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JavaServer Pages (JSP) is a Java technology that allows software developers to dynamically generate HTML, XML or other types of documents in response to a Web client request. The technology allows Java code and certain pre-defined actions to be embedded into static content. Image File history File links This is a lossless scalable vector image. ...
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HTML, an initialism of Hypertext Markup Language, is the predominant markup language for web pages. ...
The Extensible Markup Language (XML) is a general-purpose markup language. ...
A web browser is a software package that enables a user to display and interact with documents hosted by web servers. ...
The JSP syntax adds additional XML-like tags, called JSP actions, to be used to invoke built-in functionality. Additionally, the technology allows for the creation of JSP tag libraries that act as extensions to the standard HTML or XML tags. Tag libraries provide a platform independent way of extending the capabilities of a Web server. The Extensible Markup Language (XML) is a general-purpose markup language. ...
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The inside/front of a Dell PowerEdge web server The term Web server can mean one of two things: A computer program that is responsible for accepting HTTP requests from clients, which are known as Web browsers, and serving them HTTP responses along with optional data contents, which usually are...
JSPs are compiled into Java Servlets by a JSP compiler. A JSP compiler may generate a servlet in Java code that is then compiled by the Java compiler, or it may generate byte code for the servlet directly. JSPs can also be interpreted on-the-fly reducing the time taken to reload changes. The Java Servlet API allows a software developer to add dynamic content to a Web server using the Java platform. ...
A JSP compiler is a program that parses JavaServer Pages (JSPs), and transforms them into executable Java Servlets. ...
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JSP Weaver is a JavaServer Pages interpreter. ...
JSP and Servlets Architecturally, JSP can be viewed as a high-level abstraction of servlets that is implemented as an extension of the Servlet 2.1 API. Both servlets and JSPs were originally developed at Sun Microsystems, initially created by Manohar Rao Mankala and later elaborated on as a specification by Satish Dharmaraj. Starting with version 1.2 of the JSP specification, JavaServer Pages have been developed under the Java Community Process. JSR 53 defines both the JSP 1.2 and Servlet 2.3 specifications and JSR 152 defines the JSP 2.0 specification. As of May 2006 the JSP 2.1 specification has been released under JSR 245 as part of Java EE 5. The Java Servlet API allows a software developer to add dynamic content to a web server using the Java platform. ...
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The Java Community Process or JCP, established in 1995, is a formalized process which allows interested parties to be involved in the definition of future versions and features of the Java platform. ...
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Java 2 Platform, Enterprise Edition or Java EE (formerly also J2EE) is a programming platform — part of the Java platform — for developing and running distributed multi-tier architecture applications, based largely on modular components running on an application server. ...
JSP syntax A JavaServer Page may be broken down into the following pieces: - static data such as HTML
- JSP directives such as the include directive
- JSP scripting elements and variables
- JSP actions
- custom tags with correct library
JSP directives JSP directives control how the JSP compiler generates the servlet. The following directives are available: The Java Servlet API allows a software developer to add dynamic content to a web server using the Java platform. ...
- include
- The include directive informs the JSP compiler to include a complete file into the current file. It is as if the contents of the included file were pasted directly into the original file. This functionality is similar to the one provided by the C preprocessor. Included files generally have the extension "jspf" (for JSP Fragment):
<%@ include file="somefile.jspf" %> - page
- There are several options to the page directive.
- import
- Results in a Java
import statement being inserted into the resulting file. - contentType
- specifies the content that is generated. This should be used if HTML is not used or if the character set is not the default character set.
- errorPage
- Indicates the page that will be shown if an exception occurs while processing the HTTP request.
- isErrorPage
- If set to true, it indicates that this is the error page. Default value is false.
- isThreadSafe
- Indicates if the resulting servlet is thread safe.
- autoFlush
- To autoflush the contents.A value of true, the default, indicates that the buffer should be flushed when it is full. A value of false, rarely used, indicates that an exception should be thrown when the buffer overflows. A value of false is illegal when also using buffer="none".
- session
- To maintain session. A value of true (the default) indicates that the predefined variable session (of type HttpSession) should be bound to the existing session if one exists, otherwise a new session should be created and bound to it. A value of false indicates that no sessions will be used, and attempts to access the variable session will result in errors at the time the JSP page is translated into a servlet.
- buffer
- To set Buffer Size. The default is 8k and it is advisable that you increase it.
- isELIgnored
- Defines whether EL expressions are ignored when the JSP is translated.
- language
- Defines the scripting language used in scriptlets, expressions and declarations. Right now, the only possible value is "java".
- extends
- Defines the superclass of the class this JSP will become. You won't use this unless you REALLY know what you're doing - it overrides the class hierarchy provided by the Container.
- info
- Defines a String that gets put into the translated page, just so that you can get it using the genrated servlet's inherited getServletInfo() method.
- pageEncoding
- Defines the character encoding for the JSP. The default is "ISO-8859-1"(unless the contentType attribute already defines a character encoding, or the page uses XML document syntax).
<%@ page import="java.util.*" %> //example import <%@ page contentType="text/html" %> //example contentType <%@ page isErrorPage=false %> //example for non error page <%@ page isThreadSafe=true %> //example for a thread safe JSP <%@ page session=true %> //example for using session binding <%@ page autoFlush=true %> //example for setting autoFlush <%@ page buffer=20 %> //example for setting Buffer Size - Note: Only the "import" page directive can be used multiple times in the same JSP.
- taglib
- The taglib directive indicates that a JSP tag library is to be used. The directive requires that a prefix be specified (much like a namespace in C++) and the URI for the tag library description.
<%@ taglib prefix="myprefix" uri="taglib/mytag.tld" %> The C preprocessor (cpp) is the preprocessor for the C programming language. ...
A character encoding is a code that pairs a set of characters (such as an alphabet or syllabary) with a set of something else, such as numbers or electrical pulses. ...
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JSP scripting elements and objects
JSP implicit objects The following JSP implicit objects are exposed by the JSP container and can be referenced by the programmer: - out
- The JSPWriter used to write the data to the response stream.
- page
- The servlet itself.
- pageContext
- A
PageContext instance that contains data associated with the whole page. A given HTML page may be passed among multiple JSPs. - request
- The
HttpServletRequest object that provides HTTP request information. - response
- The HTTP response object that can be used to send data back to the client.
- session
- The HTTP session object that can be used to track information about a user from one request to another.
- config
- Provides servlet configuration data.
- application
- Data shared by all JSPs and servlets in the application.
- exception
- Exceptions not caught by application code .
HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...
Scripting elements There are three basic kinds of scripting elements that allow java code to be inserted directly into the servlet. - A declaration tag places a variable definition inside the body of the java servlet class. Static data members may be defined as well.
<%! int serverInstanceVariable = 1; %> Declaration tags also allow methods to be defined. <%! /** * Converts the Object into a string or if * the Object is null, it returns the empty string. */ public String toStringOrBlank( Object obj ){ if(obj != null){ return obj.toString(); } return ""; } %> - A scriptlet tag places the contained statements inside the
_jspService() method of the java servlet class. <% int localStackBasedVariable = 1; out.println(localStackBasedVariable); %> - An expression tag places an expression to be evaluated inside the java servlet class. Expressions should not be terminated with a semi-colon .
<%= "expanded inline data " + 1 %> - Also we can use the following tag to give comments in jsp:
<%-- give your comments here --%>
JSP actions JSP actions are XML tags that invoke built-in web server functionality. They are executed at runtime. Some are standard and some are custom (which are developed by Java developers). The following list contains the standard ones: - jsp:include
- Similar to a subroutine, the Java servlet temporarily hands the request and response off to the specified JavaServer Page. Control will then return to the current JSP, once the other JSP has finished. Using this, JSP code will be shared between multiple other JSPs, rather than duplicated.
- jsp:param
- Can be used inside a jsp:include, jsp:forward or jsp:params block. Specifies a parameter that will be added to the request's current parameters.
- jsp:forward
- Used to hand off the request and response to another JSP or servlet. Control will never return to the current JSP.
- jsp:plugin
- Older versions of Netscape Navigator and Internet Explorer used different tags to embed an applet. This action generates the browser specific tag needed to include an applet.
- jsp:fallback
- The content to show if the browser does not support applets.
- jsp:getProperty
- Gets a property from the specified JavaBean.
- jsp:setProperty
- Sets a property in the specified JavaBean.
- jsp:useBean
- Creates or re-uses a JavaBean available to the JSP page.
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A Java applet is an applet delivered in the form of Java bytecode. ...
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Examples of tags
jsp:include <html> <head></head> <body> <jsp:include page="mycommon.jsp" > <jsp:param name="extraparam" value="myvalue" /> </jsp:include> name:<%=request.getParameter("extraparam")%> </body> </html>
jsp:forward <jsp:forward page="subpage.jsp" > <jsp:param name="forwardedFrom" value="this.jsp" /> </jsp:forward> In this forwarding example, the request is forwarded to "subpage.jsp". The request handling does not return to this page.
jsp:plugin <jsp:plugin type=applet height="100%" width="100%" archive="myjarfile.jar,myotherjar.jar" codebase="/applets" code="com.foo.MyApplet" > <jsp:params> <jsp:param name="enableDebug" value="true" /> </jsp:params> <jsp:fallback> Your browser does not support applets. </jsp:fallback> </jsp:plugin> The plugin example illustrates a <html> uniform way of embedding applets in a web page. Before the advent of the <OBJECT> tag, there was no common way of embedding applets. Currently, the jsp:plugin tag does not allow for dynamically called applets. For example, jsp:params cannot be used with a charting applet that requires the data points to be passed in as parameters unless the number of data points is constant. You cannot, for example, loop through a ResultSet to create the jsp:param tags. Each jsp:param tag must be hand-coded. However, each of those jsp:param tags can have a dynamic name and a dynamic value. For other uses, see Plug in. ...
An applet is a software component that runs in the context of another program, for example a web browser. ...
jsp:useBean <jsp:useBean id="myBean" class="com.foo.MyBean" scope="request" /> <jsp:getProperty name="myBean" property="lastChanged" /> <jsp:setProperty name="myBean" property="lastChanged" value="<%= new Date()%>" /> The scope attribute can be request, page, session or application. It has the following meanings: - request
- the attribute is available for the lifetime of the request. Once the request has been processed by all of the JSPs, the attribute will be de-referenced.
- page
- the attribute is available for the current page only.
- session
- the attribute is available for the lifetime of the user's session.
- application
- the attribute is available to every instance and is never de-referenced. Same as a global variable.
The example above will use a Bean Manager to create an instance of the class com.foo.MyBean and store the instance in the attribute named "myBean". The attribute will be available for the life-time of the request. It can be shared among all of the JSPs that were included or forwarded-to from the main JSP that first received the request. In computer programming, a global variable is a variable that is accessible in every scope. ...
JSP Tag Libraries In addition to the pre-defined JSP actions, developers may add their own custom actions using the JSP Tag Extension API. Developers write a Java class that implements one of the Tag interfaces and provide a tag library XML description file that specifies the tags and the java classes that implement the tags.
Consider the following JSP.
<%@ taglib uri="mytaglib.tld" prefix="myprefix" %> ... <myprefix:myaction> <%-- the start tag %> ... </myprefix:myaction> <%-- the end tag %> ... The JSP compiler will load the mytaglib.tld XML file and see that the tag 'myaction' is implemented by the java class 'MyActionTag'. The first time the tag is used in the file, it will create an instance of 'MyActionTag'. Then (and each additional time that the tag is used), it will invoke the method doStartTag() when it encounters the starting tag. It looks at the result of the start tag, and determines how to process the body of the tag. The body is the text between the start tag and the end tag. The doStartTag() method may return one of the following: - SKIP_BODY
- The body between the tag is not processed.
- EVAL_BODY_INCLUDE
- Evaluate the body of the tag.
- EVAL_BODY_TAG
- Evaluate the body of the tag and push the result onto stream (stored in the body content property of the tag).
Note: If tag extends the BodyTagSupport class, the method doAfterBody() will be called when the body has been processed just prior to calling the doEndTag(). This method is used to implement looping constructs.
When it encounters the end tag, it invokes the doEndTag() method. The method may return one of two values:
- EVAL_PAGE
- This indicates that the rest of the JSP file should be processed.
- SKIP_PAGE
- This indicates that no further processing should be done. Control leaves the JSP page. This is what is used for the forwarding action.
The myaction tag above would have an implementation class that looked like something below: public class MyActionTag extends TagSupport { //Releases all instance variables. public void release() {...} public MyActionTag() { ... } //called for the start tag public int doStartTag() { ... } //called at the end tag public int doEndTag(){ ... } } Add Body Tag description.
If you want to iterate the body a few times, then the java class (tag handler) implements IterationTag interface. It returns EVAL_BODY_AGAIN - which means to invoke the body again.
JSP Standard Tag Library (JSTL) The JavaServer Pages Standard Tag Library (JSTL), is a component of the Java EE Web application development platform. It extends the JSP specification by adding a tag library of JSP tags for common tasks, such as XML data processing, conditional execution, loops and internationalization. The JavaServer Pages Standard Template Library, or JSTL, is a component of the J2EE web application development platform. ...
Internationalization Internationalization in JSP is accomplished the same way as in a normal Java application, that is by using resource bundles. Internationalization and localization are means of adapting products such as publications or software for non-native environments, especially other nations and cultures. ...
JSP 2.0 The new version of the JSP specification includes new features meant to improve programmer productivity. Namely: Hello, ${param.visitor} <%-- same as: Hello, <%=request.getParameter("param").getVisitor()%> --%> Expression Language (EL) is a scripting language to access Java components (JavaBeans). ...
This article is about Velocity as template engine. ...
In computer programming, templates are a feature of the C++ programming language that allow code to be written without consideration of the data type with which it will eventually be used. ...
Model-view-controller paradigm Sun recommends that the Model-view-controller pattern be used with the JSP files in order to split the presentation from request processing and computer data storage. Either regular servlets or separate JSP files are used to process the request. After the request processing has finished, control is passed to a JSP used only for creating the output. There are several platforms based on Model-view-controller pattern for web tiers (such as Barracuda, Apache Struts or Spring framework). This article or section should include material from Model view controller triad Model-View-Controller (MVC) is a software architecture that separates an applications data model, user interface, and control logic into three distinct components so that modifications to the view component can be made with minimal impact to...
For other uses, see Presentation (disambiguation). ...
1 GiB of SDRAM mounted in a personal computer. ...
Barracuda MVC is an open-source web application framework for developing Java EE web applications. ...
For the part of a car, see strut or suspension (vehicle). ...
The Spring Framework (or Spring for short) is an open source application framework for the Java platform. ...
Example Regardless of whether the JSP compiler generates Java source code for a servlet or emits the byte code directly, it is helpful to understand how the JSP compiler transforms the page into a Java servlet. For example, consider the following input JSP and its resulting generated Java Servlet.
Input JSP
<%@ page errorPage="myerror.jsp" %> <%@ page import="com.foo.bar" %> <html> <head> <%! int serverInstanceVariable = 1;%> ... <% int localStackBasedVariable = 1; %> <table> <tr><td><%= toStringOrBlank( "expanded inline data " + 1 ) %></td></tr> ... Resulting servlet package jsp_servlet; import java.util.*; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; import com.foo.bar; //imported as a result of <%@ page import="com.foo.bar" %> import ... class _myservlet implements javax.servlet.Servlet, javax.servlet.jsp.HttpJspPage { //inserted as a //result of <%! int serverInstanceVariable = 1;%> int serverInstanceVariable = 1; ... public void _jspService( javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response ) throws javax.servlet.ServletException, java.io.IOException { javax.servlet.ServletConfig config = ...;//get the servlet config Object page = this; PageContext pageContext = ...;//get the page context for this request javax.servlet.jsp.JspWriter out = pageContext.getOut(); HttpSession session = request.getSession( true ); try { out.print( "<html>rn" ); out.print( "<head>rn" ); ... //from <% int localStackBasedVariable = 1; %> int localStackBasedVariable = 1; ... out.print( "<table>rn" ); out.print( " <tr><td>" ); //from <%= toStringOrBlank( "expanded inline data " + 1 ) %> out.print( toStringOrBlank( "expanded inline data " + 1 ) ); out.print( " </td></tr>rn" ); ... } catch ( Exception _exception ) { //clean up and redirect to error page in <%@ page errorPage="myerror.jsp" %> } } }
See also The JavaServer Pages Standard Template Library, or JSTL, is a component of the J2EE web application development platform. ...
Java 2 Platform, Enterprise Edition or Java EE (formerly also J2EE) is a programming platform — part of the Java platform — for developing and running distributed multi-tier architecture applications, based largely on modular components running on an application server. ...
JavaServer Faces (JSF) is a Java-based Web application framework that simplifies the development of user interfaces for Java EE applications. ...
The Java Servlet API allows a software developer to add dynamic content to a Web server using the Java platform. ...
In computing, a WAR file (short for Web Application Archive) is a ZIP file used to distribute a set of Java classes. ...
An Enterprise ARchive, or EAR, is a file format used by Java EE for packaging one or more modules into a single archive so that the deployment of the various modules onto an application server happens simultaneously and coherently. ...
In computing, a JAR file (or Java ARchive) file used to distribute a set of Java classes. ...
Apache Tomcat is a web container, or application server developed at the Apache Software Foundation (ASF). ...
Sun Javaâ„¢ System Web Server (formerly Sun ONE Web Server, before that iPlanet Web Server, and before that Netscape Enterprise Server) is a web server designed for medium and large business applications. ...
Active Server Pages (ASP) is Microsofts server-side script engine for dynamically-generated web pages. ...
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Further reading Programming Perl is a classic OReilly book. ...
Programming Perl is a classic OReilly book. ...
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