control the page flow or output dynamically. A well-known taglib is [JSTL][3]. JSP also supports [Expression Language][4], which can be used to access backend data (via attributes available in the page, request, session and application scopes), mostly in combination with taglibs.

When a JSP is requested for the first time or when the web app starts up, the servlet container will compile it into a class extending [`HttpServlet`][5] and use it during the web app's lifetime. You can find the generated source code in the server's work directory. In for example [Tomcat][6], it's the `/work` directory. On a JSP request, the servlet container will execute the compiled JSP class and send the generated output (usually just HTML/CSS/JS) through the web server over a network to the client side, which in turn displays it in the web browser.

### [Servlets][7]

Servlet is a **Java application programming interface (API)** running on the server machine, which intercepts requests made by the client and generates/sends a response. A well-known example is the `HttpServlet` which provides methods to hook on [HTTP][8] requests using the popular [HTTP methods][9] such as `GET` and `POST`. You can configure `HttpServlet`s to listen to a certain HTTP URL pattern, which is configurable in `web.xml`, or more recently with [Java EE 6][10], with `@WebServlet` annotation.

When a Servlet is first requested or during web app startup, the servlet container will create an instance of it and keep it in memory during the web app's lifetime. The same instance will be reused for every incoming request whose URL matches the servlet's URL pattern. You can access the request data by [`HttpServletRequest`][11] and handle the response by [`HttpServletResponse`][12]. Both objects are available as method arguments inside any of the overridden methods of `HttpServlet`, such as `doGet()` and `doPost()`.

### [JSF (JavaServer Faces)][13]

JSF is a **component based MVC framework** which is built on top of the Servlet API and provides [components][14] via taglibs which can be used in JSP or any other Java based view technology such as [Facelets][15]. Facelets is much more suited to JSF than JSP. It namely provides great [templating capabilities][16] such as [composite components][17], while JSP basically only offers the [`<jsp:include>`][18] for templating in JSF, so that you're forced to create custom components with raw Java code (which is a bit opaque and a lot of tedious work) when you want to replace a repeated group of components with a single component.  Since JSF 2.0, JSP has been deprecated as view technology in favor of Facelets.

**Note**: JSP itself is NOT deprecated, just the combination of JSF with JSP is deprecated.

**Note**: JSP has great templating abilities by means of Taglibs, especially the ([Tag File][2]) variant.  JSP templating in combination with JSF is what is lacking.

As being a MVC ([Model-View-Controller][19]) framework, JSF provides the [`FacesServlet`][20] as the sole request-response *Controller*. It takes all the standard and tedious HTTP request/response work from your hands, such as gathering user input, validating/converting them, putting them in model objects, invoking actions and rendering the response. This way you end up with basically a JSP or Facelets (XHTML) page for *View* and a JavaBean class as *Model*. The JSF components are used to bind the view with the model (such as your ASP.NET web control does) and the `FacesServlet` uses the *JSF component tree* to do all the work.

### Related questions

- [What is the main-stream Java alternative to ASP.NET / PHP?][21]
- [Java EE web development, what skills do I need?][22]
- [How do servlets work? Instantiation, session variables and multithreading][23]
- [What is a Javabean and where are they used?][24]
- [How to avoid Java code in JSP files?][25]
- https://stackoverflow.com/questions/5104094/what-components-are-mvc-in-jsf-mvc-framework
- https://stackoverflow.com/questions/4421839/what-is-the-need-of-jsf-when-ui-can-be-achieved-from-css-html-javascript-jquery/

[1]: https://stackoverflow.com/tags/jsp/info
  [2]: http://docs.oracle.com/javaee/5/tutorial/doc/bnann.html
  [3]: https://stackoverflow.com/tags/jstl/info
  [4]: https://stackoverflow.com/tags/el/info
  [5]: http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServlet.html
  [6]: http://tomcat.apache.org
  [7]: https://stackoverflow.com/tags/servlets/info
  [8]: http://www.w3.org/Protocols/rfc2616/rfc2616.html
  [9]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
  [10]: http://docs.oracle.com/javaee/6/tutorial/doc/bnafd.html
  [11]: http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletRequest.html
  [12]: http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletResponse.html
  [13]: https://stackoverflow.com/tags/jsf/info
  [14]: http://docs.oracle.com/javaee/6/tutorial/doc/bnarf.html
  [15]: http://docs.oracle.com/javaee/6/tutorial/doc/giepx.html
  [16]: http://docs.oracle.com/javaee/6/tutorial/doc/giqxp.html
  [17]: http://docs.oracle.com/javaee/6/tutorial/doc/giqzr.html
  [18]: http://java.sun.com/products/jsp/syntax/2.0/syntaxref2020.html#8828
  [19]: http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller
  [20]: http://docs.oracle.com/javaee/6/api/javax/faces/webapp/FacesServlet.html
  [21]: https://stackoverflow.com/questions/2556553/what-is-the-main-stream-java-alternative-to-asp-net-php
  [22]: https://stackoverflow.com/questions/1958808/java-web-development-what-skills-do-i-need
  [23]: https://stackoverflow.com/questions/3106452/java-servlet-instantiation-and-session-variables
  [24]: https://stackoverflow.com/questions/1727603/places-where-java-beans-used
  [25]: https://stackoverflow.com/questions/3177733/howto-avoid-java-code-in-jsp-files

Edit Summary*

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@BalusC : I have seen this type of code used in jsp instead of java code - <c:forEach items="${items}"> <jsp:attribute name="var"> <mytag:doesSomething/> </jsp:attribute> What is this?

Ashwin
– Ashwin

2012-04-23 06:40:52 +00:00
Commented Apr 23, 2012 at 6:40
8

@Shashank: Not entirely. Only the <c:forEach> tag is from JSTL. See also stackoverflow.com/tags/jstl/info

BalusC
– BalusC

2012-09-29 11:22:48 +00:00
Commented Sep 29, 2012 at 11:22
1

Yes. <mytag:doesSomething/> looks like a custom tag and <jsp:attribute>, a jsp tag.

Shashank Kadne
– Shashank Kadne

2012-09-29 11:43:19 +00:00
Commented Sep 29, 2012 at 11:43
4

Since this is a hugely popular answer, I want to add a very important bit which is JSP tag files which allows for custom tag creation for page composition and layout without writing Java code. This feature is extremly useful and has been part of the standard for many years yet remains underutilized.

jiggy
– jiggy

2014-09-01 20:41:42 +00:00
Commented Sep 1, 2014 at 20:41
1

@johnny Facelets has been the preferred view technology since Java EE 6 was released in 2009 (docs.oracle.com/javaee/6/tutorial/doc/giepx.html). The minimum set of technologies to develop Java web apps isn't higher than most other languages, but there are many more options and competitors, which is confusing to newcomers. Web development in Ruby? The first choice is obvious.

user201891
– user201891

2014-09-10 00:11:43 +00:00
Commented Sep 10, 2014 at 0:11

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What is the difference between JSF, Servlet and JSP?

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