Session 2: Using JSP Tags

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Session Objectives  Describe the various elements of a JavaServer Page  Describe the various JSP Tags in brief

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Session 2 Using JSP Tags
Session Objectives  Describe the various elements of a JavaServer Page  Describe the various JSP Tags in brief eACCP2003/Dynamic Pages Using JSP/ Session 2/ 2 of 45
What does a JSP look like?  Three main JSP constructs:  Directives  Allows one to control structure of the servlet  Scripting Elements  Used to include Java code  Actions  Specific tags that affect the runtime behavior of the JSPs eACCP2003/Dynamic Pages Using JSP/ Session 2/ 3 of 45
Fixed Template An Example data MyFirstProgram.jsp JSP Directive JSP Scriptlet JSP Expression eACCP2003/Dynamic Pages Using JSP/ Session 2/ 4 of 45
What happens under the hood? User Web Server/ Request Servlet Engine No JSP Handler Servlet New or (Page Compilation Servlet) modified file? Yes Compile into Execute Servlet Servlet eACCP2003/Dynamic Pages Using JSP/ Session 2/ 5 of 45
Various Elements in a JSP  Directives  page  Defines information that will be globally available for a JSP  include  Used to insert text and code at JSP translation time  taglib  Defines a mechanism for extending the current set of JSP tags eACCP2003/Dynamic Pages Using JSP/ Session 2/ 6 of 45
Different Attributes of the Page Directive Attribute Definition language = This attribute tells the server about the language to be ”” used to complete the JSP file. At present, Java is the only language that can be used. extends = This attribute defines the parent class that the generated ”" servlet will extend. import = This attribute defines the list of packages that will be ”" available to this JSP. However, a comma must separate each package. session = "true | false" This attribute determines whether the session data will be available to this page. The default is true. buffer = "none | " buffered. The default value is 8 kb. eACCP2003/Dynamic Pages Using JSP/ Session 2/ 7 of 45
Different Attributes of the Page Directive – (1) Attribute Definition autoFlush = "true | Determines whether the output buffer will be flushed false" automatically, or whether it will raise an exception when the buffer is full. The default is true. isThreadSafe = "true Specifies whether page can service more than one | false" request at a time. The default is true. info = ”" Specifies information about the JSP, can be accessed by Servlet.getServletInfo(). errorPage = This attribute represents the relative URL to the JSP ”" that will handle exceptions. isErrorPage = "true | This attribute states whether or not the JSP is an false" errorPage. The default is false. contentType = This attribute represents the MIME type and ”" character set of the response. eACCP2003/Dynamic Pages Using JSP/ Session 2/ 8 of 45
Using page Attributes An example JSP Elements JSP Elements eACCP2003/Dynamic Pages Using JSP/ Session 2/ 9 of 45
More on Directives  include directive  Syntax  taglib directive  Syntax eACCP2003/Dynamic Pages Using JSP/ Session 2/ 10 of 45
Some Important Points  While using directives, remember the following:  Directives are messages to the JSP container, that is, the JSP engine  Directives do not store any results in the output buffer  Directives are processed when the JSP is initialized eACCP2003/Dynamic Pages Using JSP/ Session 2/ 11 of 45
JSP Scripting Elements Scripting is a mechanism for embedding code fragments directly in an HTML page. The following three scripting elements are involved in JSP scripting:  Expressions  Scriptlets  Declarations eACCP2003/Dynamic Pages Using JSP/ Session 2/ 12 of 45
JSP Scripting Elements – (1) Expressions are evaluated to produce a java.lang.String type result. Syntax: Evaluated to Example: produce 4 2 + 2 equals eACCP2003/Dynamic Pages Using JSP/ Session 2/ 13 of 45
JSP Scripting Elements – (2) Scriptlets contain code that is valid for the language specified in the language directive. Java is the only language that is presently available. Syntax: Example: Scriptlet eACCP2003/Dynamic Pages Using JSP/ Session 2/ 14 of 45
JSP Scripting Elements – (3) Like expressions, scriptlets also have access to implicit variables. eACCP2003/Dynamic Pages Using JSP/ Session 2/ 15 of 45
JSP Scripting Elements – (4) Scriptlets do not need complete Java statements, and open blocks can affect the static HTML outside the scriptlets. 0.5) { %> Have a happy birthday!! Have a nice day!! eACCP2003/Dynamic Pages Using JSP/ Session 2/ 16 of 45
JSP Scripting Elements – (5) Declarations are the definition of classlevel variables and methods that are used in a JSP. Syntax: Example: Declaration This page has been accessed time(s) since the server was rebooted. eACCP2003/Dynamic Pages Using JSP/ Session 2/ 17 of 45
JSP Scripting Elements – (6) Points to remember about declarations:  Declarations do not produce any printable results.  Variables are initialized when the JSP is initialized.  Such variables are available to other declarations, expressions, and scriptlets.  Variables created through declarations become instance variables. Simultaneous users of the JSP share the same instance of the variable.  Class variables and functions can be declared in a declaration block. eACCP2003/Dynamic Pages Using JSP/ Session 2/ 18 of 45
JSP Standard Actions A JSP action directive provides an easy method to encapsulate common tasks. These typically create or act on objects, usually JavaBeans.        eACCP2003/Dynamic Pages Using JSP/ Session 2/ 19 of 45
JSP Standard Actions – (1)   Associates an instance of a predefined JavaBean with a given scope and ID   Sets the value of a bean’s property   Accesses the value of the specified property of a bean instance  Converts it to a java.lang.String object  Places it in the implicit out object eACCP2003/Dynamic Pages Using JSP/ Session 2/ 20 of 45