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JSP – Syntax ”; Previous Next In this chapter, we will discuss Syntax in JSP. We will understand the basic use of simple syntax (i.e, elements) involved with JSP development. Elements of JSP The elements of JSP have been described below − The Scriptlet A scriptlet can contain any number of JAVA language statements, variable or method declarations, or expressions that are valid in the page scripting language. Following is the syntax of Scriptlet − <% code fragment %> You can write the XML equivalent of the above syntax as follows − <jsp:scriptlet> code fragment </jsp:scriptlet> Any text, HTML tags, or JSP elements you write must be outside the scriptlet. Following is the simple and first example for JSP − <html> <head><title>Hello World</title></head> <body> Hello World!<br/> <% out.println(“Your IP address is ” + request.getRemoteAddr()); %> </body> </html> NOTE − Assuming that Apache Tomcat is installed in C:apache-tomcat-7.0.2 and your environment is setup as per environment setup tutorial. Let us keep the above code in JSP file hello.jsp and put this file in C:apache-tomcat7.0.2webappsROOT directory. Browse through the same using URL http://localhost:8080/hello.jsp. The above code will generate the following result − JSP Declarations A declaration declares one or more variables or methods that you can use in Java code later in the JSP file. You must declare the variable or method before you use it in the JSP file. Following is the syntax for JSP Declarations − <%! declaration; [ declaration; ]+ … %> You can write the XML equivalent of the above syntax as follows − <jsp:declaration> code fragment </jsp:declaration> Following is an example for JSP Declarations − <%! int i = 0; %> <%! int a, b, c; %> <%! Circle a = new Circle(2.0); %> JSP Expression A JSP expression element contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the JSP file. Because the value of an expression is converted to a String, you can use an expression within a line of text, whether or not it is tagged with HTML, in a JSP file. The expression element can contain any expression that is valid according to the Java Language Specification but you cannot use a semicolon to end an expression. Following is the syntax of JSP Expression − <%= expression %> You can write the XML equivalent of the above syntax as follows − <jsp:expression> expression </jsp:expression> Following example shows a JSP Expression − <html> <head><title>A Comment Test</title></head> <body> <p>Today”s date: <%= (new java.util.Date()).toLocaleString()%></p> </body> </html> The above code will generate the following result − Today”s date: 11-Sep-2010 21:24:25 JSP Comments JSP comment marks text or statements that the JSP container should ignore. A JSP comment is useful when you want to hide or “comment out”, a part of your JSP page. Following is the syntax of the JSP comments − <%– This is JSP comment –%> Following example shows the JSP Comments − <html> <head><title>A Comment Test</title></head> <body> <h2>A Test of Comments</h2> <%– This comment will not be visible in the page source –%> </body> </html> The above code will generate the following result − A Test of Comments There are a small number of special constructs you can use in various cases to insert comments or characters that would otherwise be treated specially. Here”s a summary − S.No. Syntax & Purpose 1 <%– comment –%> A JSP comment. Ignored by the JSP engine. 2 <!– comment –> An HTML comment. Ignored by the browser. 3 <% Represents static <% literal. 4 %> Represents static %> literal. 5 ” A single quote in an attribute that uses single quotes. 6 “ A double quote in an attribute that uses double quotes. JSP Directives A JSP directive affects the overall structure of the servlet class. It usually has the following form − <%@ directive attribute=”value” %> There are three types of directive tag − S.No. Directive & Description 1 <%@ page … %> Defines page-dependent attributes, such as scripting language, error page, and buffering requirements. 2 <%@ include … %> Includes a file during the translation phase. 3 <%@ taglib … %> Declares a tag library, containing custom actions, used in the page We would explain the JSP directive in a separate chapter JSP – Directives JSP Actions JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin. There is only one syntax for the Action element, as it conforms to the XML standard − <jsp:action_name attribute=”value” /> Action elements are basically predefined functions. Following table lists out the available JSP Actions − S.No. Syntax & Purpose 1 jsp:include Includes a file at the time the page is requested. 2 jsp:useBean Finds or instantiates a JavaBean. 3 jsp:setProperty Sets the property of a JavaBean. 4 jsp:getProperty Inserts the property of a JavaBean into the output. 5 jsp:forward Forwards the requester to a new page. 6 jsp:plugin Generates browser-specific code that makes an OBJECT or EMBED tag for the Java plugin. 7 jsp:element Defines XML elements dynamically. 8 jsp:attribute Defines dynamically-defined XML element”s attribute. 9 jsp:body Defines dynamically-defined XML element”s body. 10 jsp:text Used to write template text in JSP pages and documents. We would explain JSP actions in a separate chapter JSP – Actions JSP Implicit Objects JSP supports nine automatically defined variables, which are also called implicit objects. These variables are − S.No. Object & Description 1 request This is the HttpServletRequest object associated with the request. 2 response This is the HttpServletResponse object associated with the response to the client. 3 out This is the PrintWriter object used to send output to the client. 4 session This is the HttpSession object associated with the request. 5 application This is the ServletContext object associated with the application context. 6 config This is the ServletConfig object associated with the page. 7 pageContext This encapsulates use