What is the difference between JSF, Servlet and JSP?

Question

I have some questions. These are :

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

Solution 1

JSP (JavaServer Pages)

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, which are backed by pieces of Java code that let you control the page flow or output dynamically. A well-known taglib is JSTL. JSP also supports Expression Language, 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 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, 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

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 requests using the popular HTTP methods such as GET and POST. You can configure HttpServlets to listen to a certain HTTP URL pattern, which is configurable in web.xml, or more recently with Java EE 6, 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 and handle the response by HttpServletResponse. Both objects are available as method arguments inside any of the overridden methods of HttpServlet, such as doGet() and doPost().

JSF (JavaServer Faces)

JSF is a component based MVC framework which is built on top of the Servlet API and provides components via taglibs which can be used in JSP or any other Java based view technology such as Facelets. Facelets is much more suited to JSF than JSP. It namely provides great templating capabilities such as composite components, while JSP basically only offers the <jsp:include> 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) variant. JSP templating in combination with JSF is what is lacking.

As being a MVC (Model-View-Controller) framework, JSF provides the FacesServlet 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.

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Solution 2

See http://www.oracle.com/technetwork/java/faq-137059.html

JSP technology is part of the Java technology family. JSP pages are compiled into servlets and may call JavaBeans components (beans) or Enterprise JavaBeans components (enterprise beans) to perform processing on the server. As such, JSP technology is a key component in a highly scalable architecture for web-based applications.

See https://jcp.org/en/introduction/faq

A: JavaServer Faces technology is a framework for building user interfaces for web applications. JavaServer Faces technology includes:

A set of APIs for: representing UI components and managing their state, handling events and input validation, defining page navigation, and supporting internationalization and accessibility.

A JavaServer Pages (JSP) custom tag library for expressing a JavaServer Faces interface within a JSP page.

JSP is a specialized kind of servlet.

JSF is a set of tags you can use with JSP.

Solution 3

From Browser/Client perspective

JSP and JSF both looks same, As Per Application Requirements goes, JSP is more suited for request - response based applications.

JSF is targetted for richer event based Web applications. I see event as much more granular than request/response.

From Server Perspective

JSP page is converted to servlet, and it has only minimal behaviour.

JSF page is converted to components tree(by specialized FacesServlet) and it follows component lifecycle defined by spec.

Solution 4

Servlets :

The Java Servlet API enables Java developers to write server-side code for delivering dynamic Web content. Like other proprietary Web server APIs, the Java Servlet API offered improved performance over CGI; however, it has some key additional advantages. Because servlets were coded in Java, they provides an object-oriented (OO) design approach and, more important, are able to run on any platform. Thus, the same code was portable to any host that supported Java. Servlets greatly contributed to the popularity of Java, as it became a widely used technology for server-side Web application development.

JSP :

JSP is built on top of servlets and provides a simpler, page-based solution to generating large amounts of dynamic HTML content for Web user interfaces. JavaServer Pages enables Web developers and designers to simply edit HTML pages with special tags for the dynamic, Java portions. JavaServer Pages works by having a special servlet known as a JSP container, which is installed on a Web server and handles all JSP page view requests. The JSP container translates a requested JSP into servlet code that is then compiled and immediately executed. Subsequent requests to the same page simply invoke the runtime servlet for the page. If a change is made to the JSP on the server, a request to view it triggers another translation, compilation, and restart of the runtime servlet.

JSF :

JavaServer Faces is a standard Java framework for building user interfaces for Web applications. Most important, it simplifies the development of the user interface, which is often one of the more difficult and tedious parts of Web application development.
Although it is possible to build user interfaces by using foundational Java Web technologies(such as Java servlets and JavaServer Pages) without a comprehensive framework designedfor enterprise Web application development, these core technologies can often lead to avariety of development and maintenance problems. More important, by the time the developers achieve a production-quality solution, the same set of problems solved by JSF will have been solved in a nonstandard manner. JavaServer Faces is designed to simplify the development of user interfaces for Java Web applications in the following ways:
• It provides a component-centric, client-independent development approach to building Web user interfaces, thus improving developer productivity and ease of use.
• It simplifies the access and management of application data from the Web user interface.
• It automatically manages the user interface state between multiple requests and multiple clients in a simple and unobtrusive manner.
• It supplies a development framework that is friendly to a diverse developer audience with different skill sets.
• It describes a standard set of architectural patterns for a web application.

[ Source : Complete reference:JSF ]

Solution 5

There are also situations where you can favor JSP over JSF. The application nature should be the deciding factor to choose the technology.

If you have a rich GUI interaction and lot of Java scripting needed then favor JSF. Basically if your GUI app architecture is like Component oriented & even driven like Swing then JSF is the best.

If the application is just a plain form submitting, not much of GUI interaction needed, then JSP could do well if learning a new tech is an overhead and also complex framework is unnecessary.

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