Creating JavaServer Pages

milklivereddeepInternet και Εφαρμογές Web

13 Νοε 2013 (πριν από 5 χρόνια)

101 εμφανίσεις

1
- Rambabu Manchikalapudi
Creating JavaServer Pages
TM
- Server-Side Scripting language (Basically HTML with Java
Code or JSP tags usage and a file with “.jsp” extension).
- Cross Platform/ Cross WebServer method of creating
Dynamic and Interactive webpages.
- Part of the Java
TM
2 Enterprise Edition by Sun Microsystems
and shares the “ Write Once, Run Anywhere
TM”
characteristics
and the Power of JAVA programming language.
What is JSP
TM
?
2
- To provide an efficient answer to CGI Scripting technology
which lacks scalability.
- To Adapt to the requirement for dynamic web pages and
separate business logic from Programming logic.
- Harness the power of a scripting language that is built on a
complete Programming Language (Java).
- Ability to access enterprise services ( DB, CORBA, RMI).
Why JavaServer Pages
TM
?
JSP and JavaBeans
- JavaBeans are reusable software components written in Java.
- Similar to ActiveX components,but designed to be platform-
neutral and running anywhere there is a Java Virtual Machine.
- To use a JavaBean with a JSP, use the tags <useBean/>,
<setProperty/>, and <getProperty/>. (Do getProperty & setProperty 1
st
)
- JavaBeans are used in JSP files to add functionality, enable
debugging and provide modularity to the JSP page.
3
JSP and Servlets
- Servlets are similar to applets, but run on the server.
- They facilitate independent, interactive web applications.
- JSP pages eventually get compiled into servlets when sent onto
the server side.
- Servlets are a secure method of transaction processing as they h
have information about the clients and use SSL (Secure socket
layer to transmit data).
- Both JSP and Java servlets share all the features of the Java 2
Enterprise Edition.
- JSP and Java servlets rely on re-usable, cross platform
components known as JavaBeans and Enterprise Java Beans.
Components :
- Webserver is a software that accepts requests from the
and sends information back to be displayed on the browser.
Ex: Apache Web Server available at http://www.apache.org
- Container is a software that stores JSP files,Servlets,transforms
JSP files to servlets, compiles and runs servlets producing HTML.
Ex: Tomcat Container also developed by Apache Software, available
at http://jakarta.apache.org
Browser
JSP File
Complilation
Servlet
Servlet Container
Request
Response
JSP
TM
Architecture
4
JSP
TM
tags and Syntax
• Directives
- Page Directive tag.
- Include Directive tag.
• Declarations tag.
• Expressions and Scriptlets tag.
• Comments tag.
Directive tags
- Are Messages to the JSP engine.
- Do not produce any visible output.
- JSP directives are always enclosed within the
<%@ ... %> tags.
- The two primary directives are ‘page’ and ‘include’.
- JSP version 1.1 provides support for one other
type of directive called the “taglib” directive used for
custom tag libraries.
5
Page and Include Directives
• A Page directive is typically found at the top of the JSP Page.
There can be any number but attribute/value pair must be
unique.
Ex: <%@ page import=“java.util.*,com.abc.*” buffer=“16k” %>
This makes available the types declared within the packages
mentioned and sets the page bufferingto 16k.
• An Include directive seperates the page contents into more
manageable elements by including a HTML or a JSP file content into
the current file.
Ex: <%& include file=“showcart.jsp” %>
Declaration tag
• Page level variables to save information and define methods that
the rest of the JSP page will need.
• Declarations are always found within the <%!….. %> tags.
• Always end variable declarations with a semicolon.
Ex: <%! Int I=0; %>
• Methods also can be declared to override an existing method
Ex : <%! Public void JspInit(){
// some code
}
%>
• If there is a lot of logic-intensive components, JavaBeans can be
used to help in better debugging and improve re-usability.
6
Expressions and Scriptlets tag
Expressions
- Evaluation result of strings directly embedded into HTML page
- They have the <%= ….%> tags and do not have semicolons
Ex : <%= somevar %> , <%= somebean.getName() %>
Scriptlets
- Any Java code within a scriptlet & can run into multiple lines.
- Scriplets have <%…%> tags and are of the following form
Ex: <% for(int I=0; I<=4; I++) {
<b>Hello</b>
}
%>
Page Forward tag
- When multiple JSP pages are required to process a request,
a page forward tag is used to send all information to another page
- An include request also often serves the same purpose.
- Two ways to forward, request “parameters” and “attributes”.
- String values only can be passed using the request parameters
shown here
Ex : <jsp:forward page="login.jsp">
<jsp:param name="errMsg“
value="The name or password is not valid" />
</jsp:forward>
- If an object needs to be passed, a JavaBean is used with the request
attributes method. The bean is created by the first page and forwarded to
the second.
7
Comment/hidden comment tag
- This is similar to comments in the regular HTML page
except that users cannot view the comments when they
“view source” the page.
- The comments are embedded in <%-- ….. --%> tag.
Ex : <%-- This comment is for me --%>
- Can be used effectively during the debugging and testing
process by blocking scriptlets before page compilation.
JSP
TM
Object Scopes & Implicit Objects
Application
Most
Visible
Least
Visible
Session
Request
Page
- Objects are created implicitly using JSP directives, explicitly
through actions and directly through Scripting code.
- 4 types of visibility scopes.
- Nine Implicit Objects in JSP
• HttpServletRequest triggers service invocation :
Request Scope.
• HttpServletResponse responds to the request :
Page Scope
• PageContext gives implementation dependant
features : Page Scope
• ServletContext obtains servlet configuration :
Application Scope
• JspWriter object writes to the Output stream : Page Scope
• ServletConfig has the configuration of the JSP page : Page Scope
• HttpJspPage refers to the same page and is like a “this” pointer : Page Scope
• HttpSession refers to a particular session that the JSP page is in : Session Scope
• Throwable refers to an uncatched exception that resulted in error page : Page Scope
8
Exception Handling
- JSP provides a good mechanism for handling runtime exceptions.
- It is possible to provide customized error handling.
- By use of the page directive’s “errorPage” object an uncaught
exception can be forwarded to an appropriate JSP page for
processing. The sending page should then, for example, be marked
as
<%@ page isErrorPage=“false” errorPage=“error.jsp” %>
- The “error.jsp” page in question has to mark itself as an error
handling page by using a similar statement.
<%@ page isErrorPage=“true” %>
so that, the throwable object of the exception can be accessed
through the implicit exception object of the new page.
Request Chaining
- Used primarily to process HTML forms.
- It is a method of passing beans around different JSP pages in an
application which are embedded in a request object by the
initiating page.
- The bean is extracted by the servlet or JSP page to which it is
passed, alters attributes if necessary, adds new attributes or adds
another JavaBean in the request process and sends it to another
page.
-The <jsp:include> tag can be used to redirect the request to any
static or dynamic resource which is in the same context as the
calling page.
9
Synchronization
-The servicing mechanism of a JSP page is multithreaded.
- It has to be ensured that access to the shared state is synchronized.
- It can be done by simply including the following in the JSP page
<% page isThreadSafe=“True” %>
-This will ensure that multiple copies of servlet are loaded in the
memory and client requests are served from these copies in the
servlet pool in a round robin fashion.
- However, this solution is not scalable and causes delay in the client
service method and therefore is ineffective.
- Other better approach is to do it by explicitly synchronizing acess to
shared objects using scriptlets.
Session Management
- All JSP pages take part in HttpSession and all linked JSP pages can access information
stored in other JSP files using the “session” implicit object unless excluded by having the
statement
<%@ page session=“false” %>.
- Primitive data types are not allowed. Only Java Objects.
- Beans and Objects that need to be shared across other pages are stored in
sessions.
- Session objects are identified by session ID stored in browser as cookie.
- A session object maybe created and shared across the session as follows :
<% car a= new car();
session.putValue=(“xyz”, a);
%>
- It maybe retrieved in another page by using a statement, for example :
<% car newcar=(car).session.getValue(“xyz”);
%> ( Type casting must be done carefully)
- No.of Objects (HeapSpace Consideration) and limit max.objects possible.
10
JSP
TM
Vs ASP
TM
Similarities
- Create Interactive web pages.
- Faster and easier than CGI.
- Use Object Oriented Scripting.
- Use Component Technology.
- ASP+ (Part of .NET from Microsoft) feels more like JSP
in that the pages compile dynamically and are executed on
a virtual machine written in C#.
JSP
TM
Vs ASP
TM
cont’d…
Differences
- Platforms :ASP runs only on Microsoft
®
Windows whereas JSP
runs also on Solaris, Mac OS and Linux.
- Webservers :ASP runs on Microsoft
®
IIS or personal
webserver and select servers using third-party software
whereas JSP runs on most of the existing servers.
- Component Model :ASP uses Win-32 COM model whereas JSP
uses JavaBeans and Enterprise JavaBeans.
- Scripting :ASP supports VBScript and Jscript while JSP uses pure Java
or JavaScript.
- Security Model :ASP uses Win NT and JSP uses Java Security model.
- DataBase Access :ASP uses “Active Data Objects” while JSP uses JDBC
for database access.
- Custom tags :Custom tag library is supported in JSP and not in ASP.
11
Advantages of JSP
TM
- Open, Extensible & Portable standard for building dynamic webpage.
- JSP is more powerful than JavaScript and Server Side Includes.
-- Servlets are closely similar but JSP helps in sharing the design
load and also by implementing JavaBeans it is modular.
- It wins over ASP in terms of Platform independancy, Web Server
compatibility and being portable.
- Dynamic content can be catered to HTML/DHTML,Wireless
phones and PDA’s.
- Customizable tag library to cater to a variety of applications.
- Power of JAVA and robust since it is interpreted, not interpreted.
JSP 1.2 Specifications Final Release
http://jcp.org/aboutJava/communityprocess/first/jsr053/index.html
Future of JSP
TM
- Entirely dependant on the fate of Java Programming Language.
- Here to stay, since the standard is open to change and JSP is Cross
platform.
- Compatibility and Co-existance with other emerging standards like
XML ensures growth and continued usage.
12
References
- SUN Microsystems Product website for JSP
http://java.sun.com/products/jsp/index.html
- APACHE HTTP Web Server for JSP support
http://httpd.apache.org/
- Jakarta Tomcat Project (Web Container for JSP)
http://jakarta.apache.org/tomcat/index.html