JSF、Servlet 和 JSP 之间有什么区别？

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?

Answer 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 HttpServlet s 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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Answer 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.

Answer 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.

Answer 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 ]

Answer 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.

Answer 6

Servlet - it's java server side layer.

• JSP - it's Servlet with html
• JSF - it's components base on tag libs
• JSP - it's converted into servlet once when server got request.

Answer 7

的确，JSP在执行的时候就被转换成servlet，而JSF是一个全新的东西，目的是让网页更具可读性，因为JSF允许以标签的形式编写所有的编程结构。

Answer 8

The basic difference between Servlets and JSP is that in Servlets we write java code and in that we embed HTML code and there is just reverse case with JSP . In JSP we write HTML code and in that we embed java code using tags provided by JSP.

Answer 9

Java Server Pages (JSP) is java technology which enables Web developers and designers to rapidly develop and easily maintain, information-rich, dynamic Web pages that leverage existing business systems. JSP technology separates the user interface from content generation, enabling designers to change the overall page layout without altering the underlying dynamic content.

Facelets is the first non JSP page declaration language designed for JSF (Java Server Faces) which provided a simpler and more powerful programming model to JSF developers as compare to JSP. It resolves different issues occurs in JSP for web applications development.

Here is a table that compares the features of scriplets and facelets:

Source

Answer 10

JSP:means HTML+Java Code:

JSP have it's own life cycle jsp_init() jsp_service() jsp_destroy

After first request JSP convert to .java file. There is three type of tag we are using
1.)Scriptless

<%  %>

Here developer can declare all those things which developer want to take the data

2.)Expression tag

<%=  %>

Here developer can use some print related data

3.)Declaration

<!% %>

Here developer can declare some method related data.

Servlet:

Servlet have it's own life cycle.

init()
service()
destroy()

After first request container will read the data from web.xml file then after out welcome fill will be display.
Now onward after performing action it will search the url and after this process it will search the particular servlet there it self. service operation will perform.

JSF:

JSF have it's own ui and it's life cycle can perform in six way,

A)Restore view phase
B)Apply request values phase
C)Process validations phase
D)Update model values phase
E)Invoke application phase
F)Render response phase

For ui here for table here we are using panel grid and there is different faces for this that is.

Rich Faces
Prime Faces.

Answer 11

JSPs are the View component of MVC (Model View Controller). The Controller takes the incoming request and passes it to the Model, which might be a bean that does some database access. The JSP then formats the output using HTML, CSS and JavaScript, and the output then gets sent back to the requester.

Answer 12

JSF is an advanced framework wherein its very easy to implement Model-View-Controller (MVC) based architecture for projects. Main advantage of JSF over JSP is the easy dynamic rendering of the components on the browser based upon conditions and easy integration of ajax events.

The front end of the JSF application ie xhtml files are the ones which are shown to the user via browser. These xhtml files internally invoke managed beans eg controllers wherein actual application logic is written.

The controllers internally invoke various services which communicate with database (using Hibernate or JPA API). This is how the flow happens in short.

JSF is also used in combination with RichFaces which is a framework for giving rich look and feel to your web application.

JSF + RichFaces + Hibernate/JPA is a good technology to learn for sure !

Answer 13

Jsp is also having in built servlet code which don't need any external compilation it can be run directly run. Changes will take effect in jsp directly in a browser.

Servlet need to be compiled (ie it will have specific class creation)

Jsf is a view component of MVC Framework

Answer 14

JSP stands for JAVA SERVER PAGE........ jsp is not a servlet. Jsp uses code and HTML tag both in itself you dont need to make a HTML and a servlet seprately.Jsp are playing magnificent role in web application. Servlet is a java class plays an role to make your HTML page from static to dynamic .

Answer 15

Servlets are the server side java programs which execute inside the web container. The main goal of the servlet is to process the requests received from the client.

Java Server Pages is used to create dynamic web pages. Jsp's were introduced to write java plus html code in a single file which was not easy to do in servlets program. And a jsp file is converted to a java servlet when it is translated.

Java Server Faces is a MVC web framework which simplifies the development of UI.